U.S: Army Coast: Ens. Res-Ctr. MR 77-7 ( MI) (AD-Aose 7103) Laboratory Effects in Beach Studies. Volume MII. Analysis of Results from 10 Movable-Bed Experiments. by Charles B. Chesnutt MISCELLANEOUS REPORT NO. 77-7 (VII) JUNE 1978 W HOTS Approved for public release; distribution unlimited. U.S. ARMY, CORPS OF ENGINEERS COASTAL ENGINEERING ay RESEARCH CENTER ayes Bs Kingman Building S Fort Belvoir, Va. 22060 Osg| Mie AEL Reprint or republication of any of this material shall give appropriate credit to the U.S. Army Coastal Engineering Research Center. Limited free distribution within the United States of single copies of this publication has been made by this Center. Additional copies are available from: National Technical Information Service ATTN: Operations Division 5285 Port Royal Road Springfield, Virginie 22151 The findings in this report are not to be construed as an official Department of the Army position unless so designated by other authorized documents. UNCLASSIFIED SECURITY CLASSIFICATION OF THIS PAGE (When Data Entered) READ INSTRUCTIONS REPORT DOCUMENTATION PAGE 1. REPORT NUMBER 2. GOVT ACCESSION NO 3. RECIPIENT'S CATALOG NUMBER 4. TITLE (and Subtitle) 5. TYPE OF REPORT & PERIOD COVERED LABORATORY EFFECTS IN BEACH STUDIESs Miscellaneous Report Volume VIII. Analysis of Results from 10 Movable-Bed Experiments 6. PERFORMING ORG. REPORT NUMBER 8. CONTRACT OR GRANT NUMBER(a) 7. AUTHOR(s) Charles B. Chesnutt 10. PROGRAM ELEMENT, PROJECT, TASK AREA & WORK UNIT NUMBERS D31192 12. REPORT DATE June 1978 13. NUMBER OF PAGES VA OS Si ye 15. SECURITY CLASS. (of this report) o PERFORMING ORGANIZATION NAME AND ADDRESS Department of the Army Coastal Engineering Research Center (CERRE-CP) Kingman Building, Fort Belvoir, Virginia 22060 11. CONTROLLING OFFICE NAME AND ADDRESS Department of the Army Coastal Engineering Research Center Kingman Building, Fort Belvoir, Virginia 22060 14. MONITORING AGENCY NAME & ADDRESS(if different from Controlling Office) UNCLASSIFIED 15a. DECLASSIFICATION/ DOWNGRADING SCHEDULE 16. DISTRIBUTION STATEMENT (of this Report) Approved for public release; distribution unlimited. 17. DISTRIBUTION STATEMENT (of the abstract entered in Block 20, if different from Report) 18. SUPPLEMENTARY NOTES 19. KEY WORDS (Continue on reverse side if necessary and identify by block number) Breakers Model studies Wave height variability Beach profiles Movable-bed experiments Wave reflection Coastal engineering Wave envelopes Wave tanks Currents Wave generators 20. ABSTRACT (Continue om reverse side if neceasary and identify by block number) Variation in wave reflection from a movable bed as it adjusted to the impinging waves was the primary source of wave height variability in 10 experiments in 6- and 10-foot-wide wave tanks. Re-reflection of waves from the wave generator, secondary waves, transverse waves, and cross waves also contributed to the wave height variability. (continued) FORM DD . jan 7a 1473 = EDITION OF ? NOV 6511S OBSOLETE SECURITY CLASSIFICATION OF THIS PAGE (When Data Entered) UNCLASSIFIED SECURITY CLASSIFICATION OF THIS PAGE(When Data Entered) The reflection coefficient, Kp, variation ranged from 0.02 to 0.12 in one experiment to as much as from 0.04 to 0.27 in another experiment. Changes in the foreshore slope and berm-crest elevation, the breaker type, the slope and top elevation of the offshore slope, and the distance between the fore- shore and offshore were the sources of the Kp variability. For a constant initial profile slope, the average K increased with increasing wavelength; but for a constant wavelength, the average Kp, decreased with increasing initial profile slope. In nine experiments the Kp tended to increase as the profile developed, indicating that the profile was reflecting, rather than absorbing, energy. Profile equilibrium was not easily attained, particularly in five experi- ments with a wave steepness of 0.021, which. is in the transition region betwee "winter" and "summer'' waves. Experiments with winter or summer waves reached equilibrium more readily. Laboratory effects, caused by differences in initial profile slope, initia test length (distance between the wave generator and the initial shoreline), tank width, and water temperature, affected the profile development and the wave height variability. Initial profile slope and initial test length should be kept constant to assure test repeatability in movable-bed experiments. The wavelength-to-tank width ratio should be greater than or equal to 3 to assure two dimensionality of profile development, but two-dimensional profiles may not be realistic replications of three-dimensional profiles. 2 UNCLASSIFIED SECURITY CLASSIFICATION OF THIS PAGE(When Data Entered) PREFACE Ten experiments were conducted at the Coastal Engineering Research Center (CERC) from 1970 to 1972 as part of an investigation of the Laboratory Effects in Beach Studies (LEBS), to relate wave height variability to wave reflection from a movable- bed profile in a wave tank. The investigation also identified the effects of other laboratory constraints. The LEBS project is directed toward the solution of problems facing the laboratory researcher or engineer in charge of a model study; ultimately, the results will be of use to field engineers in the analysis of model studies. The work was carried out under the CERC coastal processes research program. This report (Vol. VIII) is the last in a series of eight volumes on the LEBS ex- periments. Volume I describes the procedures used in the 10 LEBS experiments, and serves as a guide for conducting coastal engineering laboratory studies; Volumes II to VII are data reports covering all experiments. This volume is a comprehensive analysis of results from all 10 experiments, and includes a further analysis of each experiment and how it relates to the other 9 ex- periments on wave height variability, profile equilibrium, and laboratory effects. This report was prepared by Charles B. Chesnutt, principal investigator, under the general supervision of Dr. C.J. Galvin, Jr., Chief, Coastal Processes Branch. The author gratefully acknowledges the assistance of the following CERC employees who were involved in the LEBS data collection or reduction: J.C. Ahlquist, R.J. Brown, W.J. Brown, S.M. Bruce, J.W. Buchanan, E.G. Burroghs, D.A. Clark, D.M. Clark, G. Davis, W.O. Doll, J.M. D'Ottavio, J.M. Fairchild, E. Fishman, A.B. Frankle, D.C. French, M. Fuhr, H. Goldstein, B.H. Gwinnup, W.J. Herr, F. Holcombe, R.R. Kohler, F. Lago, M.W. Leffler, F.S. Moore, J.J. Moore, D.A. Mowrey, M.J. Murphy, P.C. Pritchett, B.D. Schiappa, K.E. Schreiter, Jr., R.M._Small, L.C. Tate, C.F. Thomas, W.A. Thompson, T.M. Thrall, and C.V. Willard. Computer programs used in the data reduction were written by J.C. Ahlquist, S.M. Bruce, J.W. Buchanan, and B.A. Sims; programs written by J.C. Ahlquist used techniques developed by W.R. James and 0.S. Madsen. Significant contri- butions were made by C.H. Everts, R.J. Hallermeier, C. Mason, and E.F. Thompson through numerous discussions with the author and by reviewing one or more of the early manu- scripts. The author extends special appreciation to the following: M.W. Leffler for his assistance in the preparation of the eight manuscripts; C.J. Galvin, Jr., for his guidance and assistance; and R.P. Stafford, for the high quality of the data collected and who coauthored the first seven volumes. Comments -on this publication are invited. Approved for publication in accordance with Public Law 166, 79th Congress, approved 31 July 1945, as supplemented by Public Law 172, 88th Congress, approved 7 November 1963. JOHN H. COUSINS Colonel, Corps of Engineers Commander and Director CONTENTS Page CONVERSION FACTORS, U.S. CUSTOMARY TO METRIC (SI) ....... 9 Th: DNBRODUWGTLON aiydih SERRANO ed OR | RO OR RA tai PLS ee in a eave a Mn Sion aeme a Le LSS Baek er Oui Arie » Wes RAE 8 ey Pare tema eae taste) wileya Oeraieteee otra tee Tie pe toutes meme 7h ee ay Bil oxoU aI NS] OKOMGLASE. is NNEC cls Mio oe ‘Go oko Toe Mol ohiGi,Jo.- 6) kom lah otros! vo UT Se SCOP Cs eu china astece el aouesclpieiys shinee) ngohece Phccliee ares SMM clamy Sure CR pe Wyow) (oaks uae Oe LL, sWAVE sHELGHTSVARTABIOLIIYG tran a. as sree Sit Wb lod aa Seid otmerome-m veunrem 9105) li Detainittion) ot Merms <5. Ap a eo POSED OT RESON. 5 GS Aare ETE 2. Variations in Wave Reilocihion. PSG ck ooh comets a tea een oactomgerc ion elh7/ So Webmlarcioms sin imengcemic Were OREN so 6 66 60 6 6 0 6 a 4 1 EQUTEEBREUMPPRO EIGE Saas) scutes ere SO) 1. Definitions and inypomeemes of Boma lates: Broelles oo 6 0 OY Be jesesyers: Ose) Ibpalicaleul escosentiley, Salojseno “ao og o d- 0 6 0 6 oo. 0 Sil Je bitect.of WaverPerlod® ver: ii soli Pot eRe Sei eee Si [Vj LABORATORY sERPE GIS 6 iy vig viele caqie)taliamoree ek Rene ae = temitog te) garcia mee eee S/S) 1. Definitions of Terms . . SARA Me bars n oesulr 210 ie MITA 2. Test Length and Initial Slope feeecces! Si EMRE HRS bv: aA M/S 53 ante: Wares bie CES coer yais cc 2) brs crseay Beye ss, Bs MoI gs, PReHACIRY Ed ELEC el ES, AV WekeGre Temperature BIBFECES 6 6560 5 6 5 0 Bo oo oo OZ So Onciaesp Welbyonrenconay WimreeeS 6° 6566 6 6 0 690 6 6b oO 6 oo co LID V CONCLUSIONS .. . BUNS RE, Ses RD DE What 2a Goewl KO 1. Wave Height Wai cihacsy . MERU RON nO MbeRC Ec MD Mo CeMde sas oaks. oso LID 2 PrOt le xe Guile UMen ve vos, , fargass ae ie) eh gore ony ot pete enna Ope Magee: 3. sLaboratory, BERCCES we c.ckisciis ) Worm erechsciy om coh Gil sWh cnctbieme-yer tr mire LOS VI RECOMMENDATIONS FOR CONDUCTING MOVABLE-BED COASTAL EXPERIMENTS. 123 1. Modeling Criterion... SHUTS, ARTIS BD LOE SL 2S 2. Tank Setup and Test Gondteions She eer ual als indi eka Siadit Sem towne “ca cel La) Loads R EUS) on YS eaWeeneIbON Ns ome. Woe Ma GuieneaRaGysdeno Go. or ou oro oo! 6 LDA EETERATUREWGDRDEDS (2) 39.0. Ee meee ht emrcy oes kom WaCoN CRE pa WR ene maton e TABLES i Semmes Oi SxqoSrelinemcal GomGkelOMS oo 5 605650050660. &2 2 Average reflection coefficient and limits of values in each DBAS SGI 5 5 0 0 6 oo KOK OHO Ooo CY 3 Summary of profile development in experiment 72C-10. ...... 21 4 Summary of profile development in experiment 70X-06. ..... . 23 5 Summary of profile development in experiment 70X-10. ..... . 26 6 Summary of profile development in experiment 71Y-06. ...... 28 7 Summary of profile 8 Summary of profile 9 Summary of profile 10 Summary of profile 11 Summary of profile 12 Summary of profile 13 Incident wave heigh CONTENTS TABLES--Continued development in experiment 71Y-10. development in experiment 72D-06. development in experiment 72B-06. development in experiment 72B-10. development in experiment 72A-06. development in experiment 72A-10. ts. 14 Known laboratory effects FIGURES 1 Definition sketch of profile zones (experiment 71Y-06) 2 Reflection variabil in experiment 72C- 3 Reflection variabil in experiment 70X- 4 Reflection variabil in experiment 70X- 5 Reflection variabil in experiment 71Y- 6 Reflection variabil in experiment 71Y- 7 Reflection variabil in experiment 72D- 8 Reflection variabil ity and 10. ity and 06. ity and OF: ity and 06. ity and 10. ity and 06. ity and with a 2.35-second wave . 9 Reflection variabil 10 Correlation between experiment. 11 Correlation between ity and Kp and offshore slope steepness in each Kp and shelf length in each experiment . movement of the -0.8-foot contour movement movement movement movement movement of the -0.7-foot of the -0.7-foot of the -0.7-foot of the -0.7-foot of the -0.7-foot contour contour contour contour contour contour movement in experiments movement of critical contours in experiments with a 3.75-second wave . 12 Contour movements along center range of experiment 71Y-06. Page 31 34 37 38 41 43 47 120 14 20 22 25 27 30 32 35 39 13 14 15 16 107, 18 19 20 21 22 23 24 25 26 Bi 28 29 30 31 32 CONTENTS FIGURES--Continued Contour movements along center range of experiment 72D-06. Comparison of final profiles with a 1.90-second wave and different initial slopes. Contour movements along center range of experiment 72C-10. Equilibrium profile in experiment 72C-10, with steep "winter'' wave . Contour movements along center range of experiment 70X-06. Contour movements along center range of experiment 70X-10. Greater seaward development of profile in experiment 70X-10 than in experiment 70X-06 Profile changes in experiment 70X-10 during the last 35 hours. Contour movements along center range of experiment 71Y-10. Greater seaward development of the profile in experiment 71Y-06 than in 71Y-10 . Final profiles in experiments 71Y-06 and 71Y-10, with the longest test durations in the series. Aims) Mamites, Comparison of final profiles with a wave period of 1.90 seconds and an initial slope of 0.10. Contour movements along center range of experiment 72B-06. Contour movement along center range of experiment 72B-10 . Development of different offshore shapes: concave upward in experiment 72B-06 and convex upward in experiment 72B-10. Contour movements along center range of experiment 72A-06. Contour movements along center range of experiment 72A-10. Development of a higher foreshore in experiment 72A-10 and a steeper offshore in experiment 72A-06 . Profile change in experiment 72A-06 during the last 55 hours . Comparison of the equilibrium or representative profile for each wave steepness . Page 5S 54 56 57 58 59 60 61 62 63 65 65 66 67 68 69 70 71 72 74 33 34 35 36 SU 38 39 40 41 42 43 44 45 46 47 48 CONTENTS FIGURES--Continued Preliminary beach profile of Vitale (personal communication, 1976), developed from the final profiles of experiments 72C-10, 71Y-10, 72B-10, and 72A-10. Sich Be RCS, tact Comparison of shoreline movement in four experiments with a 1.90-second wave and a 0.10 initial slope . Shoreline movement of five ranges in experiment 72C-10 (L/W = 1.03). Foreshore variability over 35-hour period in experiment 72C-10 (L/W = 1.03) Lateral variations in movement of inshore zone contours in experiment 72C-10 (L/W = 1.03). Lack of lateral variations in movement of offshore zone contours in experiment 72C-10 (L/W = 1.03). Profile shape at end (140 hours) of experiment 72C-10 (L/W = 1.03). ; 56 tet Spano Ree “ota Shoreline movement in experiments 70X-10 and 71Y-10 (L/W = 1.43). Comparison of the movements of the -0.6-foot contour in experiments 70X-10 and 71Y-10 (L/W = 1.43). Profile shape at end of experiments 70X-10 and 71Y-10 (L/W = 1.43). : eased nei. Shoreline movement in experiments 70X-06, 71Y-06, and 72D-06 (L/W = 2.38). Comparison of the -0.6-foot contour movements in experiments 70X-06, 71Y-06, and 72D-06 (L/W = 2.38) Profile shape at end of experiments 70X-06, 71Y-06, and 72D-06 (L/W = 2.38) A CASES A Atl meh ae ar SORE Mae a Shoreline movement in experiment 72B-10 (L/W = 1.86) Lateral variations in the movements of inshore zone contours in experiment 72B-10 (L/W = 1.86) Lateral variations in the movements of offshore zone contours in experiment 72B-10 (L/W = 1.86) Page 74 Tei 81 82 83 84 85 87 88 89 90 91 93 94 95 96 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 CONTENTS FIGURES--Continued Profile shape at end (150 oe of auras 72B-10 (L/W = 1.86). Beate : : sigs isTye Shoreline movement in experiment 72B-06 (L/W = 3.10) Comparison of the movements of inshore zone contours in experiment 72B-06 (L/W = 3.10). Comparison of the movements of offshore zone contours in experiment 72B-06 (L/W = 3.10). Profile shape at end (150 ee of experiment 72B-06 (L/W = 3.10). 5 0 0 Rie AP EE A Meee crate Shoreline movement in experiment 72A-10 (L/W = 3.14) Comparison of the movements of offshore zone contours in experiment 72A-10 (L/W = 3.14). Profile shape at end (80 pane of coed Onna 72A-10 (L/W = 3.14). auliin : : advtel 6. Gunes Shoreline movement in experiment 72A-06 (L/W = 5.23) Comparison of the movements of upper offshore zone contours in experiment 72A-06 (L/W = 5.23) Comparison of the movements of lower offshore zone contours in experiment 72A-06 (L/W = 5.23) Profile shape at end Ose cae of ee” 72A-06 (E/We= 85925) eos cieacatae ative saan. Comparison of daily mean water temperatures and shoreline positions in experiment 72C-10. Comparison of daily mean water temperatures and shoreline positions in experiments 70X-06 and 70X-10. Comparison of daily mean water temperatures and shoreline positions in experiments 71Y-06 and 71Y-10. Comparison of daily mean water temperatures and shoreline positions in experiment 72D-06. Comparison of daily mean water temperatures and shoreline positions in experiments 72B-06 and 72B-10. Comparison of daily mean water temperatures and shoreline positions in experiments 72A-06 and 72A-10. Page 7 98 100 101 102 103 104 105 106 108 109 110 112 114 116 117 118 CONVERSION FACTORS, U.S. CUSTOMARY TO METRIC (SI) UNITS OF MEASUREMENT U.S. customary units of measurement used in this report can be converted to metric (SI) units as follows: eee __eeeeeeee_____s_______ Ee Multiply inches Square inches cubic inches feet square feet cubic feet yards square yards cubic yards miles square miles knots acres foot-pounds millibars ounces pounds ton, long ton, short degrees (angle) by To obtain ee eee ______|_ le 25.4 millimeters 2.54 centimeters 6.452 Square centimeters 16.39 cubic centimeters 30.48 centimeters 0.3048 meters 0.0929 square meters 0.0283 cubic meters 0.9144 meters 0.836 square meters 0.7646 cubic meters 1.6093 kilometers 259.0 hectares 1.852 kilometers per hour 0.4047 hectares 1.3558 newton meters 1.0197 x 1073 kilograms per square centimeter 28.35 grams 453.6 grams 0.4536 kilograms 1.0160 metric tons 0.9072 metric tons 0.01745 radians 5/9 Celsius degrees or Kelvins! Fahrenheit degrees eee 1To obtain Celsius (C) temperature readings from Fahrenheit (F) readings, use formula: Co= (5/9) (Es =32)). To obtain Kelvin (K) readings, use formula: K = (5/9) (F -32) + 273.15. i oie i scigroesen % a mre ie des fi ge a ah: tae 10 i LABORATORY EFFECTS IN BEACH STUDIES Volume VIII. Analysis of Results from 10 Movable-Bed Experiments by Charles B. Chesnutt I. INTRODUCTION Laboratory effects, caused by differences in tank width, initial slope, distance between the generator and the profile, gaps at the end of the generator blade, and, perhaps, even water temperature, can hinder the solution of coastal engineering problems in movable-bed laboratory studies by distorting the development of the movable-bed profile and causing spatial and temporal variations in the wave height. Temporal wave height variability caused by the changing reflectivity of the developing profile complicates the study of the laboratory effects, as well as the investigation of coastal engineering problems. Temporal reflection variability would presumably be eliminated after the profile reached equilibrium, but equilibrium is difficult to define and attain in the laboratory. 1. Background. The Laboratory Effects in Beach Studies (LEBS) project (called the Wave Height Variability project until 1971) was initiated in 1966 to investigate the sources of and possible solutions to the wave height variability observed in longshore transport experiments at the Coastal Engineering Research Center (CERC) in the late 1950's and early 1960's. Three-dimensional experiments were performed in 1967 to isolate the major sources of wave height variability. The superposition of incident and reflected waves was found to be a major source of spatial variability, and changes in the profile reflectivity was found to be a major source of temporal variability. Two-dimensional tests were performed in 1968 and 1969 to study wave reflection and served mainly to develop improved techniques for collecting and reducing profile surveys and wave reflection data. During 1970 to 1972, 10 lengthy experiments were conducted to define the amount of wave height variability due to wave reflection and varia- tion in reflection. These experiments were to be continued until the profile reached equilibrium and the temporal wave height variability ceased. The effect of tank width was to be studied by conducting tests in both 6- and 10-foot-wide (1.8 and 3.0 meters) tanks. The results of these experiments have also pointed out other laboratory effects. 2. LEBS Reports. This report (Vol. VIII), the last of a series of eight volumes on LEBS, analyzes the results of the 10 experiments. The experimental conditions, facilities and equipment, quality con- trol procedures, and data collection and reduction procedures common to all 10 experiments are documented in Volume I (Stafford and Chesnutt, 1977). Data reduction and collection procedures unique to individual experiments are described in appendixes to Volumes II to VII (Chesnutt and Stafford, 1977a, 1977b, 1977¢c, 1977d, 1978a, 1978b). Volumes II to VII discuss the results from the 10 experiments and draw conclusions from the one or two experiments described in each volume. The experimental conditions of the 10 experiments are summarized in Table 1; the volume in which each experiment is reported, and ref- erence to three other studies which discuss some of these experiments are also given in the table. Table 1. Summary of experimental conditions. Other references Chesnutt, et al. (1972) | Chesnutt and Galvin (1974) Chesnutt (1975) Chesnutt, et al. (1972) Chesnutt and Galvin (1974) Chesnutt, et al. (1972) Chesnutt and Galvin (1974) Chesnutt (1975) Chesnutt, et al. (1972) | Chesnutt and Galvin (1974) Chesnutt (1975) 72A-10 5 4 \The first two digits of the experiment number indicate the year of experiment; the letters X, Y, A, B, C, and D indicate the separate volumes in the LEBS series of reports. The last two digits indicate either the 6- or 10-foot-wide wave tank used for the experiment. 2Distance from generator to the initial stillwater level intercept. 3Determined for given wave period and constant water depth of 2.33 feet, so that the generated wave energy flux had a constant value of 5.8 foot-pounds per second per foot. 3. Scope. The primary purposes of the LEBS reports are to: (a) Relate temporal and spatial wave height variability to the changing reflectivity of the developing profile; l2 (b) measure the approach of the profile to an equilibrium condition; and (c) identify, and if possible quantify, the effects of other laboratory constraints (e.g., water temperature, tank width and length, and initial slope) on the resulting labo- ratory profile. The discussion of results in Section IV of Volumes II to VII covered (a) wave height variability, (b) profile equilibrium, and (c) laboratory effects. This volume discusses those topics in Sections II, III, and IV, respectively. The data from individual experiments are not repeated in this volume, but the results from Volumes II to VII are compared to develop more generalized conclusions (Sec. V) and recommendations (Sec Vr Definitions of coastal engineering terms used in LEBS reports conform to Allen (1972) and the Shore Protection Manual (SPM) (U.S. Army, Corps of Engineers, Coastal Engineering Research Center, 1977). A definition sketch of typical profile zones is shown in Figure 1. The backshore- foreshore boundary is at the upper limit of wave uprush, the foreshore- inshore boundary at the lower limit of wave backrush (low water line), and the inshore-offshore boundary at a point just seaward of the breaker. Plots of contour movement (CONPLT plots) are used in all experiments to show, in one figure, the changes in profile shape along a given pro- file line throughout an entire experiment. An interpretation of these CONPLT plots is given in Section II,2 of Volumes II to VII. The LEBS data have other uses to both the laboratory and field engi- neer. For example, the profile surveys, sediment-size distribution data, and breaker conditions reported in Volumes II to VII, and color slides of the ripple formations (available at CERC) can be used in a more detailed analysis of coastal processes. The shoreline recession rates from several of the experiments can be used by the field engineer, after consideration of scale and laboratory effects, in determining generalized shoreline recession rates. A further analysis of the profile surveys is currently being conducted by CERC to determine temporal variations in net onshore-offshore material transport. The profile data would be use- ful in calibrating a numerical model of profile evolution. The LEBS reports are not an all-inclusive study of laboratory effects, because several other known laboratory effects have yet to be examined intensively. These reports serve as an introduction to the subject of laboratory effects and as a guide to some of the problems involved in performing movable-bed coastal engineering model studies and research experiments. II. WAVE HEIGHT VARIABILITY The nominal (generated) wave height, H,, in Table 1 is the height of the wave traveling from the generator toward the profile unaffected 13 Ge ‘(90-ALZ JUSWTIedx9) souoz e~Ttzord Fo ydeyYs uoTITUTFEq “T ean3Ty (44) ydaouajU] TMS JOUIHI4Q wos} aduDjsIG 82 I? t| l 0 L- CUS) Ss Pee aJOUS}IO: (44 OG!) ee SOUSHIO JJOYUSU| aJ0ysaso4 = GLE a= = 1) OG J91JV S2l1JO1g yooag (44) TMS e@Arogo uoljDAa] 3 14 by reflection, wave instabilities, or tank oscillations. This wave height (referred to as the generated wave height in Vols. I to VII) is assumed to remain constant as long as the generator operates smoothly. Wave height variability is any deviation in wave height from Hc. This variability can be spatial (the wave height varies with position along the tank (longitudinally) or across the tank (laterally)), or temporal (wave height varies with time at any point). The terms used in describing and calculating wave height variability are defined below. Variation in wave reflection from the profile, which is the major source of wave height variability, and other sources of wave height variability are discussed in this section. 1. Definitions of Terms. a. Operational Terms. The following terms were used in the measure- ment and calculation of wave height variability parameters. (1) Wave record--a strip-chart recording containing all the water surface elevation measurements during a given run. Wave records include recordings made with a stationary gage or a slowly moving gage. (2) Crest and trough elevations and postttons--determined from wave records using a digitizer, which produced a deck of punchcards containing the (a) position (on the recording) and elevation of all wave troughs, (b) position and elevation of all wave crests, and (c) position of all tick marks relating chart paper position to stations along the wave tank. (3) Computer programs WVHTCN and WVHTC2--written to automate the analysis of wave height variability data. (4) Local wave hetght (Hg)--the difference in elevation between a trough and the succeeding crest, with its position defined midway between the two points (determined by the program WVHTCN). (5) Average wave hetght (Hy)--the average of all the local wave heights in a record (determined by the program WVHTCN) . (6) Running average wave height (H,,)--the average of all local wave heights within a standing wavelength (one-half the generated wave- length) of a point (calculated for each Hg by the program WVHTCN). (7) Running average wave height deviation (D,,)--calculated by subtracting Hy from each Hy, along the tank (plotted as a function of tank position by the program WVHTCN). (8) Amplitude of the running average deviation (Am)--determined by measuring the maximum deviations on the plot of Dy, versus tank position and averaging the absolute values ot the maximum deviations. fe) (9) Local wave height deviation from the average (Dp)--calcula- ted by subtracting Hy from each Hp and then removing any long waves or tank oscillations from this curve by subtracting the local Dy, value from each Hg (calculation is performed by the program RVEGNE which then plots Dg as a function of tank position). (10) Amplitude of local wave height deviation from the average (A)--the amplitude of the best fit size curve to the plot of Dg versus tank position (computed by program WVHTC2). (11) Reflection coefficient (Kp)--calculated by dividing A by Hy. This procedure for estimating Kp is referred to as the automated method in Volumes I to VII. A manual method for determining Kp is described in Volume I, which also contains a description of the automated method. Most Kp values in this volume were obtained with the automated method. The Kp values not determined directly by the automated method were determined by the manual method and adjusted by an amount equal to the average difference between the two methods to make the values com- parable to the automated Kp's. Volumes II to VII contain further infor- mation on this difference. b. Conceptual Terms. The following terms describe the different physical components of the deviation of the water surface from the still- water level. (1) Reflected wave hetght (Hp)--the height of the seaward- traveling waves which have been reflected from the profile. Waves are reflected from any segment of the profile where the depth change is significant; i.e., the depth change is an appreciable fraction of the average depth over a horizontal distance less than one wavelength. Thus, waves can be reflected from more than one segment of the profile so that more than one reflected wave component with the same period may be present. However, over the constant depth section of the wave tanks the various components superpose, and in effect, they become a coherent reflected wave. The amplitude, A, of the deviation of the local wave height from the average (defined above) is a measure of the reflected wave height, Hp, in the constant-depth section Of them tanks Eppes also equal to the product of Kp and Hy. Hy is defined in (3) below. (2) Re-reflected wave hetght (Hpp)--the height of the shoreward- traveling wave which has been reflected from the profile and then reflec- ted from the wave generator. This wave height is the product of H,, Ky, of the profile, and the reflection coefficient of the generator, Kpp. Since wave filters were not used in front of the generator in the LEBS experiments, Kpp is assumed to be 1 and thus Hpp is equal to Hp. (3) Inetdent wave hetght (Hyz)--the height of the shoreward- traveling wave that results from the superposition of the nominal gene- rated wave height, Hg, and the re-reflected wave height, Hpp. Hy varies with time as the phase difference between Hp and the generator motion varies. At any given time, H; is equal to Hy (defined above). 16 (4) Lateral tank oscillattons--long waves (with a period other than the period of the generator) resulting from critical combinations of wavelength and tank width, which occurred in some experiments and could not be controlled. These waves can be identified by examining the deviation of the running average wave height, D,, along ranges other than the center range. (5) Wave instabiltties--variations in wave shape, which result from nonlinear shallow-water waves propagating in the tank. 2. Variations in Wave Reflection. Reflection coefficients varied noticeably throughout the LEBS experi- ments (Table 2), and an important part of the experiments is the attempt to identify the causes of this variation. Each of the two tanks had an adjacent control tank situated so that the same generator simultaneously produced the waves in both the test tank and the control tank. The control tank had a 0.10 smooth concrete Slab instead of a movable bed. Kp variability in the fixed-bed tank is a measure of the Kp measurement accuracy in the movable-bed tank. Table 2. Average reflection coefficient and limits of values in each LEBS experiment. Experiment Movable-bed tank Fixed-bed tank Limits of Kp Avg Kp Limits of Kp j=) 0. 0. 0. 0. 0. 0. 0. 0. 0. a. Processes. Three processes are involved in wave reflection from a movable-bed profile. These are the conversion of potential energy stored in runup on the foreshore into a seaward-traveling wave, the sea- ward radiation of energy from a plunging breaker, and reflection of the incident wave from the submerged profile, particularly where the depth over the movable-bed changes significantly (Chesnutt and Galvin, 1974). \7 (1) Reflection from the Foreshore. The foreshore developed a relatively stable shape within the first 10 minutes to 5 hours of each experiment. Since the foreshore shape remained fairly constant through- out each experiment, the reflection coefficient of the foreshore probably remained constant. The height of the wave reflected from the foreshore is assumed to vary directly with the height of the wave incident to the foreshore for each experiment. Measuring the reflection from the foreshore alone was difficult, because the distance between the foreshore and the breaker was frequently too short to make an accurate measurement. Fluctuations in the measured Kp during the first 5 to 10 hours are likely due to fluctuations in the foreshore reflection. (2) Reflection as a Result of Wave Breaking. Since surging and collapsing breakers break on the foreshore they do not contribute to the reflection process separately, but rather as part of the foreshore re- flection. Spilling breakers, essentially a crumbling of the wave crest, do not involve any change in direction of the water particles, and thus are not a source of reflection. The plunging breaker propagates energy in both directions as the crest of the wave plunges into the water. How- ever, in most experiments the breaker type changed from plunging to spill- ing as the profile developed, and thus the breaker reflection is assumed to decrease throughout an experiment. Measuring the breaker Kp was even more difficult than the foreshore Kp, since the breaker reflection component is always superposed with the foreshore component and in a short distance becomes superposed with the offshore component. Estimates can be made from comparisons of the re- flection from the concrete slope, which had a breaker and no foreshore, and reflections from the early profiles of the movable bed, which had reflection from both the foreshore and the breaker but very little from other parts of the profile. (3) Reflection from the Inshore and Offshore Zones. Wave energy is reflected all along the submerged profile, but the reflection does not become significant until the profile slopes become significant. In most experiments, the profile developed into an almost flat shelf between two steep slopes (see Fig. 1). The development of these zones contributed greatly to the reflection variability and hence the temporal wave height variability. Three particular profile changes apparently caused signifi- cant wave height variability: changes in the steepness of the offshore slope, changes in the elevation of the shelf at the top of the offshore slope, and changes in the length of the shelf. Increases in the offshore slope steepness increased the reflection; likewise, decreases in the slope steepness decreased the reflection. As the elevation of the shelf and top of the offshore slope increased, the reflection increased; as that elevation decreased, the reflection de- creased. Increases in the length of the flat shelf, which was the dis- tance between the two reflecting slopes, caused the phase difference 18 between the two reflected wave components to vary. When the components were in phase, the measured Hp (in the constant-depth section) was high; when the components were out of phase, the measured Hp was lower than the absolute sum of the two reflected waves. Because the phase difference between the two reflected components varied, the amount of energy reflected from the submerged profile could not be measured. However, the effect of the three profile changes can be seen in the reflection variability of some of the experiments. b. Reflection of the 1.50-Second Wave. Figure 2 shows the Kp versus time for experiment 72C-10, the only experiment with a 1.50-second wave period. The Kp varied between 0.02 and 0.12 during the experiment, with no apparent increasing or decreasing trend in the maximum or minimum values or in the amount of variation. Minimum values occurred at 35, 60, 90, 95, and 120 hours; maximum values occurred at 1.5, 25, 55, and 105 hours. Steep foreshore and offshore slopes developed almost immediately and then began to separate as the foreshore eroded landward and the offshore prograded seaward (Table 3). As the two reflecting zones separated, the change in phase difference between the two reflected waves would have caused a variation in the measured (total) Kp. Assuming linear theory and an average depth of 0.6 foot (18.3 centimeters), an increase of 3.12 feet (0.95 meter) in the distance between the two reflecting zones (i.e., the width of the inshore) would have caused a 360° change in phase dif- ference. The distance between the O- and -1.0-foot (0 to 30.5 centi- meters) contour increased from 10 to 28.5 feet (3.0 to 8.7 meters) during the experiment. Therefore, five cycles of 360° phase-difference change were possible and if the cycle started with the two waves 180° out of phase, four in-phase (maximum) values were possible, as observed. The average Kp was 0.05 (Table 2). The seaward movement of the seawardmost -0.8-foot (24.4 centimeters) contour (Fig. 2) is an indicator of the general steepening of the off- shore zone and the shoreward movement of this contour that the elevation at the top of the submerged offshore slope dropped to -0.9 foot (27.4 centimeters). The shoreward movement of the -0.8-foot contour near the end of the experiment did not cause any noticeable reduction in K,, as was observed for -0.7-foot (21.3 centimeters) contour during tests with the 1.90-second wave (see Fig. 45 in Vol. III), but here the average Kp was already smaller than the 1.90-second wave. c. Reflection of the 1.90-Second Wave. @)) Experiment —/0X=06" The meflection) coerfilcient. iKor versus time for experiment 70X-06 is shown in Figure 3. During the first 10 hours, Kp varied between 0.03 and 0.14. At 10 to 25 hours, Kp remained fairly constant (0.08 to 0.11) and then dropped to 0.02 at 31 hours. From 33 to 45 hours, the Kp was lower, between 0.04 and 0.08, 19 0.15 (Bay) 4u9!9154009 U0!49e}40Y 0.10 0 Reflection Coefficient -10 _—— -_-— —_—— _-_— (14) sdadsajuT WMS [OUIbI4Q WoI4 edUDISIG SOS tit contour 100 150 Cumulative Time (hr) 50 10 Reflection variability and movement ° of the -0.8-foot contour in experi- ment 72C-10. Figure 2. 20 *Butttitds «= (Se “Butitids pue 8ur8untd = ‘a7 *Burguntd = dy OvT 03 O£T O£T 03 STT suot2 -BAdTeA 10430 38 Buynutzuoy *Suysvorsoep 33 £°T- 02 6°0- 28 uoyz3 ysodeq esousutT gouut jo eBpe 203n0 1a.Udd p1eMo} Buy -sseaZoid pue s{T[em apts3no BZuo,e Zuyu -uyZeq 3uyseorsut ygno132 19A0 y dag untIqTT -tnba dutyseoiddy eLOYSUT z93n0 jo e3pe 103no ‘suoyatsod 1IYvIIqG OM] um 77°90 = 0Sp upow podoyaaop y8no13 pue 1g 214815 adpo pasaeas 14/33 10°0 50 0281 38 paporg e10ysuy 20 -3no sso10e POTrBA 4OTII9ITP PiBMatoYs UZ Meld ZT OUS 3noy8no1y2 uot71sodeg pedotonap J19\us !pepora ieg e1qbIs Ig CRE Get s°T 93 49°0 £9°0 92 0 ee omyL 14/33 SI°0 JO 0381 38 paporg atquis ope p1remaroys {uoTIIeITp p1eMess Uy. M913 pue ‘pado “TOASP JFTAYS ITY aioysuy Jo a3pa 1aqno “UIT. prem -Bas BuTAoW 4F H'T- 02 6°0- 3B uoyyysodeg padotaaap 1eq az1oys3u07 adeys 2tseq padoyencg aimjviedma, 19384 SUOTITPpuod 19yxBIAIg ea10SFIO atoysuy Jeng eloysuy Iouuy a10Yysatoy *OI-9ZZ Juomysedxe uy quomdozeaop of yzord zo Arwmmsg ‘¢ atqey 2| a6 0.20 2 0 Reflection Coefficient 0.15 2 oO 0 \y @ Ez ROSE Bali : 4 \ 5 i O ra ~~vijr\~ ~— a O v \ : “Saf ne Q ° — Ms 7 74\ a S 5 O ; ite ior 1\ Q O O 0. | Oz & Pp lps MY E ro) P CD OO G& O O QD When o Ee We O®M 1/00 O OGDO orang S Bp O np ds or O O O oe Boe fe eepo SAC -0.7—-ft Contour 0.05 S ° 0) © as O f=) O 15 OQ O 50 100 150 200 Cumulative Time (hr) Figure 3. Reflection variability and movement of the -0.7-foot contour in experiment 70X-06. a2 and was very gradually decreasing; after 95 hours, Kp fluctuated be- tween 0.06 and 0.14 and, in general, increased. While Kp was fluctuating so greatly during the first 31 hours, the foreshore developed and eroded landward, a longshore bar developed, the bar and the plunging breaker moved landward and then seaward, and (after 26 hours) the offshore zone began to steepen (Table 4). All of these profile and breaker changes could have contributed to the Kp variations during that time. Between 33 and 95 hours, when Kp was less variable and very gradually decreasing, the foreshore position stabilized, the breaker type changed to spilling (and thus no longer reflected any energy), the longshore bar eroded (and thus was no longer a reflector), and the offshore slope gradually steepened at the base and prograded slowly sea- ward (and thus the phase difference between waves reflected from the two zones may have gradually changed). A change of 4.5 feet (1.4 meters) between the foreshore and offshore would have caused a 360° change in phase difference. After the shelf developed, the distance between the O- and -1.5-foot (45.7 centimeters) contour increased only 1.9 feet (57.9 centimeters). Table 4. Surmary of profile development in 2 Se 70X-06. Tine Foreshore Offshore Breaker | Breaker conditions ——_| Gater tecperature (hr) (9) Gtol developed charecteristic shupe elevation of bar increased to -0.3 ft bar moved shoreward, depth 0.3 ft ber stable (depth and position) bar moved seaward, large deposition at | 0.s depth 0.4 ft deposition at 0.9 ft depths of 0.7 and 0.8 ft large deposition P 17 to 16 at 1.1 and 1.0 ft position moving 17 to 20 seaward to 0.0-ft depth changed froe P to SP Ree ee cea Position moving 14 to 18 seaward to 0.7-ft depth sP 14 to 15; drop to 11 SP 11; rise to 15; drop to 8 stable slope 0.7-ft seiatansneTg ONG, ile tereeeeren | at seavard seiatansneTg ONG, ile tereeeeren | range 0.34 to 0.56 |0.27 to 0.33 0.26 to 0.31 -22 to 0.29 avg. 0.39 0.31 0.28 otis Ip a plunging; SP = spilling-plunging. deposition > 1.) ft avg. erosion rate of 0.06 ft/hr deposition > 0.8 ft Mahe re, 26 to 30 deposition > 0.8 fr 28; drop to 18 22 to 26 | avg. erosion rate of 0.14 ft/hr deposition at 0.8 ft position of bar stable, depth varied 0.3 to 0.4 ft deposition at all depths SkL stable erosion Bee at of last of scarp 0.5 and 0.6 Bee fill started bar eroded erosion at erosion of 0.5 ft fill << avg. erosion < avg. shoreward edge stabilized for remainder erosion >> oenoee seaward edge stabilized for remainder deposition >» 0.9 aie erosion formed deposition at steeper slope 0.6 and 0.7 ft 17s (median grain size in mm) 2® After 85 hours the seaward movement of the -0.7-foot contour in Fig- ure 3 corresponds to the steepening of the upper part of the offshore slope and that roughly corresponds to the increase in Kp after 95 hours. The large fluctuation in Kp did not result from any apparent profile change, but the general relationship between the -0.7-foot con- tour and Kp did exist. (2) Experiment 70X-10. Kp versus time for experiment 70X-10 is shown in Figure 4. During the first 20 hours, Kp varied from 0.07 to 0.12, and between 21 and 89 hours, Kp ranged between 0 and 0.08. From 89 to 174 hours, Kp increased from 0.04 to 0.14 with a maximum of 0.15 at 139 hours. After 174 hours, Kp decreased, to as low as 0.06 at 204 hours. The higher Kp values during the first 20 hours occurred while the foreshore developed and eroded landward, a longshore bar developed, and the bar and the plunging breaker moved landward (Table 5). Between 21 and 89 hours, while Kp was lower but gradually increasing, the fore- shore and the bar moved landward, then the foreshore stabilized and the bar eroded. During the same time the breaker moved seaward and changed to plunging (at 70 hours), and the offshore slope slightly steepened and prograded seaward. The distance between the O- and -1.5-foot contours increased 2.2 feet (67.1 centimeters), enough for a 180° change in phase difference between the two reflected wave components. The gradually increasing Kp after 21 hours followed the general seaward movement of the -0.7-foot contour (Fig. 4), but individual Kp fluctuations were not directly relatable to the movement of this or other contours. The increase in both Kp and Kp variability between 89 and 174 hours occurred while the foreshore was stable, the breaker was spilling (no reflection), and the offshore was gradually steepening. (3) Experiment 71Y-06. KR versus time for experiment 71Y-06 is shown in Figure 5. During the first 10 hours, K varied from 0.01 to 0.10. Then, for 115 hours the Kp remained relatively low, ranging from 0.01 to 0.07 with most of the values near 0.05. For the remainder of the experiment, Kp increased in mean value and in variability, varying from O5605 0 0624. The higher Kp values during the first 10 hours occurred while the foreshore zone and longshore bar were developing and retreating landward (Table 6). Between 10 and 125 hours, when Kp was low and fairly con- stant, the foreshore zone and longshore bar.were retreating landward and the offshore zone was prograding seaward but did not steepen.. After 125 hours, when K, was increasing and becoming more variable, the foreshore zone éontinued te erode, the onshore zone developed into a flat shelf with the depth over the shelf varying between 0.7 and 0.8 feet, and the offshore zone became steeper and continued to prograde seaward. Some variations in Kp were related to the movement of the -0.7-foot contour (Fig. 5). The general seaward movement of the -0.7-foot contour 24 -10 0.20 -0.7 — ft Contour = 0.15 a i> avg. 140 to 150 eee oe eis 160 to 170} rate of fill << avg- 170 to 190] rate of fill = avg. “a Lame | 200 to 210 Tate of fill << avg. 200 sand 0.29 to 0.68 0.27 to 0.50 samples mean (mm) \p = plunging; SP © spilling. 7R © breaks first along range 1; C = breaks uniformly across tank. still extending seaward; lateral variation in depth R-l, 0.6 to 0.7 fe; further erosion along ranges -l and -3 0.26 to 0.33 26 R-9, 0.7 to 0.9 ft , deposition between depth of -1.0 and -1.5 ft deposition at -1.0 ft deposition at -0.9 and -1.0 ft depositaon at all depths except -2.0 and -2.1 ft along range -1 deposition at all depths contours stable for -1.0 to -1.5 ft; ft; depus:tion below -1.5 ft Breaaser conditions Depth (tt) tecperature Cc) JU91914ja0) U01y9a19Y “QO-ATZ }USWTIOdxe UT In0jUO0D 00F-7°0- 942 FO JUSWSAOM puUe ALT[TGETICA UOTIDIETFOY OOv O SOO O10 G!0 020 G20 °g omnsty (44) awiy aatyoynwng Os¢ oo¢ OS2 002 OG | 00] OS 0 G2 O O “ 19 O ©) o|| ° \ OW O O r a O O o) © O Q Od O iS © O R e 0 O Tt ROPER of 00 © o O02 O 0 GRAS @) i O 0 0 O O) OO 0 \ ‘ il QO vn oi oW oie E ih O 0 A O O n~ ! \ O O O G| KY '\ O O \ I WR AG O \ i \, = oT) , | ‘ O A \ a " rt V4 i J \ | 2 Ol Vey \ / O \\" | 4 \ , ES | \ ix ‘eae VAN SSN 1 ale as ea PBN eRe eons oY weary aces ia ivan een ENR N OG Nae \ ! O \ / N } L? INOJUOD 33-1 O- S \ ! ! O 1, é \J JU9191}j909 uo1j9a}}9y (43) ydaosayuT TMS JOulbI4Q wos) aduD}sSIg 2? syadep Ile 2e uotz1sodaq aR Nm OB 6°0- SUuOTEASTA We Ajysou uot itsodaq sujdep [Te 12 A{w1oztun uot i1sodaq aLOYSUT Iouuy suotj.e1Tp yOq uT yqBuet ut meas sT9YS alee Gee Ces GOH SUOTJPADTO 3B Ajisou uotztsodaq padorerep x19uUS pieneas aF 8'O- pure} L°O- 28 uotztsodap | "IF 9°0- 3B UOTsSOIg £7 syadep Tre ae Ajw1oztun uot tsodaq { pZ 03 2 | pZ_02 61 SUOTIBACTA 12 Atqysow uotztsodeq *L°0- ‘9°0- suota | -BAaTO YB UoTITSOdaq I 43 ZI- 03 6'0- | L 61 ear a ainzetedusa} 1322 [sea | worrsoa | Ga) eo] | aLOUss30 “QO-ATL JUaUtzodxe ut quaudoterap arryoid zo Areumins azoysut 101n9 | edots dears ATITeJ PIUTeUTeW pepore reg 1y/3F 8I0°O FO eel Ye pleMaroys peAom req [1F p°0- pue ¢'Q- usemM20q pet1ea eq FO uoTIeAITA 1S9ID powtoz 1eq a1oyssu07] atoysut Louuy 79 9TqeL ‘Buttitds = ¢ ‘{8urBuntd = d_ 0 S 0 0 01 STE 0. ae eee peed SLE be iS% SZ 0zZ 002 8 SL so T_03 SZT | T 03 SOT eae ST 92 OF A ae (ay) ewty ty/3F SZ0°O uoTtTsols JO ale aBe19Ay Iy/IF CTL*O uotsore JO o3el a8e1aAy padoyaneap adeys ITST19jdeIeY) artoyselo4 28 indicates the steepening and increasing of the reflectivity of the off- shore zone. The highest Kp values, at 235, 320, 360, and 375 hours, occurred at times when the -0.7-foot contour was at its seawardmost position; low Kp values at 195, 240, and 340 to 355 hours occurred when the -0.7-foot contour was at more shoreward positions. An exception to this occurred at 270 to 275 hours, when the -0.7-foot contour was in a seaward position and the Kp was low. At other times the relation- ship existed, but the variation was not as great. The continued separation of the foreshore and offshore zone would have caused the phase difference between the two reflected waves to vary ” and the measured reflected wave to have a long-period variation. After the shelf developed, the distance between the O- and the -1.5-foot con- tour increased 8.6 feet (2.6 meters), enough for two cycles of phase- difference change, which may have contributed to some of the long-term Kp variation. (4) Experiment 71Y-10. Kp versus time for experiment 71Y-10 is shown in Figure 6. During the first 10 hours, Kp varied from 0.05 to 0.11. Then, for 195 hours the Kp remained relatively low, varying from 0.01 to 0.08. For the remainder of the experiment, Kp was generally higher, varying from 0.05 to 0.13. The higher Kp values during the first 10 hours occurred while the foreshore and longshore bar were developing, the breaker was plunging, and the foreshore was eroding (Table 7). Between 10 and 205 hours, while K was low, the foreshore retreated at a rate of 0.016 foot (0.5 centi- meter) per hour, the bar was first stationary and then eroded, the breaker type changed from plunging to plunging and spilling, the inshore developed into a long, flat shelf, and the offshore zone gradually steepened. The Kp was higher, after 205 hours, when the inshore zone had fully devel- oped, the foreshore was eroding and the offshore prograding. The dis- tance between the O- and -1.5-foot contours increased 7 feet (2.1 meters), enough for a 560° change in phase difference, after the shelf developed. Variations in relate only generally to the movement of the -0.7- foot contour (Fig. &. i.e., the Kp increased about the time the -0./7- foot contour began moving seaward with the prograding offshore zone. The development of the profile in this experiment varied laterally, the devel- opment of the shelf began first along one side and progressed across the tank. This lateral variation in development obviously created a lateral variation in the profile reflectivity. Although this variation could not be measured by the one gage in the center of the tank, the variable pro- file reflectivity certainly contributed to the variations measured along the center of the tank. (5) Experiment 72D-06. This experiment varied from the four other experiments with a 1.90-second wave in having an initial slope of 0.05 rather than 0.10. The Kp versus time for experiment 72D-06 is shown in Figure 7. During the first 15 hours, Kp varied from 0.04 to 29 ‘OT-ATL JUSWTIEedx9 UT INOJUOD }OOF-/°O- SY, FO JUSWOAOW pue AIT[TqGeTIeA UOTIIOTFOY °9 OINdTY (4y) awiy antyojnwn9 OSE OO¢€ OS2 002 OS| 00 0S 0 ° = 02 O O 5 } en S) juala! 43209 ss eye fe a 0 DQ O O) O | a vo1}99]494 , ; . We GOO ows d \ e " 0 a. al O LO - 2 ae x ~~ sf Ne re db as . O Xe = = O O = Oe a v oF M CD al LO | 5 ae INE 3! O Y R C A O i ° S S : I 0 a= SS) O One \ mn ; ry XN I A = 2. 0 | 0) b i Sa \g O hod q Ol a an O \ } OU IG\ rr hs Be 4 : = =n 4 so / vVisy WS “1 =e SN tn ery van ven = =. 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SSOLIG Patiea Woyssadar sutTparoys sammoy S{z 38 1 oBuvxz Buote Suypue pus samoy SI—T 38 6 oduex Buoje ZutuuzZeq yuez $soldB possaif01d uewdoTeaep 3x1 04S Smmoy O6T 38 I eSuez Buote pue SImoy STT 38 6 a8uexr Buoje ueseq ieq JO uoTso1g TU/2Z 9T0°0 38 yuez ssordB BIOZ{TUN UOTSSOI01 OUTTOIOUS 3 F°O- 02 v'O- BIZ POFIVA UOFIVAGTO 3SoId {A4zeu013836 18g 1Y4/3Z CET'O Ie yuv3 s60190 wI0Z;uN UOySS0I21 OUTTOIOYS 33 8°0- pus *L°0- ‘9°Q- suoya -BAOTO 3B UTI} S0d0qg ST 023 OF pedojaaap adeys dT 3stTi9j.e1ey) ja e10ysaioy (44) amyy paulroz 1Bq e10ys8u07] eIOYSUT 103NO 3| 0.30 Reflection Coefficient O SS 0.25 -0.7-ft — \ | = 6 ! 0.20 my | a a | c ® | @ u A Oo iS I | = c Ha | ‘o — ) ) | fo) ZO (@) IS2 = \ fi l S 1X! 1 S ro) flora i ® £ i = oO } | | rea ie | hee | © ISR Pe whl 0.10 N ( \ | 9) So a ! \ | of ay ! \ rie oO \/ Us OY v NEN \ o v rr) | AO \ a fF 0.05 \ I \ \ \ Kael \l 25 : (@) O 50 100 150 200 Cumulative Time (hr) Figure 7. Reflection variability and movement of the -0.7-foot contour in experiment 72D-06. 32 0.08. Between 20 and 130 hours the Kp was higher and highly variable, varying between 0.08 and 0.27. For the remainder of the experiment, Kp was lower and less variable, varying between 0.07 and 0.10. The lower values during the first 15 hours occurred while the fore- shore developed (slower than in the other four experiments) and began retreating, the longshore bar developed and then eroded, and the breaker type was strictly plunging (Table 8). Between 20 and 130 hours, when the Kp was high and varied greatly, the foreshore was retreating (except for advancing between 125 and 130 hours), the breaker was mixed between plung- ing and spilling (indicating minimal reflection), the inshore was becoming longer and flatter, and the offshore was steepening, particularly after 95 hours. Between 135 and 180 hours, when Kp was smaller and less variable, the foreshore was stationary, the offshore zone continued to prograde seaward, and the inshore zone changed from an almost flat shelf with an average elevation of -0.7 foot to a flat region at the seaward end of the inshore (elevation -0.8 foot) and a trough at the shoreward end of the inshore (elevation -1.3 feet). Some Kp variations after 100 hours, when the offshore slope was a significant reflector, correlate well with the movement of the -0.7-foot contour (Fig. 7). When the -0.7-foot contour was at a more seaward posi- tion, Kp was high; when the contour moved shoreward, Kp was low. The Kp reached higher values quicker than in the first four experiments, even though the initial slope was flatter. This earlier high in Kp may have been caused by the earlier seaward movement of the -0.7-foot contour in this experiment. The Kp was measured over the inshore shelf several times between 100 and 155 hours and varied between 0.06 and 0.12 (see Vol. IV). This measurement included reflection both from the foreshore zone and from the plunging breaker near the toe of the foreshore. The distance be- tween the O- and -1.5-foot contours, after the shelf developed, increased 12.4 feet (3.8 meters), enough for more than two 360° phase-difference changes. (6) Summary of the Five Experiments. The average Kp in each of the 1.90-second experiments with the 0.10 slope (70X-06, 70X-10, 71Y-06, and 71Y-10) varied from 0.07 to 0.09 (Table 2). However, in experiment 72D-06 with the flatter initial slope, the average Kp was 0.12, much higher than the tests with the steeper initial slope, con- trary to the hypothesis that as the ratio of the wave steepness to the slope steepness increases, the Kp, decreases. The close correlation between the -0.7-foot contour and Kp variations in experiments 71Y-06 and 72D-06 suggests that the elevation of the top of a steep, submerged slope can be as important as the steepness of the slope in determining the Kp. d. Reflection of the 2.35-Second Wave. (1) Experiment 72B-06. The Kp versus time for experiment 72B-06 is shown in Figure 8(a). During the first 10 hours, Kp varied BS) wm ¢7'0 02 6I'0 = 0Sp v40 03 2°0 8°0 93 2°0 om iz" tt Ol IT £°0 03 :9°0 £°0 93 9°90 emesodvay 29104 BUOFIFPUOD 29dyed14 °90-0Z7Z Juowtiedxe ur 33 B°O- 38 Uotatsodap {33 €°1- payees OT UOTI8IS Ie9u UOTsSOIZ 33 8'0- 38 Uoya -ysodap $13 {'0- 38 uotsore yuertzyusys 33 6°I- 2A0ge suoTIeAa[a I{@ ye uozatsod ~ap duro tusis Q@ uoT3IeIS 41au UoTsoIA 133 8:0- 38 ATurew word -1sodop panutju09) 33 8°0- pue Z'0- uotiysodop afi07 ——{ ww 27°0 93 07° ay L°0- 4e uotaysodep afiey 0 92 07'0 = Sp aZsit- 03 6°0- Worz suotatsodap o81e] ¥ L°0- 320 uoysol1d a81e7] JF 9'O- 3B UOTsoIT ay L'0- pus 9°0- uaanzaq BurArze. JOYS 19AO UOTIBAS -[2 fo%ueys yonw Jon Sat) SMNOIBA Ie YJ S°T- puw ‘py t- "E°L- 38 Aturew 33 8°0- pue ‘uotatsodap auos L'O- 38 uoritsoday mu 97°0 03 LT'0 = 9Sp adury> on U0 y2 ;sodaq 0 = Sp a1oysa10; yatm Butgearie1 ‘odors daaas Apatey ‘votso1y "Burttyds e S {3ur3unid = dy Ost °3 Ort mm 2Z°0 93 0Z'0 = Sp 21qu3s a10ysai04 aoueape QuT[210ys ‘vols; sodag um {7°09 03 97'0 = OSp 34 $6 03 SB [sen | §4 91 59 09 01 Sf ry/dz S0°O 30 23e4 uotssazas autparoys !uoysorg 4 6°0- 3® uotitsoday 13 8'0- pue ‘7°9- ‘g'Q- 38 UOTITsodag 21045350 e10ysuy 103n9 quaudorenrep attzoid zo Areuums Pepora seg eTquis seq 18q JO yUoudo[anag asoysuy souuy ya3usy pues edots emragty -ynba jo yuaudo( arog 91°0 93 0 0104s 2404 “8 eTqeL (HM) yua1siyya09 uolsralyay wo (2) wo (©) wo Ss ~ ve = ° n ro) ro) fo} ro) fo) ro) = ro = ro TS i Nn = — reas o o wNon FT o o ont o OO N ao) COCO CO ro) o - -- —--—-~n w i) i) 1 ' i} 11 i} | ' (eo) °°, wo — = Cc ao (>) = ane fo) rt) ro 9 oO — E & a = —— S = 2 _— (o) Ss (o) w. oo @ ol = Ss : Sl 2 = Los SS (| LT o co) rey Oo wo oO Ye) ro) Ye) fo) 7 1 _— _- N N m (43) JdaosajuT TMS [0u1614Q wWosy adUuDjsIG (434) yuarsijya09 uolpoajay a) fo) rey ro) Ye) = S 7 iz 2 a fo) co) ro) ro} ro} fo) a = (@) =) ro) ) oO —_- _ qe; = i Qe Oe & SEI) CT ST Os Oo coccodd O00 — — aa 1 00 0 D0 0 i) i} [@) nm —h— (Ss oe 2 oO = ° = ° oO Cc ) ro) _ wo oO \ S3 2 i 0 we CDSE c=. a d lS ares 4 Oo ro) o Oo rey O° wo ro) 7 | N ~N ine) (49) JdaosayuT TMS [0U!6149 wos adu04s1q 35 Cumulative Time (hr) b. Experiment 72B—10 Reflection variability and contour movement in experiments with a 2.35-second wave. Cumulative Time (hr) a. Experiment /72B—06 Figure 8. over the widest range, between 0.04 and 0.15. Between 10 and 150 hours, Kp fluctuated (maximum 5-hour fluctuation of 0.06) about an increasing mean, reaching peak values at 125 and 140 hours. The major profile adjustments in Figure 8(a) and Table 9 were the development of an equilibrium foreshore and longshore bar and steepening of the offshore zone just below the inshore zone. These adjustments occurred during the first 10 hours when Kp was fluctuating greatly. Between 10 and 150 hours, when Kp was gradually increasing, the only profile changes were the gradual steepening of the upper part of the offshore zone and the seaward movement of the offshore bar (crest eleva- tion of -2.1 to -2.0 feet or 64.0 to 61.0 centimeters). The steepening of the upper offshore most likely caused the increases in Kp. (2) Experiment 72B-10. The Kp versus time for experiment 72B-10 is shown in Figure 8(b). During the first 10 hours, Kp in- creased from 0.13 to 0.18, and then between 15 and 35 hours, Kp varied only between 0.12 and 0.13. At 40 to 90 hours, Kp was higher, fluctuat- ing about a mean of 0.16. Between 90 and 100 hours, Kp increased from 0.16 to 0.24 and then fluctuated about a mean of 0.21 for the remainder of the experiment. The increasing Kp during the first 10 hours coincides with the development of most of the profile features: the steep foreshore zone, the flat inshore zone, and the flat region near station 10 in the off- shore zone (Fig. 8,b and Table 10). There was little profile change between 15 and 35 hours when the Kp was low and almost constant. At. 40 to 90 hours the elevation of the flat region near station 10 gradually increased while the Kp was higher and more variable. Between 90 and 100 hours, when Kp increased by 0.08, a longshore bar was forming be- tween ranges 1 and 5. The high values of Kp at the end of the experi- ment (after 100 hours) occurred while slopes near stations 20 and 14 were steepening. (3) Summary of the Two Experiments. These experiments with the 2.35-second wave are compared in Volume VII. The average Kp in experi- ment 72B-06 was 0.08 and in experiment 72B-10 was 0.17 (Table 2). The gradual steepening of segments of the offshore zone appeared to be the primary source of long-term Kp variability in these two experiments. The development of a more convex offshore region with several steep sections in experiment 72B-10 and a more concave offshore region with only one steep section in experiment 72B-06 possibly explains the lower Kp values in experiment 72B-06. The distance between the foreshore and offshore zones changed very little, so that the Kp variability was not a result of phase-difference changes between reflected wave components. e. Reflection of the 3.75-Second Wave. (1) Experiment 72A-06. The Kp versus time for experiment 72A-06 is shown in Figure 9(a). The Kp dropped from an initial value 36 wu ¢Z°Q = 9Sp ueaw) zy OST 3 Z°Z- 02 O°Z- 38 uoTITsodap $43 L°I- 02 ¢'T- 28 uotsosg 6Z 93 12 ' OST 02 06 6Z 02 £2 Ea TE 02 OF ies [ (0,) ainjeiedues wu ¢Z'0 = 9Sp ueaw] IYy OOT uu TZ7'O = 9Sp ueew] ry 0s YW 7°2- pue [°Z- 3e uotiytsodap $3y L°T- 02 ¢*T- 28 uotTso1g aduey>d ON 06 °2 OT soBuel JUeLeszIp Buole sowtz 33 TI JO doueApe [e202 193;e quelassIp ie 4Z p'O- pue | uotztsod umtiqt{tnbe payseoy 01 023 § €°Q- usaeMjzoq petzeA uot pepergo0id sutteroys ‘VF F*T- 02 L*0- 28 uoTsorg -BAZTSA 4YSeID Ieq foesueyd ON poewloy 1eq eLoyssuocy fedeys untiqtttnba pedoteaeg |} 91°00 02 0 saueamne pu exonsesg | —-oroussy0__—=—S«Y SSCs Sino Sd ‘90-dZZ Jueutzedxa ut quaeudoyeasp attzord zo Azemums ‘6 9TqQeL SIeyeeI1q eptsino psAow IaAdU 9UuoZ IayxeaIq opts -UT sqoq {suiejjed uot -®[NIITI e[qTuUIedsTp ou $13 7'0 02 ¢°0 Jo syadep 3e Burzguntd sioeyeorg I Cht= Pus Tiz= 32 uotztsodap faroysut moyteq asn{ odors daaqs powzos 37 uu 61° = 0Sp ueey wm 77°90 = [Sp ueay wm ¢7'0 = 9Sp ueay} ry OST uotz1tsod UT SUOTJETIVA [BI9IBT a21B, {ZutTnutjuod uotssazay La SZ 02 61 O£T 02 STT STT 92 OOT OOT 92 06 06 92 SZ SZ 92 OL OZ 02 S9 S9 02 OT (6 pue ][ saduer) WF S°O- 93 £°0- qe Butzguntg YW 8°I- MOT9q UuoTITSOdap ou {BuIstl [T™3S OT uot -83S Ivau UuOTIeAZTY (g a8uer) aF v'°0- 02 Z'0- 38 Buttttds Sutnutjuo0s Z uOT}eIS Ie9U Bale Yel} Jo uorso1g 1y/3F 810'0 $93¥I UOTSSed01 eUTT9L0YS ul 61°O = 9Sp uve wu 7Z°0 = 9Sp urea uu _pz'0 = 9Sp uvay} zy sot pue ‘¢ ‘s soBuel JO Japio ut ¢ uoT}eIs 3e powsos Ieg 7 ¥'0 'SIY OOT 28 UOTSseder 20N 6 pue £ sasuer Buojte paryetduos z uotieIs ieau 1eq JO uoTsole pue [ sosuer Juore YsiItz ‘Zutpors ueseq 7 uoTJeIS IBaU eae 1eTY ¢ pue [ soduel SuorTe yy git- MOT9q uoTIISOdap ‘foauTz yore 3e aduel YIM PetieA pue asuet yoea 32 owt} YIM pesearo -UT QT uoT}eIS IedU Bale 4eTJ JO UuOTIBADTY STTB@M yued 0} [eWLOU BuUTWODeq aUTTeI10YS ZL aBuer BuoTe padoy,aaep S u0T}B1S Le9U BOIe 1eTY 6+ uoTIeIS wu 17°90 = 0Sp uvow wolj piemeas pue /+ uoTjeIsS WwOoIZ pleMaioys PaAaow sqoq woi}0q fauoz Iayeeiq OjUT peaow Ft padkeqs pue s{T+ uot eqs woij piemaroys PaAou sqoq 92ejams wu 7Z7°0 = Sp ueow! 24 0S 6Z 02 $2 Erie s pue ‘T ‘¢ sasuex JO Iepzo ut Butpois uedoq Zz uotieIs 1e 1eg (6 pue [ seduer) #F S*'0- 02 £°0- ze Sur8untg Ss pue *¢ *T saBuer ‘g uotl -81S Iegau powsrozy uotse1 WTF {G uotqieIs ‘6 aBuer - Tg 03 OF {paArtesqo urtejjed pue ‘a8pe roddn je 38 pue *Z uotieIs Ie3uU 02 [eBwWiou Jou sUTTerTOYS 18 _Burtsuntd | ie UOTAEINIITD ON pedoteaep edots deais pauitos 1eq artoyssu0y fedeys atqeas pedozaaag | 91°09 02 0 "OI-dZZ yuowtsadxa ut quoewdozeraap attzoid jo Aremums ‘OL eTqeL YJ 8'I- MOTIq T aBueL Buorte uotqytsodap ‘oT uoTIeIS 3B bale eI (g eBuer) a v'0- 93 Z°0- STIeM yueQ 38 juaid1jja09 uo1y2a/39ay OG! GOO 020 G20 O£ 0 SE O “OARPM PUODIS-G/°S eB YITM sjUoWTIedxa UT SINOJUOD TBITITID FO JuoWwsAOW pUe AIT[TQETIVA UOTIIOTFOY *6 DANITY Ol-V2_ juawisadxy 90-V 22 JUawisadx3 D (4y) awiy aaryojnwng (44) awiy aaljojnwng 0O| OS O OSI 00! OG O O02 010 | (o) re) (43) sdaosajuy TMS JOUIB14Q Wosy aduUDjSIG (43) 3daosajuT TMS JOuUIB14Q WOs) aduDjsIg S10 Ps) @ @) © 020 = =) (2) (2) © WS- =S20 as (e) : S 2 “s=s~-=mdQ | - ogol Se J ---$--Io)- $32 1- — }}60-—— 4480 atafelstotaieres 13071 Sosass Jnoyuo) 39 of 0.24 to 0.18, then to 0.17 at 3 hours, and then began to increase, reaching 0.30 at 25 hours. Between 25 and 80 hours, Kp remained high, fluctuating between 0.25 and 0.31. After 80 hours, Kp started to decrease while continuing to fluctuate, and was 0.22 at the end of the experiment (135 hours). Within the first 5 hours the foreshore developed an equilibrium shape, which was steep along range 5 and quite flat along range 1 as a result of the counterclockwise flow pattern of the wave uprush and backwash (Table 11; Vol. VI). Since the waves broke on the foreshore, most of the wave energy reached the foreshore; as the foreshore became steeper, Kp in- creased, except at 1.5 and 3 hours. At those times, the erosion and deposition patterns at the base of the foreshore (-0.2 to -0.9 foot or 6.1 to 27.4 centimeters) were reversed and Kp reached its lowest values. An almost flat shelf developed during the first 10 hours in the inner offshore region, caused by the erosion at the toe of the foreshore and deposition in the outer offshore at depths from -1.3 to -1.6 feet (39.6 to 48.8 centimeters). As the foreshore eroded landward at a rate of 0.015 foot (0.46 centimeter) per hour and the outer offshore slope steepened and prograded seaward with déposition at the higher elevations, the shelf on the inner offshore grew in length in both directions and a bar and trough developed. During this period of greatest profile develop- ment, Kp rose sharply, reaching a maximum at 25 hours. As a result of the high reflection, a significantly large standing wave developed, with antinodes at the foreshore and station 18, over the steepest part of the profile just seaward of the flat shelf. Between the first two antinodes of the standing wave, over the flat shelf of the inner offshore, a clock- wise circulation pattern developed, apparently driven by the counterclock- wise circulation in the foreshore zone. Apparently, the circulation over the inner offshore moved the sand to the edge of the shelf, but the lack of current movement through the antinode prevented further transport and thus increased the steepness. Between 25 and 70 hours, while the profile changed 3 feet (0.9 meter) in the length of the shelf between the two reflecting zones (foreshore zone and submerged offshore slope), K, did not increase or decrease Significantly, but fluctuated over a range of 0.05. Part of this varia- tion, which was greater than the 0.02 maximum variation in the fixed-bed tank, may have been caused by the 90° change in phase difference between the waves reflected from the two slopes as they separated. After 70 hours the seaward edge of the shelf began eroding, moving landward, even though the foreshore was still retreating and the off- shore was still prograding. Simultaneously, the clockwise circulation pattern over the inner offshore began disintegrating and Kp began decreasing. By 100 hours the bar had eroded and the trough had almost filled completely. From 15 to 100 hours the outer offshore steepened, with deposition at the upper elevations and erosion at -2.0- and -2.1-foot elevations. The eroded material was moved seaward to form a bar over part of the concrete bottom. 40 wa 0z"0 = "Sp ueay ma 1z°0 = °Sp ueay ssaudoays ¢ a8uez Buorte adaoxa U} OSBaztoap 03 ado[s | AleuoTIeISs a3Da pieMatOUS Buysned ‘33 Z°Z- 02 L'I- p1es ae uotarsodep {33 s‘{-|-az0ys 3utaow a8pa prexcas 03 Z°I- 3B UoTSOIg fuorgaz Butdots ATuag Pesnzuods seu0jeq pue ‘uxop syPreiq Sapouyaue Z 3S1T; WaeNI9q LOTSE[NIITO ut 1810USa10; PATITZ y3no13 ‘papors req uo uot Ie[NdI19 uadeaas {pienatoys supzAow uesaq 14/33 ¢10°0 aSTMYIOTD 03 edoys Butsne) J19YS JO adpa pieneas JO ajer iy wa ozo = °Sp uea; ms 97°09 = “Sp _ueay 0 wu QZ°0 = a) UB Wr 027°0 = Sp ueay IF 1° 93 0'°C- 38 UOFSOIS £33 6°I- 02 ¢°T- 3e uoTItTsodaq pedoyaaap y8no13 pue adoyaaua 1eq {SUuOLIIaITp YI0q plespuey aaen Butpuras Uy YaBueT uy Maz3 ZT ays pareariay JO sapoutque Zz 4sIty Q1OYsoI0; usaszaq UOTIE[NIITI }30 axed LeMOT ASTMYDIO[D fa10ysa103 uo Butyeaiq to LOT Je[NIITO 4Zuysde {oo 33 9'I- padoranap @STayso[I1a4uUNOD 20 But3ing | 03 §°{- 3B UuoT3;sodag Jays 2e1JZ Ysouye uy edeys antaqttynba Ppedo[aasg (9.) einzeszadza3 223ey $3ua1in) Sioyeoig eroszzo 102NO aIOYSJFJO JOUUT astouse104 *QO-VZZ JuaWtsedxe ut juowdoTaaep attzoid zo Arcuums ‘TT eTqeL 4| Between 100 and 135 hours the foreshore continued to retreat, the inner offshore became a gently sloping region, the outer offshore slope steepness decreased, and Kp continued to drop. The movement of the -1.2-foot (36.6 centimeters) contour in Figure 9(a) is an indication of some of these profile adjustments and correlates well with Kp variations. The -1.2-foot contour moved seaward at 15 hours and Kp began rising. After 70 hours the -1.2-foot contour began moving shoreward, as the inner offshore eroded and the outer offshore slope became less steep, and Kp began to decrease. (2) Experiment 72A-10. The average Kp for three ranges versus time for experiment 72A-10 is shown in Figure 9(b). The Kp dropped initially to 0.24 and then began a gradual long-term increase, reaching a maximum of 0.37 at 55 hours. Between 60 and 80 hours, Kp varied between 0.31 and 0.35. During the first 1.5 hours the foreshore developed a steep slope and within the first 10 hours an almost flat shelf developed in the inner offshore region (Table 12). From 1.5 to 25 hours the foreshore prograded 0.5 foot (15.2 centimeters), beginning first along the outside ranges. For the first 20 hours sand was deposited in the outer offshore at depths from 1.2 to 1.5 feet; from 20 to 25 hours sand was eroded at depths of 1.6 and 1.7 feet (48.8 and 51.8 centimeters), thus forming a slightly steeper slope on the upper part of the outer offshore. During this initial profile development, Kp rose sharply. After 25 hours the only profile changes were a slight general in- crease in the foreshore slope and a gradual increase in the foreshore berm-crest elevation. The Kp continued to increase, but at a slower rate. The short-term variations in Kp after 35 hours was +0.03, on the order of the +0.025 variation in the fixed-bed tank. Throughout the experiment the foreshore slope was slightly flatter along the outside ranges and Kp was significantly lower along the outside ranges. The movements of the +1.0-, +0.9-, and +0.8-foot contours in Figure 9(b) indicate the gradual increase in the foreshore berm-crest elevation which apparently caused the increase in Kp. The distance between the foreshore and offshore did not vary. (3) Summary of the Two Experiments. The average Kp in experi- ment 72A-06 was 0.26 and in experiment 72A-10 was 0.30 (Table 2). The elevation of the top of the submerged offshore slope appeared to be the primary source of long-term Kp variability in experiment 72A-06. The gradually increasing berm-crest elevation appeared to be the source of increasing Kp in experiment 72A-10. The development of a steeper slope and higher crest in the foreshore in experiment 72A-10 explains the higher Kp in that experiment. More details on the 3.75-second experiments are in Volume VI. 42 27° 0s on 08 ma 77°09 = "Sp uray wu 61°0 =. p uBow Zu 08 uu ozo = "Sp ueay um 72°09 = 2°p ueayy | ZY 0S SZ 93 2 uotztsod pus adeys 08 03 Sz asusyd r0Cew oN | UT MMTIqt{ {nba uy dw L°T- pus 9°T- 38 UoTsoOIg nears IBq JO UOTIeAITS aptsino 8uore Buyuutseq ‘33 $°0 Pieavas padueApy UT suOTIeTIRA Ee T8l9IB{ IouyW auos az10ysazoz jo yzred $pezinds0 sazueys Zeno, uo 3ursde{j{oo. 10 QuUBITFTUsIS ON ZurZins sem 1ayeaI1g ysatz sa8uez Ppedotaaap squazins 33 §°I- 02 2°T- parzerauas-anem jo 38 uotaysodag | padorerap 3zioys adeys IZ 02 gf | Ureazed arqtuxaostp on IBTZ YAsoure uy mntiqtttnba pedotaaeqg | $°t 03 0 (3.) amnqezodmay Silayeaiq pue sjuating @1OYSJFO 191NO aLoyssJO Iauuy aioysaloy ‘OI-VZZ Jusutzedxe ut yueudoteasp attzoid jo Aremmms ‘ZT oTqeL 43 f. Summary. The Kp results from the 10 experiments are summarized in Table 3. For the two experiments with a wave period of 3.75 seconds on an initial slope of 0.10 the average Kp was 0.28; the difference between the two experiments was caused by a current pattern which devel- oped only in experiment 72A-06. For the two experiments with a wave period of 2.35 seconds on an initial slope of 0.10 the average Kp was 0.125; the difference between the two experiments was caused by a trans- verse wave which occurred only in experiment 72B-10. In the four experi- ments with a wave period of 1.90 seconds on an initial slope of 0.10 the average Kp was 0.08 for each experiment. In the one experiment with a wave period of 1.50 seconds on an initial slope of 0.10, the average Kp was 0.05. These results support the following hypothesis: as the wavelength decreases (or the wave steepness increases) on a given initial profile slope, Kp decreases. The Kp would then be expected to decrease if the initial profile steepness were decreased for a given wavelength. However, the average Kp in the experiment with a wave period 1.90 seconds on an initial slope of 0.05 was 0.12, higher than the four experiments with a wave period of 1.90 seconds on an initial slope of 0.10. The effect of the different reflecting processes does not appear to correlate with any change in wave period (or wavelength). The effect of the steepness of submerged slopes may have been important in all of the experiments, but the correlation between Kp and the offshore slope was much better in the 6-foot tank (Fig. 10). A predominant cause of the variability in experiments 71Y-06. (1.90-second wave), 72D-06 (1.90-second wave; 0.05 initial slope), and 72A-06 (3.75-second wave) was the effect of the elevation at the top of the submerged slope. In all experiments except 72A-10, the foreshore remained fairly stable in shape and the Kp from the foreshore appeared to have been fairly constant, but in 72A-10 the changing foreshore was the predominant cause of Kp variability. The effect of reflection from a plunging breaker appeared to be small and difficult to measure. The increasing width of the inshore shelf (increasing distance between foreshore and offshore) appears to have been a cause of long-term Kp variability in the experiments with the 1.90-second wave and the predominant cause of K, variability in the experiments with the 1.50-second wave (Fig. 11). In the other experi- Ments the distance between the foreshore and offshore changed relatively little and Kp variability was shown to be related to other sources. 3. Variations in Incident Wave Height. In the 10 experiments, the measured incident wave (Table 13) was com- posed of the nominal (generated) wave, the re-reflected wave, and, in experiment 72B-10, the transverse wave. Secondary and cross waves were also observed, but they did not affect the measurement of the incident wave height. Barnard and Pritchard (1972) state that ''Cross waves are standing waves whose crests are at right angles to a wavemaker; they oscillate 44 -quewtzedxe yore ut ssoudseys odors ezoyszzo pue “y 8U07Z 6u1420}j;04 210434540 a4} JO adojS sro v'O0 6 6f1006 «6210 wo 6oVro o¢c0 a aI stoe = J ovo, c-J @ e = sv0a ‘i oe Ol-v2. = oso 0U0Z 6uly20};j;0y 940484; OY) JO Bd01S zo 2420 220 L410 20 200 silo a Ss oz0e e 5 3 e e e e sz 0, e °o O = e e = : ors e A —] 90-VeLl |! ie sto Gu07Z Buyj201j0y 01043550 OY) JO adO)S ofO0 S20 020 GIO o1ro soo soo c J = 2 40108 84Ul0d 2 # e = 3 95 gio ° e e = 0209 e Cy = O1-822 4 F 9u0Z buij20;;ay O40yS5j0 OY) Jo ado\S 210 «6110 «O10 600 800 0 210 110 Oro 60:0 a =) soos = —] O10, o = S\ulod¢ a = si0a . 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Normally, cross waves occur at the generator and result from critical combinations of generated wave- length and tank width. In movable-bed tests with gradual bottom slopes, cross waves have been observed by the author at isolated sections over the profile where the wavelength, as it decreased in shoaling, passed through a critical value with respect to the tank width and remained at that value for sufficient distance to generate a cross wave. Cross waves are a spatial variation in the lateral direction. Cross waves were observed over a short segment of the movable-bed profile in experiment 72B-06; however, the waves lasted only a brief period of time and were not measured. Secondary waves (or solitons) result from the breakdown of a finite- amplitude wave of nonpermanent form into a primary and one or more secondary waves traveling at different speeds dependent on depth. Secondary waves can be generated by a sinusoidally moving generator blade or by a wave as it passes a slope onto a shelf of smaller but constant depth (see Madsen and Mei, 1969 and Galvin, 1972) and are a spatial variation in the longitudinal direction. Secondary waves caused by waves passing onto a shelf probably occurred, but were not recorded. Secondary waves caused by sinusoidal generator blade motion occurred, but (as pointed out in Volume VI for the experiments where secondary waves were most pronounced) the wave height variation due to secondary waves was at least an order-of-magnitude less than the variation due to wave reflection from the profile. Because the incident wave height Measurement was an average of wave heights all along the tanks, the measured incident wave height was not affected by any spatial variation in height due to secondary waves. Transverse waves, generated by a gap at the side of the blade and a critical combination of wavelength and tank width, have an amplitude that varies across the tank, but since the transverse wave has the same period as the plane progressive wave, the combined wave motion causes the wave height at one point to increase from right to left and at another point, farther down the tank, to increase from left to right. (See Madsen, 1974.) Transverse waves are spatial variations in both the lateral and longitudinal directions. Transverse waves were observed and recorded in only experiment 72B-10; a complete discussion of the wave height variability resulting from transverse waves is given in Volume VII. Re-reflection was the primary source of incident wave height varia- bility in these experiments. The effect of re-reflection on incident wave height variability in an experiment can be determined by comparing the difference in the range of wave heights between the fixed- and movable- bed tanks. The wave height variation in the fixed-bed tank is a measure of the wave height measurement accuracy in the movable-bed tank, and sub- tracting the measurement accuracy from the total variation in the movable- bed tank gives a measure of the incident wave height variation due to re-reflection in the movable-bed tank. a. 1.50-Second Wave. The nominal (generated) wave height for the 1.50-second wave period was 0.41 foot (12.5 centimeters). In the 48 fixed-bed tank the average incident wave height was 0.44 foot (13.4 centimeters), 0.03 foot (0.9 centimeter) above the nominal (generated) height, and the range of heights was only 0.03 foot. In the movable-bed tank the range of values was 0.09 foot (2.7 centi- meters), so that 0.06 foot (1.8 centimeters) is assumed due to varying profile reflectivity. The average incident wave height was 0.43 foot (13.1 centimeters), just over the nominal (generated) height by 0.02 foot (0.6 centimeter). b. 1.90-Second Wave. The nominal (generated) wave height for the 1.90-second wave period was 0.36 foot (11.0 centimeters). In the fixed- bed tanks the average incident wave heights for the five 1.90-second tests were all within 0.02 foot of the nominal (generated) height. In the 10- foot tank, initial test length of 61.7 feet (18.8 meters), the average was 0.36 foot, the same as the nominal (generated) height; in the 6-foot tank, initial test length of 100 feet (30.5 meters), the average was 0.37 or 0.38 foot (11.3 or 11.6 centimeters). In four of the five experiments the range of variation in incident wave height was 0.03 foot and in experiment 71Y-06 the range was 0.04 foot (1.2 centimeters). In the movable-bed tank in experiment 70X-06 the range of values was 0.06 foot, 0.03 foot due to varying reflectivity; in experiment 70X-10 the range was 0.05 foot (1.5 centimeters), 0.02 foot due to varying reflectivity; in experiment 71Y-06 the range was 0.07 foot (2.1 centi- meters), 0.03 foot due to varying reflectivity, and in experiment 72D-06 the range was 0.06 foot, 0.03 foot due to varying reflectivity. The average incident wave height in the movable-bed tanks was less than the nominal (generated) height in experiment 70X-06, equal to the nominal (generated) height in experiment 71Y-10, and greater than the nominal (generated) height in experiments 70X-10, 71Y-06, and 72D-06. c. 2.35-Second Wave. The nominal (generated) wave height for the 2.35-second wave period was 0.34 foot (10.4 centimeters). In the fixed- bed tanks the average incident wave height was 0.02 foot above the nominal (generated) height in experiment 72B-06 and equal to the nominal (generated) wave height in experiment 72B-10. The difference was likely due to the difference in initial test length. The range of incident heights was 0.05 foot in experiment 72B-06 and 0.04 foot in experiment 72B-10. In the movable-bed tank in experiment 72B-06 the range of heights was 0.06 foot, only 0.01 foot (0.3 centimeter) due to varying reflec- tivity, and in experiment 72B-10 the range was 0.03 foot, which was . within the accuracy of the wave height measurement; thus, the effect of re-reflection in each experiment was not measurable. d. 3.75-Second Wave. The nominal (generated) wave height for the 3.75-second wave period was 0.31 foot (9.4 centimeters). In the fixed- bed tanks the average incident wave heights were within 0.01 foot of one another and both were greater than the nominal (generated) height. The range of incident height variation was 0.07 foot in experiment 72A-06 and 0.04 foot in experiment 72A-10. 49 In the movable-bed tank in experiment 72A-06 the range of values was 0.10 foot (3.0 centimeters), 0.03 foot due to varying reflectivity, and in experiment 72-10 the range was 0.12 foot (3.7 centimeters), 0.08 foot (2.4 centimeters) due to varying reflectivity. The average incident heights in the movable-bed tanks were 0.07 foot and 0.04 foot, both greater than the nominal (generated) height. e. Comparison of the Ten Experiments. Varying profile reflectivity caused no measurable change in the incident height in experiment 72B-10 (2.35 seconds), a moderate change (0.01 to 0.03 foot) in experiments 70X-06, 70X-10 (1.90 seconds), 71Y-06, 72D-06, 72A-06, and 72B-06, and a Significant change (0.06 to 0.08 foot) in experiments 71Y-10 (1.90 seconds), 72C-10 (1.50 seconds), and 72A-10 (3.75 seconds). The effect in the 6-foot-wide tank was in the moderate range for all five experi- ments and in the 10-foot-wide tank ranged from no change to 0.08 foot, and the effect was not a function of wave period. It appears then that the wider tank may have amplified this effect. III. EQUILIBRIUM PROFILES 1. Definitions and Importance of Equilibrium Profiles. The term "equilibrium profile" implies a profile whose mean position is fixed in space for the given wave and sediment conditions, with the expectation that the actual profile at any given time will deviate some- what from the mean profile. It has been assumed that equilibrium is a state which can be reached on a model profile with a constant wave action impinging on it for a sufficiently long time. Laboratory studies of longshore transport often depend on having an equilibrium profile to determine the longshore transport rate without having an onshore-offshore transport component (Savage, 1959, 1962; Fairchild, 1970a). Coastal engineering models are frequently based on simulating the equilibrium profile. However, Savage (1962) and Fairchild (1970a) found that equilibrium profiles are not always easily attained. Collins and Chesnutt (1975, 1976) showed that the final unchanging pro- file for the same wave and sediment conditions was not always repeatable and that the initial slope could affect the final profile shape. Swart (1974) found that for a single periodic wave impinging on a profile, 1,500 hours of wave action was required to reach equilibrium for some wave and sediment conditions. However, 1,500 hours is not a practical test duration for most models or experiments. J.W. Kamphuis (Professor of Civil Engineering, Queen's University, Kingston, Ontario, personal communication, 1978) used a series of wave conditions replicating a year's seasonal variations and found that when using a wave in the transition region in place of either the winter or summer waves the profile reached equilibrium much less readily than when using only winter and summer waves. Kamphuis further compared two- dimensional tests with three-dimensional tests, and found that 9 to 11 yearly cycles were required to reach equilibrium with the two-dimensional setup and only 1 to 2 cycles with the three-dimensional setup. 50 The LEBS experiments were planned to be run until the profile devel- oped an equilibrium shape because it was assumed that if the profile reached equilibrium, the primary source of temporal wave height varia- bility, the changing profile reflectivity, would be eliminated or sig- nificantly reduced. The effects of varying initial slope and wave period are discussed below. The effect of tank width on profile development is discussed in Section IV. 7c EEeCts Ore ini ti alg hcorilepoloper. Two experiments were conducted in which the only variable was the initial profile slope--0.10 in experiment 71Y-06 and 0.05 in experiment 72D-06. The steeper initial slope in experiment 71Y-06 (Fig. 12) adjusted slowly to the waves and did not appear to have reached equilibrium along any segment of the profile after 375 hours. The foreshore retreated at a rate of 0.113 foot (3.44 centimeters) per hour between 1 and 15 hours and at a rate of 0.025 foot (0.76 centimeter) per hour thereafter. The flat shelf in the inshore zone and the steeper slope in the offshore zone developed between 200 and 220 hours. The flatter initial slope in experiment 72D-06 (Fig. 13) adjusted more quickly to the wave attack, but also did not appear to have reached equilibrium. The foreshore retreated at a rate of 0.05 foot per hour between 5 and 125 hours, prograded seaward between 125 and 135 hours, and then stabilized for the remainder of the experiment. The inshore zone slowly grew in width and the offshore slope remained mild during the first 100 hours. After 100 hours the flat shelf in the inshore zone and the steeper slope in the offshore zone rapidly developed. Once the foreshore stabilized, the inshore zone began eroding, creating a signifi- cant depression in the profile belaw the forshore zone, while the off- shore zone continued to prograde seaward. The Kp stopped varying during the last 25 hours (Fig. 7), indicating that equilibrium may have been near. Although neither profile reached equilibrium, the profiles developed somewhat different shapes (Fig. 14). The differences in rates and types of profile adjustments verify the conclusions of Collins and Chesnutt (1975, 1976) that the initial profile slope can affect the final profile shape. 3. Effect of Wave Period. Nine experiments were conducted with an initial profile slope of 0.10 and four different wave periods; the experiments are analyzed below to determine the effect of wave steepness on profile equilibrium. The deepwater wave steepness was 0.039 for the 1.50-second wave, 0.021 for the 1.90-second wave, 0.013 for the 2.35-second wave, and 0.004 for the 3.75-second wave. 5| } Foreshore Inshore NOM ee NG oy | / ae ‘ = N (45) 4JdaosajuT MS [DUIIIQ Woy souDIsiG eZ [00 150 L000 250) HOO. BD) 0) Cumulative Time (hr) 50 3 x . : 0 nge of experiment 71Y-06. Distance from Original SWL Intercept (ft) = Aw 9 9 tt 15 Inshore 1.0 |G Offshore Se oe Se 40h aE ES 118 a -2.0ft 45 50 @) 5OmanlO Ow SO a 20 0250 Cumulative Time (hr ) Figure 13. Contour movements along center range of experiment 72D-06. ‘sodo[TS [@I}IUT JUILOFFIP PUL DAEM PUODDS-0G"[T & YIIM SaTTjord TeutzZ Fo uostaedwoy (45) }dads9jUT TMS JOUIb14Q wos} adUD\SIG 9G 8b Ov Ge v¢ 9| 8 @) 8- 2|!JO1q 10141] 99-22 ——:— a[tJOld |DIyIU) 9O—A} 2 — - — (14 081 18440) 90-Gzz ------ (4U GJE 42440) 990-A1Z ——— a[1jOld yooeg ‘pl oan3sty (13) IMS 9A0QD: UON}DAa/Z 54 a. 1.50-Second Wave. The profile in the one experiment (72C-10) conducted with a wave period of 1.50 seconds appeared to be near equi- librium, as indicated by horizontal contours in the foreshore zone and most of the inshore zone in Figure 15. Erosion of the foreshore was con- tinuing but slowing along the range 1 side of the tank and some erosion was occurring in parts of the inshore zone. Deposition continued in the offshore zone, but at a slower rate. The breaker type and position had stabilized and the Kp and its variability had decreased to small values. If this experiment had been continued, presumably it would have soon reached equilibrium. The final profile is shown in Figure 16. b. 1.90-Second Wave. Four experiments were conducted with a wave period of 1.90 seconds and an initial slope of 0.10. (1) Experiments 70X-06 and 70X-10. These experiments had a 7-foot longer initial test length than the other experiments in their respective tanks. Because the shoreline was stabilized by the renourish- ment of the backshore after 54 and 62 hours in experiments 70X-06 and 70X-10, the final profile shapes for those experiments may not have been characteristic of profiles for the 1.90-second wave. The final profiles could not have been at equilibrium because sand was still being eroded from the backshore when the experiments were stopped (see Table 10 in Vol. II). However, the nearly horizontal contour lines near the end of the experiment in the offshore in Figure 17 indicate that parts of the profile in experiment 70X-06 may have been approaching equilibrium. It is difficult to determine from Figure 18 if the profile in experiment 70X-10 was approaching equilibrium. Several of the offshore contours had stopped moving in the seaward direction and had begun to move in the shoreward direction, indicating the possible approach to some dynamic equilibrium, but the lateral variations in the shape and development of the profiles (see Vol. II and Section IV,5 in this volume) made it diffi- cult to determine equilibrium. Figure 19 compares the center profiles from the two experiments at 50, 100, and 175 hours, indicating that the profiles at 50 and 100 hours were nearly the same, but that at 175 hours the profile in experiment 70X-10 had built farther seaward while maintaining a similar shape. The profile development after 175 hours in experiment 70X-10 is shown in Figure 20. (2) Experiments 71Y-06 and 71Y-10. These experiments had a shorter initial test length than the two experiments discussed above. There is no indication that either experiment 71Y-06 or 71Y-10 was near equilibrium at the end of the experiments, as shown in Figures 12 and 21; both experiments showed slow, steady development throughout. Figure 22 compares the center profiles from the two experiments at 100, 200, and 300 hours, indicating that at 100 hours the profiles had nearly the same shape; at 200 hours the profile in experiment 71Y-10 had already developed a flat inshore shelf while the profile in experiment 71Y-6 had not, and at 300 hours the profile in experiment 71Y-06 had 55 Distance from Original SWL Intercept (ft) || ft } Foreshore Inshore Offshore -30 0) 50 100 150 200 250 Cumulative Time (hr ) Figure 15. Contour movements along center range of experiment 72C-10. Elevation above SWL (ft) Beach Profile — -— - — 72C-10 Initial Profile 72C-10 (after 140 hr) -8 0 8 16 24 32 Distance from Original SWL Intercept (ft) Figure 16. Equilibrium profile in experiment 72C-10, with steep ''winter"' wave. 57 Distance from Original SWL Intercept (ft) 7 Foreshore Inshore Offshore 25) 30 0) 50 100 150 200 290 Cumulative Time (hr) Figure 17. Contour movements along center range of experiment 70X-06. 58 Distance from Original SWL Intercept (ft) 20 29 30 50 Figure 18. PSs a —& fi\N} (est ee nL 100 150 200 Cumulative Time (hr ) Contour movements along center range of experiment 70X-10. COMR NM O 290 Foreshore Inshore Offshore Figure 0. Beach Profiles after 50 hr Elevation above SWL (ft) -14 -7 (0) Uv 14 2! 28 Distonce from Original SWL Intercept (ft) b. Beach Profiles after 100 hr Elevation above SWL (ft) fe) © ' n -14 -7 ie) 7 14 2l 28 Distance from Original SWL Intercept (ft) c. Beach Profiles ofter 175 hr Elevation obove SWL (ft) ° n ' ~ -4 “14 -7 0 7 14 2l 28 Distance from Originol SWL Intercept (ft) 19. Greater seaward development of profile in experiment 70X-10 than in experiment 70X-06. 60 Elevation above SWL (ft) oi Beach Profile —-— Initial Profile After | 75 hr Seen = After 210 hr 0 T 14 2| 28 Distance from Original SWL Intercept (ft) Figure 20. Profile changes in experiment 70X-10 during the last 35 hours. 6 35 Olt NIE a } Foreshore GL J 0.2 0.4 0.6 Inshore Distance from Original SWL Intercept ( ft) Offshore 3 l 2 0 50 100 0) 400) 250) sss Ss) I) Cumulative Time (hr ) Figure 21. Contour movements along center range of experiment 71Y-10. Elevation above SWL (ft) Elevation above SWL (ft) Elevation above SWL (ft) a. Beach Profiles after 100 hr 2 {o} -2 -4 -14 7 (0) 7 14 2 28 Distance from Original SWL Intercept (ft) 4 b. Beach Profiles after 200 hr -14 -7 0 7 14 2l 28 Distance from Original SWL Intercept (ft) c. Beach Profiles ofter 300 hr -14 -7 {¢) 7 14 2l 268 Distonce from Original SWL Intercept (ft) Figure 22. Greater seaward development of the profile in experiment 71Y-06 than in 71Y-10. 63 developed the flat inshore shelf and had surpassed experiment 71Y-10 in the progradation of the offshore zone. The comparison of the final pro- files for the two experiments in Figure 23 indicates that the experiments had roughly the same shape, but that in experiment 71Y-06 the foreshore had eroded farther landward and the offshore had prograded farther sea- ward. (3) Comparison of the Four Experiments. The final profiles in the experiments with the 1.90-second waves are compared in Figure 24, showing that the profile shape was similar in all four experiments, but that the longer the experiment, the farther landward the foreshore and the farther seaward the offshore. The Kp variability increased with time during each test (Figs. 3 to 6). This indicates that if an equi- librium slope can be attained for the 1.90-second period on an initial 0.10 sand slope, it is probably shaped like these four profiles with an even longer inshore zone. c. 2.35-Second Wave. The profile in experiment 72B-06 adjusted slowly to the waves and appeared to be near equilibrium at the end of the experiment (150 hours) (Fig. 25); the profile in experiment 72B-10 adjusted more rapidly and did not appear to be near equilibrium at the end of the experiment (150 hours) (Fig. 26). The differences in rate of profile adjustment and the differences in the shape of the offshore zone between the two experiments are shown in Figure 27. These differences may have been caused by differences in tank width and initial test length or by the transverse wave which was only generated in experiment 72B-10. d. 3.75-Second Wave. Two experiments were conducted with a 3.75- second wave. Although the profile in the narrower tank (experiment 72A-06) did not appear close to equilibrium, the profile in the wider tank (experiment 72A-10) did, as shown by comparing Figures 28 and 29. The development and disintegration of circulation cells between antinodes of the standing wave envelope evidently prevented the profile from reach- ing equilibrium in experiment 72A-06 (discussed in Vol. VI). The absence of any horizontal contours in Figure 28 (narrower tank) shows this lack of equilibrium. However, in the wider tank, nearly all contours are horizontal after only 25 hours (Fig. 29). Figure 30 compares the center profiles from the two experiments at 25, 50, and 80 hours, indicating that throughout the experiments the profile shapes were quite different in the two tanks, probably as a result of the circulation pattern in experiment 72A-06. Profile changes during the final 55 hours of experiment 72A-06 are shown in Figure 31. The offshore zone changed to a more gently sloping region. e. Comparison of the Profiles. Although the profile in experiment 71Y-06 was not at equilibrium, it appears to well represent the shape of profile adjustment for a 1.90-second wave. The profile in experiment 72C-10 (1.50-second wave) was close to equilibrium and is assumed to be 64 Elevation above SWL (ft) Elevation above SWL (ft) -/ Figure 23. af Figure 24. _ Beach Profile _ — 7IY-06 (after 375 hr) Ee 7IY- 10 (after 335 hr) —v-— 71Y Initial Profile 0 a 14 2l 28 Distance from Original SWL Intercept (ft) Final profiles in experiments 71Y-06 and 71Y-10 with the longest test durations in the series. Beach Profile 70X-06 (after 175 hr) —-—— 70X-1[0 (after 210hr) SUE al 71Y-06 (after 375hr) noone 71Y-10 (after 335 hr) —-— Initial Profile 0) 1 14 2| 28 Distance from Original SWL Intercept (ft) Comparison of final profiles with a wave period of 1.90 seconds and an initial slope of 0.10. 65 35 2 D0) Distance from Original SWL Intercept (ft) i ae 0.6 ft Ni eats 0.4 OR 0.2 Foreshore 0.0 - 0.2 5 i “ae ito aS aE NNR ING --0.8 - 1.0 = 152 0 | asian - 1.4 - 1.6 IS 5 Se Offshore 20 25 -2.0 Tenentt 30 O 50 100 150 200 250 Cumulative Time (hr) Figure 25. Contour movements along center range of experiment 72B-06. 66 Distance from Original SWL Intercept (ft) Foreshore i pe a Inshore 10 Uk -0.8 Oe {1,0 ame ee = Ae NE “18 0 SE ZS = ; AT eae Off yee shore a ee J 16 20 Sn a) a a aS = at |.8 TE Oc ee ay -2.2 ft ZS) 30 0) 50 100 150 200 250 Cumulative Time (hr) Figure 26. Contour movement along center range of experiment 72B-10. 67 0. Beach Profiles ofter 50 hr Elevation above SWL (f1) -16 -8 {¢) 8 16 24 32 Distance from Original SWL Intercept (ft) b. Beach Profiles ofter 100 hr Elevation above SWL (ft) -16 -8 (0) 8 16 24 32 Distance from Original SWL Intercept (ft) c. Beach Profiles ofter 150 hr Elevation above SWL (ft) -16 -8 {e) 8 16 24 32 Distance from Original SWL Intercept (ft) Figure 27. Development of different offshore shapes: concave upward in experiment 72B-06 and convex upward in experiment 72B-10. 68 =02 : LL 0,2 (¢ Momsen Distance from Original SWL Intercept ( ft ) ) é 2B Offshore 6) ZS -2.2 ft 30 39 0 50 100 150 200 290 Cumulative Time (hr ) Figure 28. Contour movements along center range of experiment 72A-06. 69 Distance from Original SWL Intercept (ft) RORit RI NS 08 Ree 0G Sea «04 SSeS 6 —— oe Foreshore SVE 20.2 INS 33 IRAE -0.6 5 [ \ = 10 lOF Ve ine Offshore ia ag ee i Ri te ee tO eee SSS keer onal i = 1.8 20, VAR |—__—_—___~-—_- - 2.2 ft 29 30 0) 50 100 150 200 250 Cumulative Time (hr ) Figure 29. Contour movements along center range of experiment 72A-10. 70 0. Beach Profiles ofter 25 hr Elevation above SWL (ft) ° ‘ Nn -4 -16 -8 (0) 8 16 24 32 Distance from Original SWL Intercept (ft) 4 b. Beoch Profiles after 50 hr 2 ——_ 724-06 sacesso 72A-10 os 72A Initial Profile Elevation above SWL (ft) -16 -8 (0) 8 16 24 32 Distonce from Original SWL Intercept (ft) 4 c. Beach Profiles after 80 hr 2 —— 72A-06 72A-10 a 72A Initial Profile Elevation above SWL (ft) -16 -8 0 & 16 24 32 Distance from Original SWL Intercept (ft) Figure 30. Development of a higher foreshore in experiment 72A-10 and a steeper off- shore in experiment 72A-06. 7 Beach Frofile —— - —— Initial Profile Fl eewn N After 80 hr After 135 hr Elevation above SWL (ft) 4 -16 -8 O 8 16 24 Se Distance from Original SWL Intercept (ft) Figure 31. Profile change in experiment 72A-06 during the last 55 hours. 72 representative of a profile adjustment for a 1.50-second wave. The pro- files in experiments 72A-10 and 72B-06 were close to or at equilibrium and are assumed to typify profile adjustment for 3.75- and 2.35-second waves. These four profiles are compared in Figure 32. The profile from experiment 72A-10 (Hj/Lo = 0.004 at 80 hours) is typical of the step-type or summer (prograding shoreline) profile, with a high berm and a step at the toe of the foreshore zone. The profile from experiment 72B-06 (H,/Lo = 0.013 at 150 hours) is also somewhat typical of the summer profile, except that the berm crest is lower and the lower foreshore appears to be half-bar and half-step. On both of these two profiles, some deposition occurred in the offshore zone, more in the H,/Lo = 0.013 experiment than in the H o/Lo = 0.004 experiment. The profile from experiment 71Y-06 (Ho/Lo = 0. 021 at 375 hours) is cer- tainly an eroding profile consisting Of Beco foreshore and offshore zones separated by a long shelf with several shallow bars and troughs. The pro- file from experiment 72C-10 (Hj/L5 = 0.039 at 140 hours) is typical of the bar-type or winter (rodane Bhoreltine) profile with a vertical scarp, a steep foreshore, a longshore bar, and offshore deposition. The transition zone between the two types of profiles is normally accepted to be between H,/L, = 0.020 and 0.025 and the profiles from the five experiments with H,/L, = 0.021 could certainly not be classified as either winter or summer. In fact, this was the least stable of the four conditions, with none of the five profiles close to equilibrium. With the other three wave steepnesses, at least one of the profiles appeared to be near a stable shape. This agrees with the findings of Kamphuis (personal communication, 1978) that waves in the transition region tend to take longer to develop an equilibrium profile. The final profiles from experiments 72C-10, 71Y-10, 72B-10, and 72A-10 were averaged to develop a standard initial profile (Fig. 33) to be used in longshore transport experiments in CERC's Shore Processes Test Basin (SPTB) (P. Vitale, hydraulic engineer, CERC, personal communi- cation, 1976). This standard profile will also be used in a study of wier jetties in the SPTB (J.R. Weggel, Chief, Evaluation Branch, CERC, personal communication, 1977). f. Discussion of Results. The four experiments with the 1.90-second wave verify the findings of Savage (1962) and Fairchild (1970a) that an equilibrium profile is not always easily attained, even with the wave direction normal to the shoreline. The four experiments with the 3.75- and 2.35-second waves verify the findings of Collins and Chesnutt (1975, 1976) that profiles for the same wave conditions do not always have the same shape. In particular, the experiments with 3.75- and 2.35-second waves point out that the physical constraints of the laboratory facilities can affect the final profile shape. The currents in experiment 72A-06 (3.75 seconds) and the transverse wave in experiment 72B-10 (2.35 seconds) kept those from reaching equilibrium. In judging the evidence presented here, profile equilibrium in basi- cally two-dimensional tests does not appear to be an easily definable, US Elevation above SWL (ft) Figure 32. 4 Elevation above SWL (ft) (@) ine) ' ine) Falourens Sy. Experiments Ho/Lo —-— Initial 0.1 Slope . ----- 72A-10 (after 8Ohr) 0.004 —--— 72B-06 (after |50hr) 0.013 —— 7lY-06 (after 375 hr) 0.021 es —-— 72C-10 (after 140hr) 0.039 -8 6) 8 16 24 32 40 Distance from Original SWL Intercept (ft) Comparison of the equilibrium or representative profile for each wave steepness. -8 0 8 16 24 32 40 Distance from Original SWL. Intercept (ft) Preliminary beach profile of Vitale (personal communication, 1976), developed from the final profiles of experiments 72C-10, 71Y-10, 72B-10, and 72A-10. 74 attainable, or a useful state to be trying to reach in experiments of practical duration. Coastal engineering might be better advanced if researchers were more concerned with trying to reach some constant rate of profile change or a rate of profile change small in comparison to other variables. IV. LABORATORY EFFECTS 1. Definitions of Terms. Laboratory effects are the undesired differences between laboratory and prototype conditions caused by the physical constraints which exist in the laboratory, but not in the field. For example, the variations in incident wave height discussed in Section II, 3 are laboratory effects; i.e., the mechanical generator at one end of the wave tank caused a re- reflection of the wave energy propagating away from the profile that would not have occurred in nature. This project evolved from an investi- gation of wave height variability and equilibrium profiles into a more comprehensive examination of all laboratory effects. This section analyzes five laboratory effects based on results from the 10 experiments. Other known laboratory effects are also identified. 2. Test Length and Initial Slope Effects. a. Processes. Two physical processes are known to be affected by changes in initial test length: re-reflection of waves from the wave generator and secondary waves. (1) Re-Reflection. The height of the incident wave is a func- tion of the height of the nominal (generated) and re-reflected waves and the phase difference between the re-reflected wave and the wave generator motion. The height and phase of the re-reflected wave are functions of the height and phase of the reflected wave. The height of the reflected wave is a function of the profile reflectivity. The phase of the reflec- ted wave with respect to the generator motion is a function of the dis- tance between the profile and the generator. The effect of initial test length on re-reflection and incident wave height variability is discussed in Section II, 3. The effect of incident wave height variability on the profile is discussed in this section. (2) Secondary Waves. Secondary waves cause a spatial (longi- tudinal) variation in wave height and a variation in the asymmetry of the velocity distribution under a wave. The degree of asymmetry obviously depends on the position along the tank. In this case the distance to the toe of the initial profile from the generator is the controlling distance. b. Initial Test Length Effect. Four pairs of experiments are ex- amined here. In two pairs (experiments 70X-06 and 71Y-06 and experiments UD 70X-10 and 71Y-10) the initial test length was the only variable; in the other two pairs (experiments 72B-06 and 72B-10 and experiments 72A-06 and 72A-10) both initial test length and tank width varied, but the effects of initial test length are distinguishable from the tank width effects. (1) Experiments 70X-06 and 71Y-06 (1.90-Second Wave). In each experiment the effect of re-reflection on the incident wave height was the same, 0.03 foot (Table 13). However, the average incident wave height was 0.34 foot in experiment 70X-06 and 0.37 foot in experiment 71Y-06, and the difference in incident height is likely due to the dif- ference in the phase difference as a result of the 7-foot difference in initial test length. The profiles in the two experiments developed similar shapes (Fig. 24), with the length of the inshore shelf the only difference, due pri- marily to the 200-hour difference in the duration of the experiments. However, the rate of shoreline recession was quite different (Fig. 34). In experiment 70X-06 the shoreline recession rate was 0.06 foot per hour between 1 and 22 hours, 0.14 foot (4.2 centimeters) per hour between 22 and 30 hours, 0.10 foot per hour between 30 and 44 hours, and 0 there- after. The backshore was artificially nourished after 54 hours, thus maintaining the stable shoreline after that time. In experiment 71Y-06 the rate was 0.113 foot per hour between 1 and 15 hours and 0.025 foot per hour thereafter (for 360 hours). The differences in profile adjustment rates may have been caused by the difference in initial test length; if so, the difference was not due to re-reflection effects, since the higher recession rate was associated with the lower incident wave height. It is unlikely that secondary waves would have caused the difference in shoreline recession rates without also affecting the profile shape and such profile shape differences were not observed. (2) Experiments 70X-10 and 71Y-10 (1.90-Second Wave). In each of these experiments the effect of re-reflection on the incident wave height was different, 0.02 foot in experiment 70X-10 and 0.06 foot in experiment 71Y-10 (Table 13). However, the average incident wave height was almost the same, 0.37 foot in experiment 70X-10 and 0.36 foot in experiment 71Y-10, even though the initial test length had a difference of 7 feet in the two experiments. The profiles in the two experiments developed similar shapes (Fig. 24), with the length of the inshore shelf the only difference, due pri- marily to the 125-hour difference in the duration of the experiments. However, the rate of shoreline recession was quite different (Fig. 34). In experiment 70X-10 the shoreline recession rate was 0.08 foot per hour between 12 and 62 hours, and 0 thereafter because the backshore was re- nourished to maintain a stable shoreline position. In experiment 71Y-10 the rate was 0.133 foot (4.05 centimeters) per hour (uniform laterally) between 1 and 15 hours, 0.016 foot per hour (uniform laterally) between 76 Distance from Original SWL Intercept (ft) 0 Figure 34. 50 100 150 200 250 300 350 400 Cumulative Time (hr) Comparison of shoreline movement in four experiments with a 1.90-second wave and a 0.10 initial slope. Cana 15 and 205 hours, and varied from 0.016 foot per hour along the center of the tank to 0.025 foot per hour along the tank walls thereafter (for 130 hours). Re-reflection is not the likely explanation for the difference in shoreline recession rates, since there was little difference in average incident wave heights and the slower recession rate was associated with the higher range of re-reflection effect within an experiment. Secondary waves are not a likely cause because there was no difference in profile shape. (3) Experiments 72B-06 and 72B-10 (2.35-Second Wave). In these two experiments the effect of re-reflection on the incident wave height variability was slight. In experiment 72B-06 the range of incident wave heights in the movable-bed tank was only 0.01 foot greater than in the fixed-bed tank; in experiment 72B-10 the range in the movable-bed tank was less than in the fixed-bed tank (Table 13). However, there was a 0.07-foot difference in average incident wave height. The average Kp was lower in experiment 72B-06 than in experiment 72B-10, indicating that Hp and Hpp would have been lower in experiment 72B-06. The higher Hy in experiment 72B-06 must then have been the result of the difference in phase difference between H; and Hpp as a result of the 38.3-foot (11.7 meters) difference in initial test length. Secondary waves were also present. The profiles in the two experiments developed different profile shapes. Some of those differences were due to the differences in tank width and the presence of the transverse wave in experiment 72B-10 (discussed in the following subsection). In experiment 72B-06 the off- shore zone had a concave-upward shape; in experiment 72B-10 the offshore zone had a convex-upward shape (Fig. 27,c). This significant difference could have been caused by either secondary waves or re-reflection effects, as a result of the difference in initial test length. This difference in offshore profile shape may have been a contributing cause to the lack of equilibrium in experiment 72B-10. (4) Experiments 72A-06 and 72A-10. In each of these experiments the effect of re-reflection on the incident wave height variability was different, 0.03 foot in experiment 72A-06 and 0.08 foot in experiment 72A-10; the difference in average incident wave height between the two experiments (0.03 foot) was significant (Table 13). Thus, varying re- flectivity within an experiment caused variations in H;; and the 38.3- foot difference in initial test length affected the average Hy. Secondary waves were the most pronounced in these experiments. The profiles in the two experiments developed different shapes (Fig. 31). Some of the \differences were due to tank width effects, which are discussed in the following subsection. The differences in the shape of the outer offshore were probably due to re-reflection or secondary wave effects. In experiment 72A-06 the outer offshore had a steep segment between stations 16 and 20 and a bar at station 28. In experiment 72A-10 78 the outer offshore below -1.9 feet remained unchanged throughout the experiment. The differences in foreshore berm-crest elevation may have resulted from the differences in the outer offshore, but these cannot be determined. c. Initial Slope Effect. The effect of varying the initial slope can be seen by comparing experiment 71Y-06 with an initial slope of 0.10 and experiment 72D-06 with an initial slope of 0.05. All other parameters were equal in these two experiments. In each of these experiments the effect of re-reflection on the inci- dent wave height variability was the same (0.03 foot), but there was a 0.02-foot difference in average incident wave height (Table 13). Re- reflection caused a higher average incident wave height in the experi- ment with the flatter initial slope. The distance from the generator to the toe of the initial slope was 23 feet greater in experiment 71Y-06 (0.10 slope); thus, the velocity distribution at the toe of the slope may have been different in the two experiments. The offshore profiles in these two experiments developed similar shapes (Fig. 14), but the inshore zone developed somewhat differently. In experiment 72D-06 (0.05 initial slope) the flat shelf in the inshore zone developed during the first 100 hours and a trough was scoured in the zone after the foreshore stabilized at 135 hours. In experiment 71Y-06 (0.10 initial slope) the flat shelf in the inshore zone developed between 200 and 220 hours and then continued to widen as the foreshore and offshore separated. It is not possible to ascertain whether re-reflection, secondary waves, or some other phenomena caused the profiles to develop such different inshores, but it was probably the result of the difference in initial slope. 3. Tank Width Effects. When the wavelength, L, is much larger than the tank width, W, then the wave tank is 'narrow'' and the result of wave action on the sand bed is expected to be two dimensional; i.e., without lateral variations in profile shape. When L is much smaller than W, then the wave tank is essentially a "basin" and the result of wave action on the sand bed, even when wave direction is normal to the initial shoreline, is expected to be three dimensional; i.e., with lateral variations in profile shape. In the intermediate case, when the tank width and wavelength are nearly the same (L/W = 1), the wave tank is wide enough for the lateral varia- tions to begin to occur, but the tank walls confine the third dimension of current patterns and sediment movement to an unknown extent. In the 10 LEBS experiments, L had values that ranged from equal to W to several times larger than W, so the point at which a wave tank becomes Narrow can be examined. (69 The confining effect of the tank walls on flow in the longshore di- rection is complicated by other tank width effects. There are critical wavelengths for each tank width which can generate tank oscillations or unique circulation patterns (see Sec. II). Cross waves were observed over a limited segment of the profile for a short period of time in ex- periment 72B-06 (Vol. VII), but neither the cross waves nor their effect on the profile were measured. Transverse waves were observed and meas- ured throughout experiment 72B-10 (Vol. VII) and their effect on the profile determined. Circulation currents between the antinodes of the standing wave, along with their effects, were measured in experiment 72A-06 (Vol. VI). These three special cases of tank width effects are assumed to produce special effects on the sand beds. Tank width effects in all 10 experiments from lowest to highest wave period tested are discussed below. a. 1.50-Second Wave (L/W = 1.03, Experiment 72C-10). The foreshore and inshore zones had significant lateral variations. The shoreline sta- tion along the five ranges varied as much as 2.5 feet (0.76 meter) at any given time (Fig. 35). Specific instances of this variation are illustra- ted by the two photos in Figure 36. At 50 hours (Fig. 36,a) the shore- line and scarp on the near side (ranges 1 and 3) are farther landward than the shoreline along the far side (ranges 7 and 9). At this time the backshore, was apparently eroding along ranges 1 and 3, and the sand moved alongshore to range 7 where it caused the shoreline to protrude into the inshore zone. At 85 hours (Fig. 36,b) the scarp was uniform in position across the tank, but the position of the shoreline was seaward- most on the near side (range 1) and landwardmost in the middle (range 5). At this time the backshore was apparently eroding in the middle of the tank, and the sand moved alongshore to range 1 where it moved out into the inshore zone. At other times the erosion of the backshore occurred only along ranges 7 and 9 and the sand was transported alongshore to range 1 before moving into the inshore. Considerable lateral variation also occurred in the inshore zone of this experiment (Fig. 37 compares movements of the -0.3-, -0.4-, -0.5-, -0.7-, and -0.8-foot (-9.1, -12.2, -15.2, -21.3, and -24.4 centimeters) contours). The lateral variations were particularly great just below the foreshore (elevation -0.3 foot) and the amount of variation decreased moving in the seaward direction. No lateral variation occurred in the offshore zone (Fig. 38 compares movements of the -0.9-, -1.4-, and -1.9-foot (-27.4, -42.7, and -57.9 centimeters) contours). Erosion of a trough near station 10 started first along the tank walls and pro- ' gressed toward the center (discussed in Vol. V). The three dimensionality of the profile shape is shown in Figure 39, which is a contour map of the sand bed at the end of the experiment. The foreshore and offshore topographies are skewed in the same direction and the inshore topography is approximately symmetric about the tank centerlines. The symmetric development of the inshore is illustrated by the depressions along the tank walls near stations 3 and 13. The tank walls obviously constrained the shape that did develop, but that shape does have a significant variation in the third (longshore) dimension. 80 Distance from Original SWL Intercept (ft) 0 50 100 150 200 Cumulative Time (hr) Figure 35. Shoreline movement of five ranges in experiment 72C-10 (L/W = 1.03). 8| a : oo a a S ae i b. At 8S hr Figure 36. Foreshore variability over 35-hour period in experiment 72C-10 (L/W = 1.03). 82 -0.5-ft Contour 0.0 Distance from Original SWL Intercept (ft) -0.8-ft Contour 150 100 Cumulative Time (hr) Figure 37. Lateral variations in movement of inshore zone contours in experiment 72C-10 (L/W = 1.03). 83 5.0 -0.9-ff Contour 20.0 -|.4-ff Contour Distance from Original SWL Intercept (ft) oO: 50 100 150 Cumulative Time (hr) Figure 38. Lack of lateral variations in movement of offshore zone contours in experiment 72C-10 (L/W = 1.03). 84 Seawardmost position of each contour Other more landward positions of a given contour SSS => Distance from Original SWL Intercept (ft) Figure 39. Profile shape at end (140 hours) of experiment 72C-10 (L/W = 1.03). 85 b. 1.90-Second Wave. (1) L/W = 1.43 (Experiments 70X-10 and 71Y-10). Although the foreshore had some lateral variations, the inshore zones had greater lateral variations, particularly in the development of the flat shelf in the inshore in experiments 70X-10 and 71Y-10, the experiments with the next highest value of L/W. In both experiments with L/W = 1.43, the slope of the foreshore and position of the shoreline varied with range at any one time and with time at any one range. The slope varied from 0.04 to 0.60 in experiment 70X-10 and from 0.08 to 0.56 in experiment 71Y-10. The shoreline position at any one time varied up to 1.6 feet (48.8 centimeters) in experiment 70X-10 and 2.0 feet in experiment 71Y-10 (Fig. 40) (compared to up to 2.5 feet with L/W = 1.03). The most important profile change in all of the experiments with the 1.90-second wave was the development of the long flat shelf with- in the inshore zone. In experiment 70X-10 the shelf development began at 15 hours along range 1 and at 95 hours along range 9, as indicated by the initial upward movements of the -0.6-foot contour positions in Figure 41. In experiment 71Y-10 (Fig. 41) the shelf development began at 210 hours along range 1 and 110 hours along range 9. The 80-hour difference in experiment 70X-10 and the 100-hour difference in experiment 71Y-10 are significant--that this variation occurred in both experiments in the same tank and that the development started on one side in one experiment and on the other side in the other experiment indicates that the varia- tion was not due to a unique external influence or some misalinement in the tank. The three dimensionality of the profile shape at the end of the ex- periments is shown in Figure 42. The offshore zones are skewed seaward along ranges 7 and 9 in both experiments, just as in experiment 72C-10. (2) L/W = 2.38 (Experiments 70X-06, 71Y-06, and 72D-06). In three experiments with a 1.90-second wave conducted in the narrower tank, the profile shape usually had less lateral variation, as would be expected from the higher value of L/W. In these experiments, lateral variations in slope and position oc- curred on the foreshore. The foreshore slope varied from 0.10 to 0.36 in experiment 70X-06, from 0.08 to 0.52 in experiment 71Y-06, and from 0.02 to 0.50 in experiment 72D-06 (the experiment with a 0.05 initial slope). The shoreline position varied as much as 2.0 feet in experiment 70X-06, 2.3 feet (70.1 centimeters) in experiment 71Y-06, and 1.9 feet in experiment 72D-06 (Fig. 43). The foreshore variations are not less than those with L/W = 1.43 (compare Fig. 43 with Fig. 40), especially since the tank was narrower. The inshore in experiment 70X-06 developed the flat shelf with little lateral variation in time of development, but after the shelf developed lateral variations occurred, as indicated by the -0.6-foot contour move- ments in Figure 44. The same holds for experiment 71Y-06 (Fig. 44). In 86 \ oO Distance from Original SWL Intercept ( ft ) ) Figure 40. 50 100 0.0 Contour 150 200 Cumulative Time (hr) 250 Shoreline movement in experiments (L/W = 1.43). 87 300 350 70X-10 and 71Y-10 -0.6-ft Contour Range mo (o) wo 1S) (44) sdaosajyuT TMS jOUIH14Q wos a2UD}SIQ 10 OM 15 300 350 250 50 Cumulative Time(hr) Comparison of the movements of the -0.6-foot contour in experiments 70X-10 and 71Y-10 (L/W Figure 37. Figure 41. Compare with LAS) 6 88 70x-10 71 Y-10 (after 335 hr) eenfashee ent (after 210 hr) 1 \ =||Ornmy =|| (0) 0.2 ft 0.0 -0.2 -0.4 -0.6 =(0),7/ Distance from Original SWL Intercept (ft) Distance from Original SWL Intercept (ft) Seawardmost position of each contour Other more landward positions of a given contour SRSo => I 1 1 ' 1 ae JS 1D Tighe) I So 08 Figure 42. Profile shape at end of experiments 70X-10 and 71Y-10 (L/W = 1.43). Compare with Figure 39. 89 Distance from Original SWL Intercept (ft) So u fe) ( ao om (0) 50 100 150 200 250 300 350 400 Cumulative Time (hr) Figure 43. Shoreline movement in experiments 70X-06, 71Y-06, and 72D-06 (L/W = 2.38). Compare with Figure 40. 90 —0.6-ft Contour Range 1 3—: — —— Distance from Original SWL Intercept (ft) (0) 50 100 150 200 250 300 350 400 Cumulative Time (hr) Figure 44. Comparison of the -0.6-foot contour movements in experiments 70X-06, 71Y-06, and 72D-06 (L/W = 2.38). Compare with Figure 41. 9I experiment 72D-06 the flat inshore developed quickly and then a large trough was scoured at the shoreward end of the inshore. In contrast to experiments 70X-06 and 71Y-06, the lateral variations in the position of the -0.6-foot contour in experiment 72D-06 (Fig. 44) occurred while the inshore was a flat shelf, perhaps because of the differences in initial slope. Contour maps of the final profile shape for the three experiments are in Figure 45, The profile shape obviously varied laterally, particularly in the foreshore and inshore, but in the offshore zone the variations were less than in the wider tank. c. 2.35-Second Wave. (1) L/W = 1.86 (Experiment 72B-10). In experiment 72B-10, the L/W ratio was less than the three experiments in the 6-foot tank with the shorter 1.90-second wave. The profile in this experiment was affec- ted by the transverse wave, generated by the gap at the end of the gene- rator blade. Thus, the width effects identified here are the result of the "generator gap effect," which is another special case of width effects. The foreshore slope and position varied laterally and with time, as a result of the three-dimensional swash movement. The slope varied from 0.10 to 0.54. During the first 100 hours and between 130 and 150 hours, the shoreline position was skewed across the tank, with up to a 1.2-foot difference in shoreline position between range 1 (seawardmost) and range 9 (landwardmost) (Fig. 46). Between 100 and 130 hours the shoreline position was not skewed. In the inshore a longshore bar developed near station 2 and later eroded, and a flat area developed near station 5 and later developed into a bar. The above changes occurred at different times along each range, as shown by the variation in movement of the different contours in Figure 47, and as discussed in Volume VII. Flat areas developed in the offshore zone near stations 8 and 16, but in each case the elevation of this flat area increased from the range 1 side to the range 9 side. Sand deposited at the toe of the slope along ranges 1 and 3, but not along ranges 5, 7, and 9. The lateral variation of contours in each of the three areas is shown in Figure 48. The final profile shape is shown in Figure 49 with lateral variations in the areas discussed above. (2) L/W = 3.10 (Experiment 72B-06). In experiment 72B-06 the lateral variations in profile shape were minimal. The foreshore slope varied from 0.10 to 0.46 as a result of lateral variations in swash move- ment, but the shoreline position varied as much as 0.5 foot only once and was generally uniform (Fig. 50). Je 70X-06 71 Y-06 72D-06 (after 175 hr) (after 375 hr) (after 180 hr) -20;-, I | -20 -5 Ltt | ort ——— | 00 Seawardmost position a -0.2 of each contour Sie eeess -03 = Other more landward Cee aE Irs) positions of a given 0 fesreeesy |L gig contour SS SR eEe -0.6 ©-0.7 *~---2 -0.8 =| -10 Ss) Se pene ay e nee ~2 ||-).2 Spee SS oS oes Sees - 1.3 oa = STOR. eins o~ SA fe) _— ~S a NS SS = @ ee = 3 oO o L ee) uu — > od @ ® = = [ke c c SSeS hee ME = ae ee a) =I Sem—ale| = — a a 2 aS.) - 1.0 S S ° 55 | 1.0 e c e 207. ic. > el hay Sees (ae S 3 S ~0.9 E E We aca S S Sys 5 Eee = = os if “> |-0.8 @ @ @ va c c = ~~~ S) 2 2 2 2 © 30 a ron) (an) i -0.8 oe = 1.0 aaa —>— ]-1.2 ees OEE ae Se | 4 20; aes |= 16 39 pee CO o—_-——- |- 1.8 —__, Bike —-— |-2.0Ft Ceaeain| i ToS o—-——- |- 1.4 See |G o—-—_ — —~ |-2.0ft C= as I I I I i 4 \ I I Som 3.5 eae esis ale os Range Range Range Figure 45. Profile shape at end of experiments 70X-06, 71Y-06, and 72D-06 (L/W = 2.38). Compare with Figure 42. 93 oO 50 100 150 Cumulative Time (hr) Distance from Original SWL Intercept (ft) Figure 46. Shoreline movement in experiment 72B-10 (L/W = 1.86). Compare with Figure 40. 94 Range -0.5-ft Contour rer Distance from Original SWL Intercept (ft) re) 50 100 150 Cumulative Time (hr) Figure 47. Lateral variations in the movements of inshore zone contours in experiment 72B-10 (L/W = 1.86). Compare with Figure 41. 95 -|.0-ft Contour -|,5-ft Contour Distance from Original SWL Intercept (ft) oO O 50 100 150 Cumulative Time (hr) Figure 48. Lateral variations in the movements of off- shore zone contours in experiment 72B-10 (L/W = 1.86). Compare with Figure 38. 96 Distance from Original SWL Intercept (ft) 25 Seawardmost position of each contour Other more landward positions of a given contour SS Range Figure 49. Profile shape at end (150 hours) of experiment 72B-10 (L/W = 1.86). Compare with Figure 42. Sil Distance from Original SWL Intercept (ft) Figure 50. 50 100 150 Cumulative Time (hr) Shoreline movement in experiment 72B-06 (L/W = 3.10). Compare with Figure 43. 98 In the inshore, little significant lateral variation occurred at elevations -0.4, -0.5, and -0.6 foot; only a random variation in the times at which the longshore bar crest reached elevation -0.3 foot (aig, Sil). Large lateral variations occurred in position of particular contours in the offshore (Fig. 52), indicating that the crest elevation of the seaward bar reached -2.0 feet at different times, but the variations had no pattern. At the end of the experiment the only significant lateral variation was the slope of the foreshore (Fig. 53). d. 3.75-Second Wave. (1) L/W = 3.14 (Experiment 72A-10). Experiment 72A-10 had a longer wavelength in a wider tank than experiment 72B-06 discussed above, with the result that the L/W ratio was nearly the same (3.14 versus 3.10). As expected, this experiment also had little significant lateral variation. The foreshore slope was steeper along the middle ranges (3, 5, and 7), varying from 0.14 to 0.36 with an average of 0.20, and flatter along the outside ranges (1 and 9), varying from 0.12 to 0.30 with an average of 0.18. The shoreline position varied laterally during the first 25 hours as it prograded first along the outside ranges (Fig. 54). Between 30 and 50 hours the shoreline position also varied laterally. At other times the shoreline position was quite uniform. The only lateral variations in the offshore zone were differences in the bar-crest elevation along the different ranges (Fig. 55), but this was a fairly minor variation in elevation. A contour map of the profile at the end of the experiment in Figure 56 shows how little the lateral variations were. (2) L/W = 5.23 (Experiment 72A-06). In experiment 72A-06, with the highest L/W value, the lateral variations in profile shape were quite large, contrary to what was expected. In the foreshore, a strong counterclockwise circulation caused the foreshore slope to be steeper (0.20) along range 5 and flatter (0.12) along range 1, but only at 115 hours was there a large (1.3 feet) lateral difference in shoreline position (Fig. 57). In the inner offshore zone, a clockwise circulation developed between the antinodes in the foreshore and near station 18 during the first 70 hours, and then began disintegrating. The wavelength in this area was approximately 24 feet (7.3 meters), or four times the tank width, which suggests that the circulation was the result of some resonance unique to a laboratory wave tank. This is apparently another special tank width 99 Distance from Original SWL Intercept (ft) —0.3-ft Contour —0.4-ft Contour —— =O." Comrour Cc Figure 51. —0.6-Contour 50 100 150 umulative Time (hr) Comparison of the movements of inshore zone contours in experiment 72B-06 (L/W = 3.10). Compare with Figure 44. 100 Distance from Original SWL Intercept (ff) —2.0-ft Contour r) 50 100 150 Cumulative Time (hn Figure 52. Comparison of the movements of offshore zone contours in experiment 72B-06 (L/W = 3.10). Compare with Figure 48. 101 Distance from Original SWL Intercept ( ft) S) 20 25 30 Figure 53. eo———_.—___ cot henner cece), OJ6itt Ne co || OG Ei eee 0.6 —— 0.4 Ee 0.2 o—__.,— — 0.0 SSS Le -0.2 ae SSS oa lll ees - 0.4 eZ - 0.6 —__._ a ee Sess 116 o—___.— ~*~ or - 1.2 Ce ee o_o 1.4 — ~ 1.8 ——___ Verne -2.0 ae (ors |e Bw { Re oN [= 2.0 +- [-2.0 — -2.0 ~ |-2.2 ft Seawardmost position of each contour ! Other more landward | 3 2) positions of a given Range contour Profile shape at end (150 hours ) of experiment 72B-06 (L/W = 3.10). Compare with Figure 45. 102 (9) 50 100 150 Cumulative Time (hr) Distance from Original SWL Intercept { ft) Figure 54. Shoreline movement in experiment 72A-10 (L/W = 3.14). Compare with Figure 50. 103 Figure 55. Distance from Original SWL Intercept (ft) —|.0-ft Contour ao (one) 10.0 15.0 — |.l- ft Contour LE Poe ee A ee ee oe Se 0) 50 100 150 Cumulative Time (hr) Comparison of the movements of offshore zone contours in experiment 72A-10 (L/W = 3.14). Compare with Figure, 51. 104 Seawardmost position of each contour Other more landward positions of a given contour SSCS \ oO ° SF — aS SSS ned = ey I Oe = eT a ee) pe c “TT en sue, MOI 3j i agape EEOC -0.4 = -0.6 a -0.8 So fs) === ——— Soe =/.0 c ©“ Saas Sr eeea Ste -1.1 rs Cpe ee ee ey -1.2 = -1.4 %/ =O —}55) Ee ae -@-~~~e----2 =| - 1.3 ) 2) E Woe alee e Oran Gage eS 1S lel o 10 _o-8---- c ti ° oO — (<0) @ wv (an) fe ee ee = || 2Of ee Range Figure 56. Profile shape at end (80 hours) of experiment 72A-10 (L/W =*3.14). Compare with Figure 51. 105 Q n Nn (eo) 50 100 150 Cumulative Time (hr) Distance from Original SWL Intercept ( ft) eo} Figure 57. Shoreline movement in experiment 72A-06 (L/W = 5.23). Compare with Figure 54. 106 effect, since this effect was not seen for this wavelength in the wider tank. Lateral variations in the position of contours in the inner off- shore are shown in Figure 58. Lateral variations at the toe of the profile are shown in Figure 59, which compares the movement of selected contours, and in Figure 60, which is a contour map of the final profile. 4. Water Temperature Effects. a. Processes. Since the 10 LEBS experiments were conducted in an outdoor basin, water temperature was an uncontrolled variable, varyin from 4° to 31° Celsius, the dynamic viscosity varying from 3.30 x 107 to 1.64 x 107° pounds-second per square foot (1.61 x 10°23 go O80 8 107° grams-second per square centimeter) (Daily and Harleman, 1966). Vis- cosity is known to affect the fall velocity of sediment particles in settling tubes: as the viscosity of water increases, the fall velocity decreases (see Fig. 4-31 in U.S. Army, Corps of Engineers, Coastal Engi- neering Research Center, 1977). Since viscosity has been shown to have several effects on sediment transport in unidirectional flow (American Society of Civil Engineers, 1975), it is likely that water temperature and viscosity would affect sediment suspension and transport in oscilla- tory flow. For example, the erosion of beaches in the winter months may not be the result of increased wave steepness alone, but perhaps due to the decrease in water temperature as well. A greater knowledge of temperature-viscosity effects on sediment transport in oscillatory flow is needed for at least three purposes: (a) to understand the effects of temperature on erosion and accretion in nature, (b) to understand the scale effects in the laboratory when relating laboratory results obtained with one temperature history to _ prototype localities with another temperature history, and (c) to under- stand the laboratory effects when attempting to compare results from a series of research experiments with one another when the water tempera- ture was not controlled. The lack of knowledge on this last point has made it difficult to prove that the lack of profile equilibrium in several of these experiments was not due to a constantly decreasing water temperature. The important effects of temperature-viscosity on sediment transport in unidirectional flow and the results on the effect of temperature-viscosity on shoreline recession and profile development in the LEBS experiments are discussed below. b. Literature Review--Unidirectional Flow. Colby and Scott (1965) found three effects of water temperature on sediment discharge: (a) Vis- cosity changes cause changes in the thickness of the laminar sublayer which affect the relationship between mean velocity and effective bed shear. (b) The vertical distribution of suspended sediment depends on the ratio between the fall velocity of sediment particles in a turbulent sediment-water mixture and the effective turbulence of the flow for sus- 107 6.0 10.0 15.0 15.0 200 -I.l-ft Contour Distance from Original SWL Intercept (ft) 20.0 =|,.2- ft Contour -1.3—ft Contour 0 60 100 150 Cumulotive Time (hr) Figure 58. Comparison of the movements of upper offshore zone contours in experiment 72A-06 (L/W = 5.23). Compare with Figure 55. 108 20 ine) (6) ~ fe) SWL Intercept (ft) 25 —2.2-ft Contour Os (o) i) (2) Distance from Original —2.3- ft Contour O 50 100 150 Cumulative Time (hr) Figure 59. Comparison of the movements of lower off- shore zone contours in experiment 72A-06 (L/W = 5.23). Compare with Figure 52. 109 “15 I | i 1.0 ft 9 @ i] 29 S999000 QP aAaNONSA = fa = = c:}) (5) ® -1.1 Ss -1.0 iy 4 w io. = -1.0 to.) ae 1.2 E : °o = — o -1.4 LS) e -1.6 pS - 1.8 ee 5 -2.0 -2.2 25 ; AA -. -2.2 Sess -2.2 ft - _»” Seawardmost pesition — of each contour 30 Other more landward positions of a given contour PROS = 351 \ I Pos) 78 Range Figure 60. Profile shape at end (135 hours) of experiment 72A-06 (L/W = 5.23). Compare with Figure 56. 110 pending sediment. The effective turbulence of the flow is evidently not affected by viscosity changes, but the fall velocity of sand in turbulent water (nearly the same as the fall velocity in still water) is directly related to viscosity. The temperature effect is greatest for particle sizes between 0.25 and 0.5 millimeter and next greatest for the 0.125- to 0.25-millimeter range, and the effect increased with increasing depth. (The sediment used in the LEBS experiments had a ds5g of 0.22 to 0.23 millimeter.) (c) Changes in viscosity affected the fall velocity which changed the ds5q of the bedload and thus the bed forms. (The size dis- tribution of the SPTB sand was narrow, so this effect would be negligible. Changes in bed form change the resistance to flow and thus the sediment discharge. Temperature effects in both directions were found; i.e., sediment discharge both increased and decreased with increasing tempera- ture. Taylor and Vanoni (1972a, 1972b) examined temperature effects in both low- and high-transport flows, and they also found temperature effects in both directions in each case. For low-transport flow, Taylor and Vanoni found that the direction of the effect was related to position on the Shields curve (Fig. 2.45 in American Society of Civil Engineers, 1975; shear stress versus boundary Reynolds number) where the Shields curve slopes down, increasing tempera- ture caused increasing sediment discharge; where the Shields curve slopes up, increasing temperature caused decreasing sediment discharge; and where the Shields curve is flat, increasing temperature caused no change in discharge. For high-transport flows, they found that the effect was related to particle size: for the particles finer than 0.135 millimeter, suspended- sediment concentrations at all depths increased with increasing tempera- ture; for particles coarser than 0.135 millimeter, the concentrations at all depths decreased with increasing temperature; but for particles with a ds59 of 0.135 millimeter, concentrations at the higher elevations increased with increasing temperature and at the lower elevations decreased with increasing temperature. c. LEBS Results--Oscillatory Flow. Those results for unidirectional flow point out the complexity of the temperature effect, so it is not un- reasonable to expect a complex temperature-viscosity effect on sediment transport in oscillatory flow. These experiments were obviously not designed to study temperature effects since temperature was uncontrolled, but they do indicate the potential for temperature effects. Temperature changes are compared to the shoreline recession rate and volume erosion rate in the discussions that follow. Because the backshore slope was not flat the volume erosion and profile development rates were propor- tional to the square of the shoreline recession rate in these tests. (1) 1.50-Second Wave. In experiment 72C-10 (Fig. 61) the shore- line recession rate was decreasing, which means that the volume erosion rate was decreasing or near constant, while the temperature was gradually falling. A Distance from original SWL intercept (f+) Figure 61. 20 ecco Range Water )) Temperature 50 100 150 Cumulative Time (hr) Comparison of daily mean water temperatures and shoreline positions in experiment 72C-10. ll2 Temperature (°C) (2) 1.90-Second Wave. The most dramatic evidence for a tempera- ture effect was in experiment 70X-06. At 22 hours the water temperature dropped from 28° to 18° Celsius and the shoreline recession rate increas- ed from 0.06 to 0.14 foot per hour (Fig. 62,a). (After sand feeding was begun the experiments had little value to this analysis.) In experiment 70X-10 (Fig. 62,b) temperature data collection did not begin until 38 hours and the comparison of shoreline recession and temperature between 38 and 62 hours is not very conclusive. The temperature was fairly high (25° to 30° Celsius) and the shoreline recession rate was 0.08 foot per hour. In experiments 71Y-06 and 71Y-10 (Fig. 63) the shoreline recession rates were high during the first few hours (0.113 foot per hour in ex- periment 71Y-06 and 0.133 foot per hour in experiment 71Y-10). However, the shoreline recession rate soon decreased to 0.025 foot per hour in experiment 71Y-06 and 0.016 foot per hour in experiment 71Y-10, although the temperature remained at a high value. The recession rate remained constant throughout the remainder of the experiments, even though the temperature dropped sharply several times, which tends to disprove the effect suggested by experiment 70X-06. However, the mutual agreement between experiments 70X-06 and 71Y-06 is important. Between 10 and 50 hours the recession rate was quite high in experiment 70X-06 while the temperature dropped and the recession rate was much lower in experiment 71Y-06 while the temperature remained high. In experiment 72D-06 the shoreline retreated at a rate of 0.05 foot per hour, which means that the volume rate of erosion was continually increasing, while the temperature decreased from 20° to 6° Celsius (Fig. 64). The erosion of the trough in the inshore zone after the shoreline recession stopped occurred when the temperature was at its lowest values. (3) 2.35-Second Wave. In experiment 72B-06 (Fig. 65,a) the shoreline was stable and the profile was at equilibrium, even though the temperature took two 8° drops. In experiment 72B-10 (Eig; (65), b)) the shoreline retreated at a very slow rate, which varied between 0.004 and 0.018 foot (0.12 and 0.55 centimeter) per hour, while the temperature varied between 30° and 20° Celsius, with drops of 5° and 9°. Compared to the 1.90-second experiments (Figs. 62, 63, and 64), the temperature remained fairly high and the recession rate was small. (4) 3.75-Second Wave. In experiment 72A-06 (Fig. 66,a) the shoreline recession rate was constant, meaning that the volume erosion rate was increasing, while the water temperature increased. In experi- ment 72A-10 (Fig. 66,b) the shoreline was stable as the profile was at or near equilibrium and the temperature rose initially and then remained fairly constant. (5) Discussion. Experiment 70X-06 supports the hypothesis that decreasing water temperature causes increasing erosion. Although the shoreline recession rate did not respond to sharp drops in temperature in experiments 71Y-06, 71Y-10, 72D-06, 72B-06, and 72B-10, the comparison of those experiments with 70X-06 supports the general hypothesis that the 113 Distance from Original SWL Intercept (ft) 1 Sand feeding begun fan / | Water Temperature 50 100 Cumulative Time (hr) a. Experiment 7OX—06 50 100 b. Experiment 7O0X—10 Figure 62. 150 150 30 RANGE — 03—-— (See ? 20 0 200 290 200 250 Comparison of daily mean water temperatures and shoreline positions in experiments 70X-06 and 70X-10. 114 Temperature (°C) (Jo) aunjosadway 0 Ol 02 Of Ol 02 0¢ “OL-ALZ pue 90-AIZ SqUowtTredxe ut suotztsod suTTOLOYS pue soinjzetodwe, 193em ueow ATTep Fo uostzedwojD ‘¢9g ouNdTY (4y) aut aalyojnwng O00b ose 00¢ 0S2 002 OSI 00! 0S ainjDsadiuay 4aJD0M OI-Al2Z juawisedxg aN C\ Ee ee SY (14) ¢dadzajuy TMS JOulbisQ wosy aouD}sig 1S \ oO Water Temperature ZN < : : a J MC \ Shoreline Position Distance from Original SWL Intercept (ft) ro) (6) 50 100 150 200 Cumulative Time (hr) Figure 64. Comparison of daily mean water temperatures Temperature (°C) and shoreline positions in experiment 72D-06. 116 35 T (43) 4dadsaju} (O-) eunyosedwa, wo = * 100 50 Cumulative Time (hr) a. Experiment 72B—-06 5 te) TMS joulbisQ wos Goud, SIG -10 (De) e4nposedwes £ Je e ® Qa S E i“ 2 (S) S [) (13) 4d922e4u) TMS JOUIBI4Q wos edUDj81G Cumulative Time (hr) b. Experiment 72B—10 Comparison of daily mean water tempera- tures and shoreline positions in experiments 72B-06 and 72B-10. Figure 65. UI a i Temperature (So) 9 | 2 |:72A-06 © S 8 ~— = (One 2 10 50 100 150 2 S Cumulative Time (hr) = = a ic E 5 30° E ® = 3 = = @ [S) (= oO w 20 2 10 O 50 100 150 Cumulative Time (hr) Figure 66. Comparison of daily mean water tempera- tures and shoreline positions in experiments 72A-06 and 72A-10. 118 higher the temperature the lower the recession rate. Too little useful data are available in experiment 70X-10 to be of any value to the com- parison. Experiment 72A-06 supports the opposite hypothesis that an increasing water temperature causes an increasing erosion. Experiment 72C-10 sup- ports this hypothesis or perhaps tends to disprove the other hypothesis in that a decreasing water temperature coincided with a decreasing ero- sion rate. Experiment 72A-10 supports either hypothesis since the temperature and the shoreline were both stable. 5. Other Laboratory Effects. The known causes of laboratory effects are summarized in Table 14, classified by physical constraint and by phenomena or parameter affected. The effects of re-reflection, wavelength-to-tank width ratio, transverse waves, and circulation between antinodes were discussed earlier in this section. Secondary waves were observed on the wave records and their effect in a few of the experiments was discussed. Hulsbergen (1974) provides a detailed description of the effects of secondary waves on profile shape. Water temperature was measured and some of the possible effects of changing viscosity were measured, but the results are incon- clusive. Cross waves were observed for a short period of time but their effect could not be measured. Four other phenomena can cause laboratory effects, depending on the physical constraints of the individual experiment or facility designs. When conducting experiments in a wave basin with training walls and with the waves approaching the shoreline obliquely, the waves reflected from the profile can re-reflect from the down-drift sidewall, then from the generator, from the up-drift sidewall, and then reattack the profile from an entirely different angle. In similar experiments without train- ing walls, re-reflection problems are minimal but diffraction effects and basin resonance become significant sources of variations. Fairchild (1970b) discussed these three interrelated phenomena and their effects. Another effect is the difference between a profile shaped by mono- chromatic waves and a profile shaped by irregular waves. Watts (1954) and Watts and Dearduff (1954) examined the effect of varying wave period and water level. The effect of periodic waves could be examined by repeating these experiments with a set of irregular waves having the same energy density. V. CONCLUSIONS 1. Wave Height Variability. (a) Variation in reflection from the profile was found to be the major source of wave height variability in 10 movable-bed experiments. The varying phase difference between the wave re-reflected from the 119 Table 14. Physical constraint . Tank length a. Distance to initial SWL intercept b. Initial profile slope . Tank width . Water temperature . Wave basin (waves approaching obliquely with training walls) . Wave basin (waves approaching obliquely without training walls) . Periodic wave Known laboratory effects. Phenomenon or parameter affected Ile Bo n wm SF WW 10. Tate Secondary waves from generator motion! Re-reflection from wave generator? Wavelength-to-tank width ratio“ Transverse waves2 Cross waves? Circulation between antinodes of standing wave? . Viscosity! . Sidewall re-reflection . Diffraction Basin resonance Simulation of real waves lPhenomenon observed and effects measured to a limited extent in LEBS study. 2Phenomenon observed and effects measured. 3Phenomenon observed, but effects not measured. generator and the generator motion caused a varying average incident wave height. Transverse, cross, and secondary waves also contributed to the spatial variability of the incident wave height. (b) The reflection coefficient variation ranged from moderate to significant in the movable-bed tanks, ranging from 0.02 to 0.12 in ex- periment 72C-10 and from 0.04 to 0.27 in experiment 72D-06. In the fixed-bed tanks, which is an indication of the measurement accuracy in the movable-bed tanks, Kp ranged from 0.01 to 0.02 in experiment 72C-10 and from 0.02 to 0.09 in experiment 72B-10. (c) Waves are reflected by the runup on the foreshore, a plunging- type breaker, and any segment of the submerged profile where the depth change is Significant. Variations in the steepness and top elevation of any submerged siope can cause significant variations in Kp. The distance between two reflecting zones can affect the phase difference between waves reflected from the two zones and thus affect the Kp measurement seaward of the profile. The important source of Kp vari- ability in any one experiment did not appear to be a function of the wave period. The steepness of the submerged slope was an important source of variability in all experiments except 72A-10, and the increas- ing foreshore berm elevation was the primary source of variability in only experiment 72A-10. Variations in the elevations of the top of the submerged slope caused significant Kp variability in experiments 71Y-06, 72D-06, and 72A-06. The increasing distance between the foreshore and submerged slopes caused some Kp variability in all experiments with the 1.90-second wave and was the primary source in experiment 72C-10 with the 1.50-second wave. As the shelf length varied in each experiment, the Kp varied correspondingly. (d) The average K, from profiles which developed from an initial 0.10 slope increased with increasing wavelength (or wave period). (e) The average K, of the 1.90-second wave increased, rather than decreased, as the initial profile steepness decreased. (f) Reflection coefficient variation was less than 0.05 during the last 25 hours of the three experiments which appeared to be at or very near equilibrium, but this does not conclusively prove that K, varia- bility is eliminated on an equilibrium profile. (g) In all experiments except 72C-10 the K, tended to increase during the experiment indicating that the profile adjustment tended toward reflecting, rather than absorbing, energy. (h) Incident wave height, H;, measurements in the fixed-bed tanks were indicative of the measurement errors in the movable-bed tank. H range in the fixed-bed tanks was as little as 0.03 foot in five experi- ments, and as much as 0.07 foot in experiment 72A-06. (1) The effect of varying re-reflection on the incident wave height in each experiment was calculated by subtracting the range of heights in I2| the fixed-bed tanks from the range of heights in the movable-bed tanks. In the 6-foot tank, this effect ranged from 0.01 foot in experiment 72B-06 to 0.03 foot in the other four experiments. In the 10-foot tank, this effect ranged from 0 in experiment 72B-10 to 0.08 foot in experiment 72A-10. This implies that the wider tank may amplify this re-reflection effect. (j) The importance of phase difference between the reflected wave and the generator motion to the incident wave height variability is seen best by comparing experiments 72B-06 and 72B-10. The average Kp in experi- ment 72B-06 was 0.08 and in experiment 72B-10 was 0.17, which means that the reflected wave height was greater in the 10-foot tank. However, the average incident wave height was 0.38 foot in 72B-06 and only 0.31 foot in experiment 72B-10. Since the difference in reflected wave height would not have caused that difference, only the phase-difference effect resulting from the difference in initial test length can account for the difference. 2. Profile Equilibrium. (a) In two experiments with all parameters the same except the initial slope (0.05 and 0.10), the final profiles had quite different slopes, although neither reached equilibrium. This further verifies the conclusion of Collins and Chesnutt (1975, 1976) that the initial profile influences the final stable profile shape. (b) In two pairs of experiments with the same wave condition but different tank width and initial test length, one experiment in each pair reached equilibrium; the other experiment in each pair developed a different shape which continued to adjust. Laboratory effects are the apparent causes for the differences. (c) Profile equilibrium is not easily attained. Two of four summer profiles and the one winter profile reached equilibrium, but none of the five profiles in the transition category (0.020 < H,/L, < 0.025) reached equilibrium, indicating that profiles for waves in the transition region are more unstable. 3. Laboratory Effects. (a) The initial profile slope affects the profile development at least partially as a result of differences in the phase of secondary waves at the toe of the profile. (b) The initial distance from the generator to the shoreline is an important experimental parameter. Differences in this distance affect the phase difference between the reflected wave and the generator motion and thus affect the incident wave height. The effect of varying incident wave height on profile shape is opposite to intuition; in experiments with the same wave condition and different initial distance to the shore- line developed, the higher erosion rate was associated with the lower |e average H,. Differences in this distance also affect the phase of secondary waves at the toe of the profile. The effect of secondary waves was shown by differences in the shape of the offshore zone in two pairs of experiments. (c) Three special and one general tank width effects were observed. Strong circulation currents developed over the profile between antinodes of the standing wave for a wavelength four times the tank width, which affected the profile development and reflectivity. Cross waves occurred over a short segment of the profile for a brief time in one experiment, but the effect was not measured. Transverse waves generated by the gap at the end of the generator blade caused significant lateral variations in one experiment, but were not observed in the experiment with the same wave period but different tank width and initial test length and without a gap. In general, as the wavelength-to-tank width ratio increased from 1, the amount of lateral variation in profile development decreased. (d) Two different effects of water temperature variation were observed. Six experiments support, to varying extents, the hypothesis that the higher the water temperature, the lower the recession rate. Two experiments support the opposite effect, that the higher the water temperature, the higher the recession rate. Another experiment supports either hypothesis. VI. RECOMMENDATIONS FOR CONDUCTING MOVABLE-BED COASTAL EXPERIMENTS 1. Modeling Criterion. Equilibrium profiles are not often found in the prototype, and thus they may not be necessary to replicate. Also, equilibrium profiles are difficult to attain in the laboratory and may not be repeatable when they are reached. Therefore, it is recommended that some other criteria be selected as the prototype condition for replication in the laboratory, such as constant rate of shoreline recession or volume erosion. 2. Tank Setup and Test Conditions. (a) The initial distance from the generator to the shoreline must be held constant when attempting to perform repeatable profile experiments. (b) The initial slope can affect the profile development and should be held constant to assure test repeatability. (c) To eliminate lateral variations in profile shape due to too short a crest length, wavelengths greater than three times the tank width should be chosen. However, two-dimensional tests may distort a three-dimensional problem to an unknown extent. (d) The water temperature should be kept within a 5° Celsius range to assure test repeatability. 123 (e) Cross waves in the constant-depth section and transverse waves can be avoided by careful selection of wave period and water depth for each tank width (Barnard and Pritchard, 1972; Madsen, 1974). (f) Secondary waves in the constant depth section can be eliminated by programing the generator motion with elliptic functions or by the use of sills placed at the proper location along the tank for each wave period (Hulsbergen, 1974). (g) Variability in profile reflectivity, generation of secondary waves over a shelf, and generation of cross waves over profile segments are phenomena which cannot be avoided or eliminated, but the experi- menters should be aware of the potential of these phenomena to affect profile development. (h) As a minimum the experimental conditions discussed in this series of reports should be documented in each movable-bed coastal engineering experiment and model study. 3. Future Investigation. (a) The hypotheses on sources of profile reflectivity variability should be examined one-by-one in fixed-bed experiments. (b) More research is needed to quantify the effect of the initial profile slope on the final profile shape. (c) More research is needed on how wide a tank must be to assure that the tank walls do not affect a significant part of the profile. (d) More basic research is needed on the effect of water tempera- ture on sediment transport in oscillatory flow. 124 LITERATURE CITED ALLEN, R.H., '"'A Glossary of Coastal Engineering Terms,'' MP 2-72, U.S. Army, Corps of Engineers, Coastal Engineering Research Center, Washington, D.C., Apr. 1972. AMERICAN SOCIETY OF CIVIL ENGINEERS, "Sedimentation Engineering,'' ASCE Task Committee for the Preparation of the Manual on Sedimentation, New York, 1975. BARNARD, B.J.S., and PRITCHARD, W.G., "Cross-Waves. Part 2, Experiments," Journal of Flutd Mechantcs, Vol. 55, Pt. 2, 1972, pp. 245-255. CHESNUTT, C.B., "Laboratory Effects in Coastal Movable-Bed Models," Proceedings of the Sympostum on Modeling Techniques, 1975, pp. 945-961. CHESNUTT, C.B., and GALVIN, C.J., Jr., ''Lab Profile and Reflection Changes for Ho/Lo = 0.02," Proceedings of the 14th Conference on Coastal Engineering, 1974, pp. 958-977. CHESNUTT, C.B., and STAFFORD, R.P., "Movable-Bed Experiments with Ho/Lo = 0.021 (1970)," Vol. II, MR 77-7, Laboratory Effects in Beach Studies, U.S. Army, Corps of Engineers, Coastal Engineering Research Center, Fort Belvoir, Va., Aug. 1977a. CHESNUTT, C.B., and STAFFORD, R.P., 'Movable-Bed Experiments with Ho/Lo = 0.021 (1971)," Vol. III, MR 77-7, Laboratory Effects in Beach Studtes, U.S. Army, Corps of Engineers, Coastal Engineering Research Genter ys Kort Belvoir.) Vale.) NOV LOND. CHESNUTT, C.B., and STAFFORD, R.P., 'Movable-Bed Experiments with Ho/Lo = 0.021 (1972)," Vol. IV, MR 77-7, Laboratory Effects tn Beach Studtes, U.S. Army, Corps of Engineers, Coastal Engineering Research Genter, Fort Belvoir, Va., Dec. 1977c. CHESNUTT, C.B., and STAFFORD, R.P., "Movable-Bed Experiments with H,/Lo = 0.039," Vol. V, MR 77-7, Laboratory Effects in Beach Studies, U.S. Army, Corps of Engineers, Coastal Engineering Research Center, Rope Welkvonsen Wels 5 Dees OW 7ele CHESNUTT, C.B., and STAFFORD, R.P., ''Movable-Bed Experiments with Hj/Lo = 0.004," Vol. VI, MR 77-7, Laboratory Effects in Beach Studies, U.S. Army, Corps of Engineers, Coastal Engineering Research Center, Fort Belvoir, Va., Mar. 1978a. CHESNUTT, C.B., and STAFFORD, R.P., 'Movable-Bed Experiments with Ho/Lo = 0.013," Vol. VII, MR 77-7, Laboratory Effects tn Beach Studies, U.S. Army, Corps of Engineers, Coastal Engineering Research Center, Fort Belvoir, Va., March 1978b. 125 CHESNUTT, C.B., et al., "Beach Profile Development on an Initial 1:10 Slope of 0.2 Millimeter Sand," Transactions of the American Geophysical Unton, Vol. 53, 1972, p. 411. COLBY, B.R., and SCOTT, C.H., "Effects of Water Temperature on the Discharge ioe Bed Material, n Professtonal une 462-G, U.S. Geological Survey, Washington, D.C., 1965. COLLINS, J.1., and CHESNUTT, C.B., ''Tests on the Equilibrium Profiles of Model Beaches and the Effects of Grain Shape and Size Distribution," Proceedings of the Sympostum on Modeling Techniques, 1975, pp. 907-926. 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WATTS, G.M., and DEARDUFF, R.F., "Laboratory Study of Effect of Tidal Action on Wave-Formed Beach Profiles,'' TM-52, U.S. Army, Corps of Engineers, Beach Erosion Board, Washington, D.C., Dec. 1954. 127 g°A “/-// *ou amp g cn €02OL "g cA ‘{-LL *0u J10dei snosueTTeostW *1oqUeD Yyo1eesoy suy~toeutsugq ~Teqseo9 “S°M :SeTzes “IT “eTITL “I ‘szuezanD *g «‘syueQ eARM °C = *Si10qe10Ua3 SARM "7 “UOTIIETJOT BAPM “E “SAOYPeAg *Z ‘“BuTAseuTZue Teqseon *| *queudoTeaep eTtyoid pajoezze ‘seinjzerodwaq 103eM pue ‘yApTA yueq ‘ya3ueT 3Se} [TeTITUuT ‘sedo,Ts aTtTyoad [TerqTUT ut Seouetesjftp Aq pasneo *sqoezjzo AtojeIOGeT *170°Q JO sseudaejzs saeM e YQTM Sjuowttedxsa SAT UF ATAeTNOTIIed ‘poutejjze ATTsea Jou sem wntzqrptInba eTTyorg “squoltiedxe peq-eTqeaow QO, ut AqTTTqetTaea AYy8tTey eaem JO 302n0s Azewtid ay} sem peqsnfpe eTfTyoad ayq se uotqzeTAeA UOTIIeTJeI aAeH (8 °A */-/£ *ou £ azaqUeD YyoTeesoy SuTiIveuTsuq Teqseop *s*g — j10dez SnOoueTTe0STW) “TTT : “d /Z] "8L6L ‘e0TAIES uot eUAOFUYT TeoTuYyIe], TeuoTIeN woaAF oTqeTTeae : *eA ‘plTatzZutads $ teqUeD yoTeesey SuTAssuTsuq TeqIseog *Ss*n : “eA S1TOATAg OSy ei — "Janusey) *g seTzeyo Aq / squewtiedxe peq-eTqeaow OQ, woaz sqtnsair jo stsfTeuy “IIIA owNToA ‘*seTpnis yoReq UT sqoezze A10ReIOGET “gq seTazeyg £74nusayD £09 L729 B°A “7-21 “OU aur1g cn” £0¢OL “9. °A “{-LL ‘ou Jaode1 snosueTTeosTW ‘*1ejJUeQ YyOIResoy BuTiseuTSuq Te3seoD “S°N :SeTteS “II “eTITL *I “*sqzUezIND *g “*syUeRZ DAeM *G = *S10Re1OUES BABM “7 “UOTJIETJOI ARM *E “SASYPeAgG *Z ‘BSuTAseuTZue TeqIseoD *| *quowdoTeaep eTtTjord paqjoeysje ‘seinjetodue} z0jzem pue ‘ypTA yueQ “yq8ueT 3seq TeT}yTuT ‘sedoTs eTTyJozd TeTjTuT ut saouerezstp Aq pesneo “sqoejyea Atoje10qeT *170°Q JO sseudseqzs oaeM e YATM squoutazedxe @ATF UT ATAeTNOTIAed ‘pautTeqje ATTsee Jou sem wntAqt{Ttnbe eTtjorg ‘sjueutiedxe peq-eTqeaow Q,| ut AIT[TTqeTIeA AYSTey aAeM Fo voANOS Azewtad 9y3z sem paqsnf(pe ettyorzd ay, se uotzeTAeA uoTIEeTJeI BAe (g "A /-// *ou $ az9}UaDg YyoITREeSZy SuTiseuTsug Te3seog *S'n — Jzodea snosueTTeostW) “TTT : *d /Z1 "8/6, Se0TAIaS uoTJeWAOFUT TBITUYDe] TPUOTIeN WOTF eTqeTTeae : ‘en ‘ptoatyFsutads $ 19}Ue9 YyOIeesey BuTAseUTZUy TeIseoD “s*p : “eA SATOATOG *34 — "q3nusey) *g seTieyQ Aq / sjueutTredxe paq-eTqeaow Q| wory sq[nse1r jo stshTeuy “[IIA ewNTOA ‘“seTpnjs yoveq ut sqz0azza AZOReIOGET "gq seTazeyp ‘34nuseyD Lc9 g°A “7-/2 *ou aug cn” €0720L ; “9 ¢A *{-LL ‘ou 310de1 snosueTTeosTW *‘1eqUeD YyDIeasoy 3uTAdeUTSUq TeISeOD “S°N :SeTteg “IT “eTITL “1 “squezing ‘9g «‘syueq aaeM *G *Si0qe10Ua3 SAEM “7 YUOTIOSTFOT ARM *E “*SAOYPeIg *Z ‘BuTisauT3ua [eqyseo) *| *jJueudoTsasp eTTzoid pejoezze ‘sainjerzadweq 10,em pue ‘yqpIM yue3 “yq3ueT 3S03 [TeTITuT ‘sedoTs eTtTyoad TeT3TUT uz seouereszTp Aq pasneo “sq00jjo AzojeIOGeyT *170°Q JO sseudseqs oAPM e YITM sqUeMTIadxa PATF UT ATAeTNoTIZed ‘poutejje ATTSea Jou sem wntzqtTInba eTTjoIg “squoutiedxe peq-eTqeaow Qg, ut AATTTGeTAeA AYZToeYy asAeM Jo aDAINnN0S Azewtaid 94} sem pojsnfpe aTtjoid ayj se uoTqeTazeA UOT}IETJeI aAeH (8 *A *f-/f ‘ou £ taqUaD YIesSey BSuTroeuTsugq TeIseog *S*n — q10de1 snosueTTeoSTW) “TTT : *d LZL "8161 ‘e0TALeS uoTJeWAOFUT TEOTUYOeT TeUOTIeN WoOAF sTqeTTeae : “eA ‘pTaty3utads $ Jequeg yoieesoy BuTieeuTsuq Teqyseog *s*n : “eA SATOATeg 14 — *}4nuseyD *g seTIeYyD Aq / squewtTiedxe paq-aTqeaow Q| woarz sz [Nsea jo stshTeuy “IIIA ewNTOA ‘seTpnqs yoreq ut sqIeFze A10ReI0qGe “gq setTazeyg ‘24nusayD L279 g°A Sf *OU AMES oN £0201 "9 a *{-LL *ou j310de1 snosueyTTaosTW ‘1eqUueQ yorReesoy BuTseuTSug Te ISeOD "S°N :SeTIeS “II “eTITL “I “squeazInD *g ‘*syUeW aAReM *G *S10Re19US BARM *Y “*UOTJIATFOI AEM “E “SABYyeoeTg *Z *B3upasveuTSue Te seo) *| ‘queudoToasp eTtyord pajoeszse ‘seinjeiadueq aoqem pue SyypTA yueR *yq3ueT 3893 TeTITuT ‘sadoTs aTTjoad [etqILluT ut seouerezstp Aq pesneo *sqoezja AzojzerOGeT *[7Z0°O Jo ssaudseqs aaeM e YITM SquUoUTiedxa @ATJF UT ATAeTNOTIIAed ‘Speutejje ATTsea Jou sem wntiqt{Ttnbe eTTjor1g *sjuowtiedxe peq-eTqeAaow Qt ut AATTTqeTaeA ZYyZTeYy eAeM FO |9oINOS Azeutid ay, sem paqsnf[pe epTtjoad ay} se uoT}eTAPA UOTIIETFOA OAH (8 “A Sf-// sou £ zaqueD YyoIeesey Sutieoursug [Teqseog *s' — 3aodex snosueTTeosTW) “TTT : ‘d /ZL "8L6| ‘a0TAIES uotT}eurOfFUuy TeoTuyos] TeuoTIeN wWoLF eTqetteae : ‘eA ‘pletysutads ! 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