Yo!. G Mb. / DEPARTMENT OF THE ARMY CORPS OF ENGINEERS THE BULLETIN OF THE BEACH EROSION BOARD OFFICE, CHIEF OF ENGINEERS WASHINGTON, D.C. VOL. 8 JANUARY 1, 1954 NO. 1 i" ah ‘ M hy WAR kL Came 7 AY i hei ; eh if th Wignis NM AMM ii 5} Panel eau avn Rca au ip Nie TABLE OF CONTENTS Page RIPPLE TANK STUDIES OF THE MOTION OF SURFACE GRAVITY-WAVES @esoeegeeoeveeeeveoe ee eoeeeoeeseveee02 8028000880808 1 PROGRESS REPORTS ON RESEARCH SPONSORED BY THE BEACH EROSION BOARD @eeceoeevneeeeseeeereoeeeeoereoe ee alk BEACH EROSION STUDIES eiaieislei cvareiareleieieinvevereiereieicie e-eretetorerete 27 DEPARTMENT OF THE ARMY CORPS OF ENGINEERS BEACH EROSION BOARD Vol. 8 1 January 195) No. 1 mn ll AIAN IU 0044904 7? ela. eet iy Bo Ree ey rearcrae e Ocg ew ok RIPPLE TANK STUDIES OF THE MOTION OF SURFACE GRAVITY-WAVES by Osvald Sibul, Dept. of Engineering, University of California Technical Report Series 3, Issue 346, Institute of Engrg. Research, Wave Research Lab. - prepared under contract with the Office of Naval Research. INTRODUCTION Ocean waves are generated by the action of wind blowing over. the surface of water. The winds are irregular in their intensity, direction and duration and the result- ant waves vary in period, height and direction of travel. When we consider also the extreme difficulties one encounters in measuring the waves in nature, and the effect of hydrography on wave characteristics, then it oan be appreciated how greatly the investigator is handicapped in his study of wave action and how moh model studies are needed in many instances in order to understand the basic laws of wave motione One of the most useful units to the engineer in this regard is the ripple tank, which as a laboretory instrument permits the study of wave prob= lems involving refraction, diffraction, reflection and decay of waves. It is also reliable and handy for demonstration purposes, for it shows, within the field of vision of an engineer, phenomena which in the prototype might cover many square milése EQUIPMENT Ripple Tanks The ripple tank used in this study is located in the Fluid Mechanics Laboratory of the University of California, Berkeley, California (Fige 1). It is 442. inches wide, 20 feet long, and 5 inches deepe The tank is made of aluminum, except the middle section of the bottom which consists of a- glass plate, 3/8 inches thick, for observation. A point source light consisting of a 250W mercuryvapor lemp is located underneath the channel at an optical distance of approximately 10 feete 4. mirror set at 45° to the horizontal reflects the light 90° to an. observation soreene A schematic diagram of the ripple tank is shown in Figure 2e The screen consisted of a piece of tracing paper stretohed to a 60 inch by 60 inch wooden frame. It was located directly over the glass section of the ripple tank between two guides (one on each side of the tank) and could be raised or lowered by means of strings and pulleys for the purpose of focusing the wave images on the screene The theory of the optical system is based on the fact that when light passes through a disturbed water surface, it will not be uniform in intensity due to the varying angle of refraction at the surface. A wave acts as @ lens and concentrates light at the wave crests; hence the wave crests are represented by bright bands in the photographse Photographic Equipments The camera used was a Bell and Howell “Filmo” 16 mm movie camera 70-DA f. 165 with a 15mm focal length lense The film used was Cine-Kodak Super XX high speed panchromatic safety film. Most of the motion pictures were taken at 64 frames per second (corresponding to an exposure time of 1/125 sec.) with an opening of fe 165. The distance between still-water level and the screen varied from 25 inches to 60 inches, averaging 40 inches. The distance between the screen and camera averaged 6 feet, in most cases. All the data observed during the tests are presented in Table I. Wave Generators A plunger type wave generator was usede The generator was supported by a movable frame and could be placed at any position along the ripple tank. The amplitude of the movement was controlled by an eccentric and could be varied from 0 to about 3/4 of an inche The frequency of the plunger could be varied from about 1 to 20 per second. By trial a wave steepness was selected so as to produce a series of clear images on the screen. Test Conditions: A pictorial summary of this study of wave motion in various idealized condi- tions is presented in Figures 3a through 3ge The various phenomena presented in these figures and the test conditions are summarized in Table I. DISCUSSION In water of uniform depth periodic waves are propagated with uniform velocity and without change of form. The wave crests remain parallel to each cthere This is demonstrated in Run 1 (Figure 3a). The relationship between period, length and velocity characteristics of periodic wave phenomena is HBO #650060 010060066000 60000600 0 (1) Where L is the length, C the velocity and T the period of the wares. If water of constant depth is disturbed by small periodic impulses, the weve Length and velocity are related to the depth by the equation Cs cc (2) 277 where d is the water depth. As long as the surface tension has negligible in- fluence and the wave height is small as compared with d and L, this equation applies to both deep-water and shallow-water wavese For waves where surface tension is not negligible (where the radius of curvature is very small) the velocity is given by the equation -|-e& , 227 ule Z Ogee a tanh ee ee ee ee ee we G8) where © is the surface tension in lbs/ft and J° is the density of water in slugs/ft°. Experiments by Ae Je Chinn (Reference 4), indicated that for wave lengths of 0.075 fte or less, the effect of surface tension had to be considered, but that the second term (err/SF L) in the velocity equation had to be modified. Chinn found that the average experimental results for waves in this region were 11.5% lower than indicated by the theory and in order to correct this discrepancy the term (2%7/ fL) was reduced by 40%". For the present ripple tank studies the “The author of the present report is of the opinion that this statement should be viewed with caution and that additional laboratory experiments should be per= formed, This statement is based upon the results of a few measurementse 2 potaeg eyouoidde sAem Jo WoT_Z.eI1;p S44 Sev sues 94} ST UOTZ2eAITp TeuusYyy °2Ts[ sedo[s eprs yQrIm Teuusyo qu2Tei7s pedeys=-, 6 ZUTIeque seAacy olG * *° * Yoveq eyy pue soAem SutTyouoidde ueem3eq eTZuy ET:T edoTg e*yoveq Zutrdots AyTm10jztTun KUZTeI4S B UO ZUTZOCaATeI sevcA [Tseoys Ievp[nsuezoea qdniqe us Jeao Zutssed seaey deep Ie[nsuet41, ydniqe use Jutssed seauy Teoys Fe[nsuetsy 4dniqs ue 1eao Surssed sesaay [euueyo JO euTT1e,uUeD ey, FuoTe yydep jo eZusyo 4dniqe ue st e.1eUy *ygdep 9UetesJIp FO 1e9eVM UT SOAUE ygdep UWloxyIUN Jo Ie9eMm UT SeABAL uo0tT7dt190seq SoAeM OdVTAING JO WOTIOW OYA FO satpngg Yue, epTddty eyy 1oF vpeq I @idvi eqIg*g = G2 ung °T GSe*s - 2 UY TT T°S - & els*T - og UY “IT - 6T Uy °T 8°O - BT MY °IS°O - AT OTA ST IBA 2s0°0 P P zso°o 'p (°9u0D) I TIGvi zuny °IG°’Z -— 2 UM °"jO°e — Tz ung ung £9[ ung Joy S7Gz°OQ tazepurtAo eyy gO °Wetp ey} 7nq VyUep Sus et? ITV *seaum JO Uqzue— ey, st J ereym “JT G60°0°°°a aZeputtfo Jowmetg °ST[ em [edTZ1EA W}tm rzepurtAo =v puncte Zurod seauy sutdOTS AT IU ns OLIT GI?T seyou6eq Surdots ATuxo0zTun YyyTa (TEAST 036M C4} eAOgS ZuTpuezxXe) pus[st pedwys—euoo vw punore Jufo? seAug eeJpeam oy} JO pue Jeq,O e4y 8 UOTJOVIZJTp OF0N cespem peT TUM [BOTZ1eA GB JJO Zur_ZooT Jer sevugy SOAGM JUSPTOUT ety JO WOTZOSOITP OY} OF OG} Fe PEUTLOUT ‘[ [em [BOT}IeA @ JJO ZurqZoeT Jel seAuy dvo Jo; euxe0etg ev Jurssud seauy 107-38 -yvelIq @ JO MOpuys UL Jequm deep o7UT I093M MOTTBYS WOLy ZuTQoesp seAuy °Je7VeMyeelg B JO MOpsys UL 109GM MOTT BYS OFUE zejum deep Wory ZuUTRZOCTTEP soauy moTydtasseq -wave length for each run was more than 0.075 ft.e, and in addition the surface tension was reduced to about 40 dynes/eme; hence, the Equation (2) should be valide "A In Equation (2) tanh (27% 4/L) approaches unity when d becomes large as compared with Le When d/L = 0.25 the wave velocity is 5% less than that for deep-water wavese For d/L = 0.5, tanh (2 d/L) = 0.9963 and the error in wave velocity will be negligible using the formula NE Co = a eC where tanh (27 4/1.) is taken as a unity. In most papers the waves in water having a depth greater than half the wave length are considered as deep-water waves, while waves in lesser depths are shallow-water wavese If the wave length is very large as compared with the depth, tanh (27 d/L) approaches 2 d/L and Equation (2) takes the form ¢ = fel ae oN eC Run 1 (Figure 3a) represents the condition for a uniform depth of water d = 0.04 ft. and a constant wave period T = 0624 sec. To compute the wave length for the given condition we have from Equations (1) and (2) the following equation L® ¢/27rT2 tanh (277d/L) = 5.12 T2 tanh hh (27rd/L) ~~~ ~~~ (6) In this equation L is in implicit form. To solve it, L in tanh (277d/L) should be assumed for the first approximation and the computations repeated until the equation is satisfied. This procedure is tedious; consequently, tables have been prepared to present various factors as functions of d/L, and d/L (Ref. 11). Making use of Equations (1) and (4) it is found that Legmy Sede, Eaije is ielieisieWe) .ss0)e)) (ol) elim Sin Melee so Meer iota te (7) for Run 1 (Fig. 3a) Lo = 5el2 (0024)? = 0.2949 fte and G/L = 001356 For this value of a/uy in the tables it is found that d/L ® 0.1713 which gives L » 0204/0.1713 = 00234 ft. This is in close agreement with the measured value of 0024 fte For Run 2 (Figure 3a) the channel was divided longitudinally so that, starting from a certain point, half of the channel had a depth of d; = 0.071 ft. while the other half had a depth of d m 0.027 ft. The period was the same for both of the sections (T = 0.22 sece). L, = 5012 (0022) - 0.2478 5 For the left side, Tier = 0.2865. Making use of the tables (Ref. 1) Pas ais found that dy/L = 0.30003 hence, L = 0.071/0.3000 = 00237 ft. as compared with the measursa wave length, L s 0.24 fte For the right side of the channel, de 0.027, d/Ly = 0.1090; hence d/L = 0.1488 and L = 0.027/0.1488 = 0.181 ft. which again was nearly the same as the measured value of 0.184 ft. Wave Refracticn When waves approach a beach at an angle their crests are bent, because the in- shores portion of the wave front travels in shallower water and hence, ata lower velocity than does the portion in deeper water. The bottom topography, the wave period and direction of travel in deep water determine the character= istics of refraction in shoaling water. The result of refraction is a change in weve height, length and direction of wave travel. The lengths of waves travelling over a shoaling beach is decreased due to the decreased velocity for L = C T, as T remains constant. The decreased wave length means also a concentration of wave energy and, hence, an increase of wave heights, for a ah, \ 2 Po” ER where Py and Po is the power per unit length of crest passing points land 2 and Hy and Ho are the corresponding wave heightse Thus, waves travelling over a submarine ridge usually will be decreased in length and increased in height and passing over a submarine valley will be incressed in length and decreased in height. To illustrate the refraction on a shoaling beach Run 6 (Figure 3a) was com= pleted. A uniformly sloping beach with a slope of 1:13 was introduced with an angle of 57° between the front of approaching waves and the parallel contour- lines of the beach. The refraction pattern can be seen clearly in the photo-= graph of Run 6. However, the best conception of this phenomena can be obtained by observing the moving pictures taken with a speed of 48 frames per second and then projecting them at about 1/3 of this speed. The imreased heights of the waves on the shore are indicated by the sharper crest=-lines in the photo- graphs ° Runs 3, 4, and 5 (Figure 3a) illustrate the changes in wave lengths and velocities as the waves pass over shoals of various configurations. In Run 3 the waves are passing over an abrupt triangular shoal; in Run 5 over an abrupt rectangular shoal: while Run 4 demonstrates the wave characteristics when an abrupt “invert- ed" triangular shoal is introduced. It might be stated that Runs 3 and 5 repre=- sent the wave phenomenon over a submarine ridge, while Run 4 is similar to the wave characteristics over a submarine valley. Naturally the change of the depth in the ocean usually is not so abrupte This will change the characteristics only as far as the angle of intersection of wave crest=-lines is concerned. A gradual change of depth will introduce a gradual change in the direction of wave travel, as oan be seen in Run 6, which demonstrates the refraction of waves on a sloping beache Run 7 (Figure 3b) was of wave refraction in a V-shaped channel with side=slopes of 1312. It can be seen clearly that the waves “wheel” around by approximately 90° and break on the beaches as they enter the channel. The breaking waves are indicated by relatively wide and strong white lines in the photography. Almost all of the wave energy is destroyed in breaking waves, and so the wave height is decreasing very rapidly as they advance along the channel. From this rel- atively simple experiment it can be seen that it is advantageous to use a channel with flat sloping sandy beaches to connect a harbor or basin to a body of stormy waters in order to prevent the waves from penetrating into the harbors Wave Diffraction When a wave train is interrupted by a breakwater or similar barrier a sheltered region is formed. The phenomenon by which water waves are propagated into this sheltered area is called diffraction. A knowledge of the diffraction phenomenon hes important application in the design and location of breakwaters in connection with harbor development. It also has & bearing on the distribution of wave energy along beaches located in the lee of headlands and offshore islands. The phenomenon is analogous to the diffraction of light, sound and electromagetic waves, and theories for breakwater diffraction have been adapted from those theoriese Basically there are two types of diffraction problems, connected with breakwaters s (i) Diffraction around the end of a semi-infinite impermeable barriere (ii) The passage of waves through a breakwater gape No exact solution has been found for the case of a barrier of finite length, but it is believed that satisfactory results can be obtained by using the solution of semi-infinite barrier for each of the ends. It has been found that this assumption is allowable only in the case where the length of the barrier is long compared with the wave length (see also the section under “Islands"). The theory of water wave diffraction will not be presented here as this is readily available in the literature. The purpose of this paper is to demon- strate visually, by photographs and moving pictures, the wave=characteristics when diffraction occurs at various types of obstacles. In Runs 8 and 9 (Figure 3b) a semi-infinite breakwater was introduced. Run 8 demonstrates the diffraction pattern from deep into shallow water around a breakwater tip. An abrupt change of depth was introduced along the geometrical shadow of the breakwater and the depth of the water in the shadow was about 3/6 of that outside. It can be seen that the wave-crests in the lee of breakwater are almost straight, up to a line drawn about 20° from the tip of the breakwater to the geometrical shadow. From here on the wave crest assumes an almost circular form, with the center at the tip of breakwater. Run 9 (Figure 3b) demonstrates diffraction around a semi-infinite barrier, from shallow-water into deep water. The depth of water in the shadow section behind the breakwater is about 5/3 of that outside. As in the photographs, the height of diffracted weves in deep water is very small as compared with the incident waves. This is indicated by the wide, low contrast, crest-linese The circular ff form of the wave crest in the lee of breakwater is distorted again by a short, almost straight portion of crest, connecting the more advanced circular crest in deep-water and the incident wave in shallow water. The change from a straight crest to a ourved one appears to be more abrupt than in Run 8 However, the diffraction pattern depends greatly upon the ratio of water depths in the lee of breakwater to the depths outside. For the uniform depth of water it would be expected that the wave crests in the shadow of the breakwater would assume an almost circular form, with their senter at the tip of breakwater. As for the heights of diffracted waves = shallow water in the lee results in higher diffracted waves than if deep water sxists in that area. Some breakwaters have gaps through which vessels may enter sheltered waterse When waves pass through @ gap, diffraction occurs at the two ends of the gape In the case of a relatively narrow gap (compared with the wave length), the diffraction of waves in the lee of breakwater will be different than that around a semi-infinite breakwater tipe Theories have been developed for this condition (Ref. 3 and 10) and generalized diagrams developed by Johnson (6) for various conditions of wave approach and wave length. These diagrams can be used as transparent overlays, and by moving them over a chart of a harbors the location of the breakwater to give the most desirable protection can be obtained. It has been found that when the gap width is in excess of about five wave lengths, the diffraction patterns at each side of the opening are nearly inde=- pendent of each other. In such cases the pattern given for a semi-infinite breakwater can be used to estimate the height and direction of waves on the leeward side. As a comparison, it might be mentioned here, that this fact seems to be valid also for the diffraction pattern around the ends of a finite-length breakwater. , This has been demonstrated in Runs 15 to 25 (Figures 3f and 3g) wherein waves /diffracted around a vertical walled cylinder. When the diameter of the cylinder approached 6 wave lengths, the diffraction patterns around each of the ends appear to be nearly independent as far as the alinement of the wave crests is concerned. This fact is discussed further in the section on “Islands”. Run 10 (Figure 3b) was made to demonstrate diffraction at a breakwater pepe A breakwater was introduced which extended completely across the tank, with an opening of about 1.2 wave lengths wide in its center. The water depth was uni- form and the wave period was T = 0022 sece The nearly circular wave pattern, with center in the middle of the gap, canbe observed in the photograph. The shange of wave heights is indicated by the intensity of white crest-linese The waves were relatively high close to the gap and along a line parallel to the direction of wave approach and passing through the center of the gape The wave height decreased rapidly within the shadow of the breakwater in the direction perpendicular to the direction of wave advance, and less rapidly in direction of wave approache It has been shown by Putnam and Arthur (Ref. 2) that the geometrical shape of the breakwater tip, within the limits of their investigation, had no material influence on the wave diffraction pattern. With a sharp corner, it was observed that a secondary disturbance originated at the corners with propagated capillary wevas with a circular pattern superposed upon the main gravity-wave system. This is very clearly demonstrated in Run 10 (Figure 3b). A better conception of this phenomenon can be obtained by observing the movies of this rung however, the pattern can be distinguished also in the photo shown in 8 Figure 3be Rounding of the corners will practically eliminate t'5 sezondary capillary wave systeme This is demonstrated in Run 12 (Figure 5h) wherein diffraction occurs around the leeward end of a vertical-walled wougee Wave Reflection Wave motion in harbor basins often is inoreased due io waves being refiected from vertical or nearly vertical wells. In smaliescele models involving wave action the side walls and wave generstor of the mode’s or tanks may result in reflections which can produce erroneous or misleading resuitse Total reflection will occur at smooth vertical, rigid, impermeable barriers, while for almest total dissipation a flat sloped permeable wall is necessarye There is a transi= tion region between total reflection and total dissipation. Besides the slope of the wall and the characteristics of its construction (rigidity, permeability, roughness of the surface ete.) the following factors effect the dissipation of wave energy: (i) the water depth, (ii) the weve length, (iii) the wave height, (iv) the angle of wave approach. Runs il and 12 (Fige 3b) were made to demonstrate the reflection of gravity water waves at a rigid, vertical-walled barrier. In Run 1] a barrier was introduce at 45° to the direction of wave approach, while in Run 12 a quarter of a cylinder was used with the tip of the wedge facing the approaching waves and the sides of the wedge inclined by 45° to this direction. The depth of the water was uniform for both of the runse From the few experiments performed it appears that (i) the angle of incidence was equal to the angle of reflections (ii) the wave lengths and velocities remain unchanged - only the direction of travel being changed; (iii) in case of a smooth, rigid impermeable vertical wall, the individual wave heights were not greatly affected by the reflection. Conclusions (i) and (ii) are verified by the fact that the incident waves and reflected waves formed almost perfect squares when the angle of incidence was 45°, as can be readily seen in the photographs of both Run 11 and Run 12 (Figure 3b)e The third conclusion came from the fact that the intensity of white crest= lines of reflected waves close to the obstacle was almost the same as the intensity of the incident waves (see Run 11). Runs 15 to 25 (Figures 3f and 3g) also show reflection patterns, where the pattern of reflected waves appear to be circular. Total reflection may result in doubled wave heights due to the superposition of incident and reflected wavese This is demonstrated in Run 11 (Figure 3b) by the high intensity of the intersections of incident and reflected wave trains. An engineer, designing a harbor should take this fact under consideration. Breakwaters to be built close to navigation channels should be constructed so as to absorb all or most of the wave energy without considerable reflection. There are many harbors where this faot was not taken into consideration; the result being that the entrances to the harbors are dangerous to navigation, even for incident waves of medium heights Islands When 2 train of waves is interrupted by an island, there is generally a zone of “wave shadow" in the lee of the island. Since the regular pattern of a long swell is disturbed even at great distances beyond islands, the early navigators were able to use this phenomenon as a guide to new islands. The factors which ,) influence the penetration of wave energy into the wave lees of am isléiud sres £1) refraction by underwater topography, (ii) refraction by currents, (iii) diffraction, (iv) variability in direction of wave travel. These factors may be closely related. Refraction by underwater topography. The distribution of refracted wave energy in the lee of an island is critically dependent upon the bottom slope. When the wave approaches the shore, its velocity will be reduced due to the decreas- ing depth of the water; and when the crests reach the beach they tend to become parallel to the shoreline, regardicss of their direction of approach from deep water. The waves "wheel" around and break nearly at right angles to the beach. In Run 13 (Figure 3c) a transparent cone-shaped island was introduced, with uniformly sloping beaches extending above the water level. The slope of the beach was 1:15 (see data in Table I). One can see clearly the refraction of the waves on the beach: the widening of the crest-lines in the pictures indicates the increase in wave heights toward the shore due to the convergence of energy along the crest. Refraction by currents. The wave eharacteristics such as steepness, length and @irection of travel will be changed when waves encounter currents. (i) The steepnesses of waves meeting opposing currents increases, and when the current is strong enough the waves might break. (ii) The wave steepnesses will be reduced by a current in direction of the wave travel. (iii) When waves meet a current at an angle, directional changes occur in wave travel. In these idealized ripple-tank studies no currents were present. The usual semi-permanent currents around islands is not significant because of low current velocities involved. However, tidal currents around the islands may be strong enough to cause important refraction effects. Diffraction of waves around the islands. Wave energy is also propagated into the lee of an island by diffraction, as well as by refraction. The effect of such diffraction was estimated by Putmam and Arthur (Ref. 2). They utilized the theory of diffraction of waves by a semisinfinite plane barrier in water of uniform depth as introduced by Penny and Price (Ref. 9). This theory does not apply for small islands, but the results appear to be useful in the case of large islands (many wave lengths in diameter). This is illustrated by compar- ing the results of runs 15 to 25 (Figs. 3f and 3g) where a wave-train is interrupted by a cylinder with the axes perpendicular to the water surface and with the cylinder diameter varying from 0.09 L to 6.5 L. It appears that very small cylinders have almost no effect upon the wave train (Run 15, D = 0.09 L). For the cylinders with D = 0.8 L the effect of the cylinder was apparent to a distance aff approximately 3 wave lengths in the lee of the cylinder. This distance increased with increasing cylinder diameter, until at D = 3.1L (Run 23, Figure 3g) nearly circu}ar waves passed around the cylinder without interference effects in the lee. This phenomenon takes a relatively definite configuration at a distance of approximately D = 6 L. Hence, it appears that the theory of diffraction of waves around a semi-infinite breakwater tip might be used for islands larger than 6 wave lengths (which compared with diffraction at a breakwater gap). However, more experiments are necessary before more definite conclusions can be stated. Variability in direction of wave travel. The extent of the sheltered region in the lee of an island depends largely upon the variability in direction of travel of the incident waves. Larger variability means an increase in wave intensity in the sheltered area. 10 References Robert S. Arthur - “The effect of islands on surface waves”, Univ. of Calif. Press, Berkeley, 1951 J. Ae Putnam and Robert S. Arthur - “Diffraction 6f water waves by breakwaters", Am. Geophys. Union Trans., vole 29, ppe 481-490 Je W. Johnson = “Engineering aspects of diffraction and refraction", Proceedings, ASCE, March 1952 A. J. Chinn - “Effect of surface tension on wave velocity on shallow water", Univ. of Calif. Report No. HE-116-302 F. Le Blue, Jr. and JeW. Johnson = “Diffraction of water waves passing through a breakwater gap" = Transactions, Am. Geophys. Union, vol. 30, 1949 J. We Johnson - “Generalized wave diagrams”, Second Conference on Coastal Engineering, Houston, Texe, Nov. 1951. H. Je Shoemaker and J. The Thijsse - “Investigation of the reflection of waves", third meeting - Troisieme Reunion Grenoble Isere, 5, 6 et 7 Sept. 1949. Beach Erosion Board - “Reflection of solitary waves", Technical Memorandum No. 11 Penny and Price - "Diffraction of sea waves by breakwaters", Directorate, Misoellaneous Weapons Development Technical History 26, Artificial Harbors, Sec. 3D. Jo He Carr and M, E. Stelzriede - “Symposium on Gravity Waves", National Bureau of Standards, Washington D.C., June 1951 Robert L. Wiegel - "Tables of the functions of a/L and q/L» Unive of Calif. Robert HB-116=-265, January 30, 1948 Wave generator FIGURE | - GENERAL VIEW OF EQUIPMENT Wy _LNAWdINOS SHL 3G HOLSNS - @ AYNDSIS = ee FIYNOS INIOd ee ee ee | YNYL JO WOLLOG FN -—SSV19 FLV Td —— YIINA TAO SILLS ZL LSE Lec t i FOLVHINFIP JAVA NAF HS MINS ss ae SIHP FAVA as WOH SINT LHOIKG 13 1.0 0.5 0 1.0 F1 RUNG For data see Table I FIGURE 3a 14 15 FIGURE 3b on ea CO re re *° ae Sibu i aeeca t ay RUN 13 Photos a to k taken at intervals of 0.25 second FIGURE 3c 16 RUN 13 (cont.) aty| FIGURE 3d RUN 13. (cont.) Photos | to r taken at an interval of 0.02 second 18 FIGURE 3e RUN I3r RUN 15 ay FIGURE 3f FIGURE 39 PROGRESS REPORTS ON RESEARCH SPONSORED BY THE BEACH EROSION BOARD Abstracts from progress reports on several research contracts in force between universities or other institutions and the Beach Erosion Board, together with brief statements as to the status of research projects being prosecuted in the laboratory of the Beach Erosion Board, are presented as follows? Ie University of California, Contract No. DA-l9-055-eng-8. A. Status Report No. 11 - 1 Aug through 30 Sept 1953 Work completed in current period - During August an intensive field survey of the movement of sand off rocky promontories in Southern California was made. The work was carried on with 2 DUKWs and a field party of nine mene In the course of this survey, 5 profiles were run off Point Dume, 9 off Point Conception and 5 off Point Arguello. Approximately 250 bottom samples were collected along these profiles from water 8 to 80 feet in depth. The field examination of these samples indicated that the sand along these profiles was essentially of the same size as that found on adjacent pocket beaches and along the coast at Santa Barbara, thus indicating clearly the opportunity for sand to move around these points. Rocky bottom was encountered on only two profiles, one at Point Gonception and the other at Point Arguello. Statistical analyses of the samples collected at Santa Barbara in the course of the drilling program last March have now been completed and a series of graphs summarizing the salient points of the investigation are in the process of construction. Work contemplated during October and November - The samples collected during the recent field survey are now in the process of analysis and during October and November mechanical, mineralogical and other types of analyses will be made and the data will be compiled in a form suitable for proper interpretation. Be Status ieport No. 12 - 1 Oct through 30 Nov 1953 Work completed in current period - This period has been devoted tothe preparation of areport on the results of the bore-holes drilled at Smta Barbara last spring. As of 30 November, this report is 95 percent completed, and it is scheduled to be in the hands of the Beach Erosion Board around the first of the year. 21 This work has showns (1) The sediments in the filled area west of the breakwater are definitely more coarse grained than in the Feeder Beach area to the east where wave action presumably is gentler. (2} The grain size as well as the coefficient of sorting increase as the berm is built up. (3) The sprain size increases as the berm is built seaward into more exposed positions. Work contemplated during December and January - The report on results of the hore-hole studies at Santa Barbara will be completed and the mechanical analysis of the samples collected last summer off Point Arguello, Point Conception and Point Dume will be run. il. University of California, Contract Noe pA-9-055-eng-17, Status Report No. 2 - 10 June 1953 to 1 October 1953. During this period the report "Stability of Oscillatory Laminar Flow Along a Wall" was completed and distributed, This report deals with a set of experiments which were made with an oscillating bed with various rough- nesses; and the conditions at which flow changed from laminar to turbulent were determined. (This report will be published in 195) as a Technical Memorandum of the Beach Erosion Board). lxperimental work with a movable bed was completed and a rough draft of a report started. This report deals with the mechanics of sand move- ment on sandy beds in relatively deep water, due to the action of oscillatory waves of small amplitude and long wave length. On the assumption that the bottom water oscillations are nearly simple harmonic motions, sand movement mechanics were studied by oscillating a section of the bed horizontally through still water. Only that part of the sediment load which rolls or creeps along the bottom, as distinguished from suspended load which is carried in the fluid in suspension, is considered in this report. Its initial and general movement, the critical velocities and horizontal amplitudes re- quired for such movements, the conditions of flow at the interface - whether laminar or turbulent, are experimentally measured and analyzed theoretically, for grains of various sizes and densities. Further experimental work with glass beads of different sizes has been started and will be incorporated in the above report at a later date. IIEIES University of California, Contract No. DA=)9=055-eng=31, Status Report No. 1 - 2 Aug 1953 through 31 October 1953. This research investigation is designed to study the fundamental mechanics of the formation and growth of wind waves and wind tides in shallow water. An inclosed wave flume equipped with a suitable blower is the basic piece of equipment being used for the study. The Beach Brosion Board and the Jacksonville District, Corps of Engineers, are joint sponsors of this contract. The laboratory flume used in this study was constructed at University expense prior to the date at which work on the contract was permitted (2 August 1953). Most of the work during the first two months was devoted to install- ing instruments for measuring waves, wind, pressure drop, and wind tide. Tests to date have been concerned with the calibration of instruments and preliminary runs with smooth walls. Some study also has been given to the type of roughness that might be used to give an ultra-rough bed in sub- sequent tests. Iv. Analyses of orbital velocity data show that the observed horizontal orbital velocities compare favorably with velocities predicted from solitary wave theory when: 1) thewave profile is not complex , and (2) the relative wave height H/h is greater than about 0.4. The agreement with wave theory is somewhat better for long period waves than for short period waves, but in general is still quite good for wave groups with significant periods as short as about 6 seconds. Seven months of observing reference rods by divers using self-contained diving gear have shown rapid and extensive changes in shallow water (6 ft.), with much less change of sand level in greater depths (30 to 70 ft.). A new series of reference rods was placed, during September, at 20-ft. intervals along a profile extending through the surf zone and onto the beach foreshore. The purpose is to obtain accurate measurements through the surf zone. Because of the important role ripples play in the mechanics of sand transport by wave action, a systematic program of measurement and ripple study has been initiated. Ripples are photographed and measured in con- junction with the reference rod studies. Ripples have always been found to be present when the significant orbital velocities exceed approximately 0.3 ft./sec. (for sand with a median diameter of about 0.12 mm.). In general, the type of ripple is related to the nature of the orbital dis- placement and velocity. The form of the ripple profile tends to imitate in miniature the form of the profile of the generating surface wave above it. In deep water, where the wave profile is trochoidal, the ripple is tro- choidal; in shallow water, where wave forms are solitary, ripples consist of isolated crests separated by flat troughs. further studies are planned; and understanding of the mechanism of sand movement in relation to ripple regime may aid in explaining some of the apparent anomalies between sand transport and the rigor of wave action. 23 The and Colle texas, | Lontract No. vending 31 Oct 1953. hanic al Agricul tural Ig Meld Operations. field operations were continued from July 21, 1953 through this quarter at the Pure Oil Structures A and B. The third recorder was installed recently at the end of Sun Oil Pier. Wave records were obtained for 20 minute intervals once every 6 hours at all sites during operation. Field Operations have temporarily been curtailed at the Pure (il otructures, and are being resumed at the Sun Oi] Pier. It is felt that for the time being, efforts should be made to get some comprehensive wave data at the Sun Qi] Pier before resuming operations at the Pure Oi] Structure. in addition funds are running low for transportation and boat rental (the cost of which is greater) for operations at the Pure Oi] sites. Analysis had begun of the wave records obtained at the Pure Oil Structures A and B during this quarter. 2. ‘theoretical Investigations. Work has continued on the theoretical. investigation of the effect of bottom fluctuations on the change in wave height, Computations involving the combinations of wave generation andw ave energy Joss due to bottom friction has been continued. Relatiunships for the steady state conditions of wave generation over a flat bottom have been developed. That is, dimensionless relationships of et /U2 and gT/U versus gd/US have been developed for unlimited fetch length and unlimited wind duration and for bottom friction factors of .01 and .06. The Lake Okeechobee wave data as wel] as the wind wave data obtained in the Atchafalaya Bay during the fall of 1952, seem to fit the above relationships best for a bottom friction factor of .O or 02. 30 Technical Papers and Reports. Work has progressed slowly on the technical report "Change in Wave Height Due to Bottom t‘riction, Percolation and Refraction". The reason for the slow down is that most of the time had been spent completing another technical report "Surface Waves and Offshore Structures; the Design Wave in Deép or Shallow water, Storm Tide, and Yorces on Vertical Piling and Large Submerged Objects", by KR. O. Reid one Ge Le Bretschneider. A third technical report, “Wave Energy Loss of Wind Generated Waves Over a Shallow Bottom" has been initiated. This report summarizes the analytical rela tionships Se uaaanes for shallow water wind wave generations, as well as the results of the analysis of the wind wave records obtained in the shallow water of the Atchafalaya Bay. A fourta technical report has been initiated on the effect of bottom fluctuations on wave heights. ine) 4 VI. Massachusetts Institute of Technology, Contract No. VA-l9-055- eng-16, Progress Report dated 15 December 1953. The wave generator is completed, has been tested over its entire range and has been found satisfactory in all respects. Observations of the location of the breaking point of the waves on the 1:15 beach have shown a shifting of the breaking points due to secondary wave reflections in the channel, over a sizable cistance. A wave filter of expanded aluminum has been constructed and installed to prevent the condition outlined above.. It has been tried and found to perform satisfactorily. A wave profile recorder based on the variable capacitence type has been developed and constructed for this as well as another related project. This recorder has been tested and performs very well, however, delay in the delivery of the recording equipment has prevented the start of the test program proper. WAEIL g Waterways Experiment Station, Vicksburg, Mississippi, Progress Report for Period ending 30 November 1953. Wave Run-up on Shore Structures - Overtopping and run-up tests on a smooth faced pavement with a sea side slope of 1 on 14 and a beach slope of 1 on 10 were completed. ‘Similar tests on a step-faced seawall with sea- side slope of 1 on 1$ were initiated. Effects of Inlets on Adjacent Beaches - Test was continued through tidal cycle 50, and the results are now being studied to determine whether the test has been carried to its practical end, or whether additional operation would result in added information. WAEIEIE Report Beach #rosion Board, liesearch Division Status for Quarter ending 15 December 1953. Project In addition to the research projects under contract to various institutions which are reported on above, the Hesearch Division of the Beach Erosion Board is carrying out certain projects with its own facilities. The main un- classified projects have been described in previous numbers of the Bulletin, and a short description of some of the work accomplished through the last : quarter is given below. Statistical Wave Data for the North Atlantic Coast - Tabulation of three years of data for four stations along the North Atlantic coast of the U. S. has been comple ted, and a report similar to those issued for the Great Lales is: scheduled to be published early in 195]. A comparison of 25 the hindcast values with those recorded at Long Branch, New Jersey has been made by applying a refraction analysis to the deep water hindcast data, and the agreement is quite adequate. tudy of Methods of Sand Ana Settling Tube - The Visual Accumulation Tube has been received from the St. Paul District and erected; tests will be undertaken to determine its adaptability to the needs of the Board for the size analysis of beach sands. Analysis of Moving Fetches for Wave Forecasting = A report on the methods of forecasting waves from moving fetches has been completed and is scheduled to be published early in 195). Project ESMOND = The laboratory testing for this project is complete and a report is being prepared. The results generally indicate that, of all the sounding lead shapes tested, a spherical shape offers the best possibilities for an improved sounding lead in soft sediments. Study of Effect of Tsunamis = The draft of the preliminary report is completed and under review. The tests described previously have in- dicated that relative run-up (R/H, where R is the maximum vertical rise and H is the wave height at the toe of the slope) increases with a decrease in wave steepness (H/L where L for these tests is defined as the horizontal distance from the first noticeable rise of water above the still water level to the point of maximum wave crest height). Tests are being con- tinued to relate the wave height H as measured above to the wave height at the shore line. Routime progress, testing, and analysis has been made on the other projects being carried out by the Research Division. A project report by G. M. Watts "A Syudy of Sand Movement at South Lake Worth Inlet, Florida" was published as Technical Memorandum No. 34, and papers on "Hindcast Wave Statistics for the Great Lakes," "Field Investigations of Suspended Sediments in the Surf Zone," and "Pressure of Breaking Waves on Vertical Structures" were prepared and presented by T. Saville, Jr., G. M. Watts, and C,. W. Hoss respectively at the Fourth Conference on Coastal Engineering; these papers will be published in The Proceedings of this meeting. fo Cy SE RATT PDRETAM amiInT we BEACH EROSION STUDIES Beach erosion control studies of specific localities are usually made by the Corps of Engineers in cooperation with appropriate agencies of the various States by authority of Section 2 of the River and Harbor Act approved 3 July 1930. By executive ruling the costs of these studies are divided equally between the United States and the cooperating agencies. Information concerning the initiation of a cooperative study may be obtained from any District or Division Engineer of the Corps of Engineers. After a report on a cooperative study has been transmitted to Congress, a summary thereof is included in the next issue of this bulletin. A summary of reports transmitted to Congress since the last issue of the Bulletin and a list of authorized cooperative studies follow: SUMMARIES OF REPORTS TRANSMITTED TO CONGRESS GULF SHORE OF GALVESTON ISLAND, TEXAS The area studied is located on the Gulf shore of Galveston Island, Texas, about 345 miles west of the mouth of the Mississippi River. It ex- tends southwest from the south jetty at the entrance to Galveston Harbor a Gistance of 11.5 miles. Galveston Island is a low barrier beach island of fine sand about 28 miles long and varying in width from 1/2 to 3 miles. The natural surface of the island has a general elevation of h to 5 feet above mean sea level. Dunes along the Gulf shore have top elevations up to 12 feet above sea level. The foreshore and offshore bottom are gently sloping. Galveston is a summer resort community and an important Gulf port. The population of the island is estimated at 80,000. In addition, it is estimated that there are as many as 750,000 summer visitors. The mean tidal range in the Gulf at Galveston is 1.3 feet. Tidal heights are greatly influenced by winds and storms, the maximum tidal height of record being 14.5 feet above mean sea level. Tidés over 3 feet in height however are relatively rare, having occurred on the average about once in 2 years. with light winds and normal tides, waves just offshore in the study area probably do not exceed 2 feet in height. Available data indicate that during hurricanes with accompanying high tides, wave crests have reached elevations of about 20 feet above mean sea level. Swells from the east occurring 10 percent of the time, are refracted to approach normal to the shore between the jetty and the center of the groin area, but west of that point they have a westward component. Swells from the south occur 8 percent of the time and have an eastward component. In its natural state the shore of the study area was subject to erosion, at least in the portion adjacent to the inlet to Galveston Bay. Following construction of the Galveston south jetty from 1887 to 1897, extensive accretion occurred in the section for about 3.6 miles southwest of the jetty. 27 now known as East Beach. At the time of the study this accretion was still active, although at a lower rate. A portion of the study area southwest of the jetty has been protected by a massive concrete sea wall and embankment 6.7 miles in length, extending to a point 7./) miles southwest of the jetty. The wall was constructed partly by local interests and partly by the United States. A groin system compris— ing 13 steel sheet pile groins was built by the United States between 1936 and 1939 along the westerly 3.6 miles of the wall. This groin system has been effective in protecting the base of the sea wall by accumulating beach material at a slow rate, but the increase in beach width above sea level has been small. The slow rate of accumulation results in part from heavy losses during hurricanes. The remaining h.1 miles of the study area, known as West Beach, have no protective measures, but a Federal project has been authorized for ex- tension of the sea wall 16,300 feet southwestward. Recent surveys indicated that the easterly half of this reach has been eroding slowly while the westerly half has been building up. The loss over the easterly 2.2 miles averaged 3,200 cubic yards annually from 1946 to 1949. Experience indicates that, due to additional losses during hurricanes, the additional average annual volume of material required to stabilize this reach would be about 80,000 cubic yards. The district and division engineers and the Beach Erosion Board con- curred in the finding that only a portion of the study area in front of the proposed sea wall extension required remedial measures, and that the most practical and economical plan for maintenance of this beach is by artificial replacement of beach materials where and when lost by erosion at an estimated average annual cost of $24,000. As there is no Federa) property in the area and existing law includes no policy for Federal participation in maintenance costs of other property, no Federal project for maintenance of the Gulf shore of Galveston Island was recommended. In compliance with existing statutory requirements, the Beach Erosion Board stated its opinion thats a. it is not advisable for the United States to adopt a pro- ject for protection of the shore of the study area at this time; b. No improvement of the beach is required, but public interests in maintenance thereof is associated with ownership of a small proportion of the shore frontage, public recreational benefits and reduction in maintenance costs of the sea wall; and c. No share of the expense should be borne by the United States. The Chief of Engineers concurred in the views and recommendations of the Beach Erosion Board. 28 STATE OF CONNECTICUT - HOUSATONIC RIVER TO ASH CREEK The area studied comprises the shore of Long Island Sound between the mouth of Housatonic River and the mouth of Ash Creek. It includes the shores of the Town of Stratford and the City of Bridgeport, a total length of about 12 miles. Bridgeport, at the west end of this shore area, is about 50 miles east of New York City. The shore area is extensively developed for residential use. The permanent population of Stratford and Bridgeport totals about 192,000. There is a minor increase in the population of Stratford in the summer. In Stratford there are two small town-owned beaches used for recreational purposes, in addition to some town-owned frontage which is leased for private residential use. In Bridgeport, the city owns Pleasure Beach and Seaside Parks which are used for recreational purposes. it also owns the headland shore of Grover Hill, which is not used. Long Island Sound is a tidal arm of the Atlantic Ocean. Tides are semi-diurnal, the mean range at Bridgeport being about 6.8 feet. The spring range is about 8 feet. The maximum tide of record at Bridgeport was 7 feet above mean high water. Tides 3 feet or more above mean high water occur about once a year. With a tidal stage of 3 feet above mean high water, the maximum height of breakers landward of the low water line is about 8 feet. Larger waves can reach the shore only during infrequent higher tides. Ocean swells entering Long Island Sound between Race Point and Little Gull Island may affect littoral processes, but the waves of primary importance are those generated in the Sound. Ordinary short storm waves cause littoral movement and offshore loss of beach material. The influence of swells is probably insufficient to cause appreciable revurn of material from offshore by wave action. Storm waves which cause the greatest move- ment of beach material are those from the east and southeast. The pre= dominant direction of littoral drift is north along shores aligned generally north and south, and west along shores aligned generally east and west. The study area is characterized by headlads of unconsolidated glacial material, from which wave-built bars or spits have been formed and the landward areas generally have filled and become marshy. The headlands formerly supplied ample material to the intervening beaches, but, except east of Foint No Point, the headlands are now generally protected by seawalls and revetments. The supply of material has thus been reduced or eliminated, and consequently the beaches have slowly deteriorated. Groins have been found to be capable of causing minor accretion areas and Stabilizing a narrow band along the upper portion of the beach, but the natural supply of material is insufficient forthe formation of adequate protective beaches by groins alone. The building and maintenance of adequate beaches may be accomplished by artificial placement of sand. The rate of loss of fill can be reduced by groins. The division engineer concluded that practicable plans which merit consideration for the protection and improvement of beaches within the study area are as follows: 29 ae Short Beach - Direct placement of sand fill along the shore now used for public bathing and north thereof in front of existing cottages which closely border the shore; b. Point No. Point to Long Beach - Direct placement of sand fill in front of cottages which closely border the shore adjacent to Eong Beach and construction of impermeable groinss; c. Long Beach (The Breach) - Construction of a riprap dike across the breach or direct placement of sand fill to restore the bar; d. Long Beach (West of Breach) - Direct placement of sand fill in front of cottages which closely border the shore and construction of impermeable groins; e. Seaside Park - Direct placement of sand fill along the shore west of Breezy Point. The division engineer and Beach Erosion Board recommended adoption of projects by the United States authorizing Federal participation subject to certain conditions by the contribution of Federal funds in an amount equal to one-third of the first cost of restoring the beach at Short Beach, Stratford and of widening 8,800 feet of beach at Seaside Park, Bridgeport both to a width of 125 feet by direct placement of sand. In accordance with existing statutory requirements the Board stated its opinion thats a. it is advisable for the United States to adopt projects authorizing Federal participation in the cost of restoring Short Beach and of protecting and improving the shore of Seaside Park west of Breezy Point; b. The public interest involved in the proposed measures for Short Beach and Seaside Park is associated with prevention of damages to publicly owed property and recreational benefits to the public; and, e. The share of the expense which should be borne by the United States is one=third of the first cost of the work. The amount of this share is currently estimated at $2,150 for Short Beach and $105,800 for Seaside Park. The Chief of Engineers concurred in the views and recommendations of the Beach Erosion Board. The purposes of this study were to: a, Review master plans of shore line improvement as prepared by the County of Eos Angeles and cities therein, within the area of this study, in order to comment on the engineering feasibility of these plans with respect to the recreational beach area, and to determine the most suitable means of providing stability to the shore line; b. Determine the effect of existing structures within this area upon the shore line, particularly Santa Monica, Venice, and Redondo breakwaters ,and recommend the most suitable remedial measures where the necessity for such measures is indicated; c. Determine the effect of proposed shore line improvements on existing flood control outlet works in the area under investigation; de Make such studies and economic analyses as may be necessary to determine the maximum extent of Federal aid for which the local interests may be qualified under Public Law 727, 79th Congress. The study area comprised the Pacific Ocean shore line of California from Point Mugu to San Pedro Breakwater, a length of 68 miles. This stretch of shore lies in Ventura and Los Angeles Counties. The principal communities along this shore are Santa Monica, kl Segundo, Manhattan Beach, Hermosa Beach and Redondo Beach. All are located on the Santa Monica Bay shore in Los Angeles County. The population of Ventura and Los Angeles Counties exceeds 11,000,000. Seasonal variations in the population are unimportant. The shore frontage of Ventura County is privately owned. Of the approximately 61 miles of shore in Los Angeles County, only 20 miles of the section between Topanga Canyon and San Pedro Breakwater are included in the desired plan of improvement. Of these 20 miles, 86 percent are publicly owned. Local interests intend to obtain other lands required for the proper functioning of the beach improvements. The terrain adjacent to the shore suggested division of the study area into three major subdivisions as follows: a. Point Mugu to Santa Monica Canyon - This portion of the study area comprised about 36 miles of generally rugged shore extending in a general east-west direction along the foot of the Santa Monica Mountains. The coastal area is drained by a number of short, steep, intermittent streams which contribute sand and gravel to the shore during winter floods. The coast highway generally parallels the shore but is separated from it by sea cliffs. Relatively narrow beaches generally lie at the foot of the cliffs. The largest beaches are Zuma Beach lying west of the Point Dume projection and Malibu Beach, the delta at the mouth of Malibu Creek, The BE shore area is relatively little developed except at its eastern extremity and at the private Malibu Beach Colony. Zuma Beach, owned by the State, is being developed for operation as a County park. Offshore the narrow continental shelf is dissected by Dume Canyon. Most of the shore of this area has been reasonably stable during historic time. be Santa Monica Canyon to Malaga Gove + This portion of the coast comprised about 16 miles of the shore of Senta Monica Bay gently curving from a northwest-southeast direction at the upcoast end to a nath-south direction at the Malaga Cove end. The coastal plain is generally a plateau elevated considerably above sea level and terminating generally at the shore in bluffs of alluvial material. The principal drainage is by Ballona Creek through a valley about 2 miles wide at the shore, which is separated from the ocean by a barrier beach, except for a narrow flood channel pro- tected by jetties. South of Ballona Creek the bluff is a dune formation known as the El Segundo Sand Hills. The coastal drainage contributes little or no beach material to the shore. In its natural state the beaches in this section were relatively wide and uniform. Offshore the continental shelf slopes uniformly seaward to a depth of 50 fathoms over a distance from shore of 6 to 10 miles, beyond which the ocean floor slopes steeply to interisland basins 500 to 1,000 fathoms deep. The Redondo Canyon cuts deeply into the continental shelf, the 50-fathom contour approaching to a point about 3,000 feet off Redondo Beach. An offshore breakwater at Santa Monica and an attached curved breakwater forming Redondo Beach Harbor are the principal structures affecting the shore line. Each has interrupted downcoast littoral drift causing accretion on the upcoast side and erosion downcoast. Other structures affecting the shore less acutely are the Venice breakwater, Ballona Creek Jetties, the El Segundo groin and the large piling clusters of piers. Beaches between the Santa Monica breakwater and El Segundo were restored or widened by artificial deposit of sand on several occasions, the principal one being the placement of about 14,000,000 cubic yards of sand in 197-8. Beaches in the section are at present in relatively good condition except for a short stretch south of Redondo Beach Harbor where no beach exists in front of the stone seawall, but no protective measures have been provided to stabilize the restored beaches, The coastal area is extensively developed for residential and recreational use. An oil field is being exploited on the barrier beach and low inland area at Ballona Creek. A number of city and county public beaches are operated in this section. ce Palos Verdes Hills - Malaga Cove to San Pedro Breakwater - This portion comprised the remaining 16 miles of the study area. The shore line is rugged and rocky with cliffs 100 to 300 feet high. A few sandy beaches exist between the rocky prominences. Because of its inaccessibility the immediate shore area is almost undeveloped. The high inland areas are used for residential and agricultural purposes. Offshore, the continental shelf is comparatively narrow, the 50-fathom contour lying from about 1 to miles from the shore. At the root of the San Pedro Breakwater at the south limit of the study area, Cabrillo Beach has been developed by the city of Los Angeles. The beach itself was built almost entirely by the artificial deposit Be of 2,800,000 cubic yards of material dredged from Los Angeles Outer Harbor. Adequate access and public park facilities have also been provided. The artificial beach is in good condition, but is subject to rapid erosion. Los Angeles County has adopted a master plan of shore line development for recreational purposes which includes, among other things, widening the beaches from Topanga Canyon to Ballona Creek, a maximum of 1,200 feet and from El Segundo to Malaga Cove to widths of 300 to 450 feet. The plan proposed groin systems to stabilize the widened beaches and also a groin at Cabrillo Beach to stabilize the beach already widened at that location. Other incidental work included in the plan comprised extension of existing storm drains and removal of the Santa Monica Breakwater. Navigation improve- ments at Playa del Rey and Redondo Beach Harbor, also included in the master plan, were considered by the Corps of Engineers in previous reports and so were omitted from the present report except for necessary overlapping details. The district engineer with concurrence of the division engineer and Beach Erosion Board developed a modified plan for protecting the shores of Los Angeles County. They concluded that since the shore to be improved was or will be publicly owned and public interest in the improvements is 100 percent, Federal participation to the extent of one-third of the total cost of the protective features, in accordance with the policy established by Public Law 727, 79th Congress, is warranted. They recommended adoption of a Federal project for reimbursement subject to certain conditions, to local interests of an amount equivalent to one-third of the cost of the protective features of the following modified master plan of shore line development: widen the existing beaches to approximately 1,000 feet between Topanga Canyon md Ballona Creek (seaward 200 feet considered a protective feature), and to approximately 300 feet between El Segundo and Malaga Cove (seaward 150 feet considered a protective feature), except between the Redondo Beach breakwater and a barrier groin to be constructed near Topaz Street in Redondo Beach; construct nine groins between Topanga Canyon and Temescal Canyon; construct five groins between Temescal Ganyon and the proposed entrance to Playa del Rey Harbor (to be deferred pending demonstra- tion of need); extend seven storm-drain structures through the widened beach (that part extending through the protective beach considered a protective feature); acquire and rehabilitate the Santa Monica breakwater; construct a barrier groin in the vicinity of Topaz Street in Redondo Beach (to be deferred pending demonstration of need) ¢ and construct a barrier groin at Cabrillo Beach; all at an estimated total first cost of 49,488,000 for the protective features, of which the Federal Government would reimburse local interests in an amount estimated at $3,163,000. In accordance with existing staturory requirements, the Beach HLrosion Board stated its opinion that: a. it is advisable for the United States to adopt a project authorizing Federal participation in the cost of protecting the proposed 33 improved shore of Los Angdles County between Topanga Canyon and Malaga Cove and at Cabrillo Beach; b. The entire interest involved in the proposed measures will be public. It is associated with prevention of losses of public property, savings in automobile travel and recreational benefits to the general public; c. The share of the expense which should be borne by the United States is one-third of the first cost of the recommended protective features of the master plan, modified as recommended by the district engineer. ‘The Federal share is estimated at $3,163,000. The Chief of Ingineers concurred generally in the views and recommenda- tions of the Beach Brosion Board except for the extent of Federal participa- tion under Public Law 227, 79th Congress. in interpreting that law, it appeared more likely to him that Congress intended that it should apply to protection of existing shore lines, rather than proposed shore lines in some artificially advanced position. He noted that protection of the advanced shore line would be more costly than protection of the existing shore, and therefore, if Federal participation were provided to the extent of one-third of the cost of protection of the former, it would result in greater Federal assistance than was probably intended by Congress when it passed Public Law 727. Consequently, in the absence of more specific expression of the intention of Congress, the Chief of Engineers believed that the Federal participation should be limited to one-third of the cost of protecting the existing shore line. On this basis the Federal contri-~ bution is estimated at $3,099,000. AUTHORIZED COOPERATIVE BEACH EROSION STUDIES MASSACHUSETTS PEMBERTON POINT TO GURNET POINT. Cooperating Agency: Department of Public Works. Problem: To determine the best methods of shore protection, prevention of further erosion and improvement of beaches, and specifical- ly to develop plans for protection of Crescent Beach, the Ce Glades, North Scituate Beach and Brant Rock. CONNECTICUT STATE OF CONNECTICUT. Cooperating Agency: State of Connecticut (Acting through the Flood Control and Water Policy Commission) Problems To determine the most suitable methods of stabilizing and improving the shore line, Sections of the coast are being studied in order of priority as requested by the cooperating agency until the entire coast has been included. NEW_YORK N. Y. STATE PARKS ON EAKE ONTARIO. Cooperating Agency: Department of Gon- servation, Division of Parks. Problems To determine the best method of providing and maintaining certain beach and preventing further erosion of the shore at Fair Haven Beach and Hamlin Beach State Parks, and the Braddock Bay area owned by the State of New York. NEW JERSEY STATE OF NEW JERSEY. Cooperating Agency: Department of Conservation and Economic Development. Problem: To determine the best method of preventing further erosion and stabilizing and restoring the beaches, to recommend remedial measures, and to formulate a comprehensive plan for beach preservation or coastal protection. NORTH CAROLINA CAROLINA BEACH. Cooperating Agency: Town of Carolina Beach Problem: To determine the best method of preventing erosion of the beach. ALABAMA PERDIDO PASS AND ALABAMA POINT. Cooperating Agency: Alabama State High- way Department. Problem: To determine the best method of preventing further erosion of Alabama Point, for stabilizing the inlet, and for determin- ing the extent of Federal aid, if any, in the cost of such proposed plans for protection and improvement as may be recommended. LOUISIANA SHAND ISLE. Cooperating Agency: Department of Public Works, “tate of Louisiana. Problem: To determine the best methods of preventing further erosion of the beaches along the Gulf shore of Grand Isle. CALIFORNIA STATE OF CALIFORNIA. Cooperating Agency: Division of Beaches and Parks, State of California. Problems To conduct a study of the problems of beach erosion and shore protection along the entire coast of California. The current studies oover the Santa Cruz and San Diego areas. WISCONSIN KENOSHA. Cooperating Agency; City of Kenosha. Problem: To determine the best method of shore protection and beach erosion control. MANITOWOC-TWO KIVERS. Cooperating Agencies: Wisconsin State Highway Commission, Cities of Manitowoc and Two Rivers. Problem: To determine the best method of shore protection and erosion control. TERRITORY OF HAWAIL WAIMEA & HANAPEPE, KAUAI. Cooperating Agency: Board of Harbor Commissioners, Territory of Hawaii. Problems To determine the most suitable method of preventing erosion, and of increasing the usable recreational beach area, and to determine the extent of Federal aid in effecting the desired improvement. 36