WS, el Bug. KeaGh. lech, Key Fete CERCTO 7S Sp (740 TECHNICAL REPORT CERC-90-15 US Army Corps of Engineers | FUNCTIONAL DESIGN OF BREAKWATERS FOR SHORE PROTECTION: EMPIRICAL METHODS by Julie Dean Rosati Coastal Engineering Research Center DEPARTMENT OF THE ARMY Waterways Experiment Station, Corps of Engineers 3909 Halls Ferry Road, Vicksburg, Mississippi 39180-6199 ee “DOCUMENT LIBRARY Woods Hole Oceanographic Institution September 1990 Final Report Approved For Public Release; Distribution Unlimited Prepared for DEPARTMENT OF THE ARMY US Army Corps of Engineers Washington, DC 20314-1000 Under Civil Works Research Work Unit 32535 Destroy this report when no longer needed. Do not return it to the originator. 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. The contents of this report are not to be used for advertising, publication, or promotional purposes. 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SUBJECT TERMS (Continue on reverse if necessary and identify by block number) GROUP SUB-GROUP Detached breakwaters Pocket beaches ae a Race Empirical Design Method Reef breakwaters Headlands Segmented breakwaters 19, ABSTRACT (Continue on reverse if necessary and identify by block number) This report presents empirical relationships available in the literature for design and prediction of beach response to single, segmented, headland, pocket beach, and reef breakwater systems for the primary purpose of shore protection. The data set used to develop each design method is discussed, and the empirical procedures are evaluated based on available Corps=built breakwater project data, An existing US detached break- water project is used to intercompare design relationships and further assess their validity. Several empirical methods are shown to predict prototype response fairly well. These relationships may be useful in conjunction with detailed studies to quickly assess prototype response to various design alternatives. 20. DISTRIBUTION / AVAILABILITY OF ABSTRACT 21. ABSTRACT SECURITY CLASSIFICATION i CX) UNCLASSIFIED/UNLIMITED [J sAME AS RPT. — C1 otic USERS unclassified te : 22a. NAME OF RESPONSIBLE INDIVIDUAL 22b. TELEPHONE (Include Area Code) | 22c. OFFICE SYMBOL DD Form 1473, JUN 86 Previous editions are obsolete. SECURITY CLASSIFICATION OF THIS PAGE OT el SECURITY CLASSIFICATION OF THIS PAGE EEE SECURITY CLASSIFICATION OF THIS PAGE PREFACE The study summarized in this report was authorized by the Headquarters, US Army Corps of Engineers (HQUSACE), and performed as a part of the Civil Works Research and Development Work Unit 32535, "Engineering Performance of Coastal Structures." Mr. John H. Lockhart, Jr., was HQUSACE Technical Monitor. Funds were provided through the Coastal Engineering Research Center (CERC), US Army Engineer Waterways Experiment Station (WES), Vicksburg, MS. Work was performed under the general supervision of Dr. Yen-hsi Chu, Chief, Engineering Application Unit (EAU), Coastal Structures and Evaluation Branch (CSEB), Engineering Development Division (EDD), CERC; Ms. Joan Pope, Chief, CSEB; Mr. Thomas W. Richardson, Chief, EDD; Dr. C. Linwood Vincent, Program Manager, CERC; Mr. Charles C. Calhoun, Jr., Assistant Chief, CERC; and Dr. James R. Houston, Chief, CERC. This report was prepared by the Principal Investigator of the work unit, Ms. Julie Dean Rosati, Hydraulic Engineer, EAU, CSEB. COL Larry B. Fulton, EN, was Commander and Director of WES during the publication of this report. Dr. Robert W. Whalin was Technical Director. CONTENTS PREFACE LIST OF FIGURES. PART I: INTRODUCTION PART II: TECHNIQUES FOR DETACHED BREAKWATER DESIGN . Overview Se eoshan no fe Empirical Relationships PART III: ASSESSMENT OF DESIGN TECHNIQUES Introduction . Evaluations. PART IV: SUMMARY AND RECOMMENDATIONS REFERENCES APPENDIX A: NOTATION . 16 it LIST OF FIGURES Definition of terms used in this report Equilibrium salient formation . Equilibrium tombolo formation . ‘ Morphological response as a eancelont of ssancereell maseemintora Relationship to predict gap erosion for pocket beaches Effect of gap spacing on sand deposition to lee of breakwater Effect of gap pesca eoe on sand deposition for each breakwater gap pair 3 : acne Effect of gap epee ine on Penna depesciont for ap copilon 3 Relationship to predict gap erosion for headland structures Evaluation of morphological relationships : Evaluation of Suh and Dalrymple’s (1986) relationship fon sellin length Combined eeatencion oe Herete Pata Heroren? s (1986) were Nir’ s (1982) relationships SACI ar (at ie teae a eect ee Gee Oa ct a na roe EAC aot: Be Evaluation of Seiji, Uda, and Tanaka's (1987) limits for gap ero- sion See Urs, Bete A Penne pre bane ont eet Evaluation of Berenguer and Enviquec’ (1988) and Ahrens’ relation- ships for pocket beach gap erosion Evaluation of Hallermeier'’s (1983) ‘elationship con peenccere dosage depth . : : Lakeview Park Droleet Per aneeers as dlastigaed “ehaa IMC mecnodl Lakeview Park project as constructed (Diffraction Energy Method) FUNCTIONAL DESIGN OF BREAKWATERS FOR SHORE PROTECTION: EMPIRICAL METHODS PART I: INTRODUCTION 1. The increase in public use of coastal areas during the 20th century and a gradual relative sea level rise in many areas of the world have made beach stabilization a priority for those who use coastal regions. An ideal form of shore protection is one that would allow long-term stabilization of an area in a cost-effective manner, protect upland structures to some degree during storms, and provide an aesthetic recreational area, while avoiding undesirable adjacent beach effects. All forms of shore protection (i.e., groins, breakwaters, seawalls, revetments, bulkheads, beach-fill, etc.) have certain disadvantages; however, the shore-parallel breakwater, placed at the shoreline or offshore and designed either to intercept a portion of longshore- moving sediment or to protect a placed beach-fill, has the potential to perform close to the ideal for many types of coastal environments. 2. Breakwaters provide protection to a length of shoreline by dissipat- ing, reflecting, and diffracting incoming wave energy. Pope (1989) and Dally and Pope (1986) discuss the terms that have evolved to describe the different functional behaviors of the shore-parallel structure. Headland breakwaters are constructed at or very near the original shoreline, designed to promote beach growth out to the structure (tombolo formation) during all or part of the water-level cycle. These structures tend to function as a transmissible groin, intercepting all or a portion of the longshore-moving material. Pocket beach breakwaters are a class of headland breakwaters, used to provide protection to a placed beach-fill that is usually retained in the longshore direction by terminal groins. The protected shoreline may extend partially out towards the structure (termed a salient), or a tombolo may form. Detached breakwaters are constructed at a significant distance offshore of the original shoreline and interact with incoming wave energy to produce a quiescent region landward of the structure. Depending on structural and site parameters (structure length, distance offshore, transmissibility, wave climate, etc.), morphological beach response may be either a salient or tombolo. Reef breakwaters are a type of detached breakwaters constructed with a low crest 4 elevation, therefore allowing a significant amount of wave energy into the protected area. The beach response to these types of structures is usually a salient; these structures may be advantageous for sites where the interruption of the horizon by a structure is considered unaesthetic. Unless otherwise noted, reef breakwaters have been grouped with detached breakwaters, and pocket beach breakwaters with headland breakwaters, throughout this report. For projects with relatively short alongshore distances to protect, a single breakwater is often sufficient. For longer length projects, a series of structures may be required to protect the project beach; this series is termed a segmented system. 3. Unlike shore-perpendicular structures (i.e., groins), which impound sediment and ultimately starve downdrift beaches, detached breakwaters can be designed to allow material to pass through the sheltered region, minimizing their impact on adjacent shorelines. Onshore, shore-parallel structures such as seawalls, revetments, and bulkheads are designed to prevent retreat of the landward region they protect and do nothing to reduce erosion of the beach. Beach-fill reduces the storm impacts to upland structures, while providing a recreational beach; however, the quantities of replenishment required for maintenance may be cost-prohibitive. The use of detached or headland break- waters in combination with beach-fill may provide a cost-effective alternative to beach-fill alone for many coastal regions. 4. Although the breakwater appears to have advantages over the other traditional forms of shore protection mentioned above, use of this form of shore protection has been minimal in the United States. Seventeen detached breakwater projects (46 breakwater segments) exist along 9,200 km of the continental US and Hawaiian shorelines. Seventy-one additional segments either are in the early stages of construction or are planned for construction within the next few years by the US Army Corps of Engineers” (Gorecki and Pope in preparation). Comparatively, at least 4,000 detached breakwater segments exist along Japan's 9,400-km coast (Seiji, Uda, Tanaka 1987; Japanese Ministry of Construction (JMC) 1986); 15 segments provide protection to the 300 km of Israeli Mediterranean shoreline (Goldsmith and Sofer 1983); and Personal Communication, 1989, Edward Fulford, Chief, Coastal Planning Section, formerly US Army Engineer District (USAED), Baltimore, Baltimore, MD, and Thomas Bender, Chief, Coastal Engineering Section, USAED, Buffalo, Buffalo, NY. 5 80 breakwater segments have recently been constructed on the Danish North Sea coast (Laustrup 1988). Shore-parallel structures for shore protection have also been used in Spain (Berenguer and Enriquez 1988) and Singapore (Silvester and Ho 1972; Chew, Wong, and Chin 1974) and are being evaluated for a major coast protection scheme in Negombo, Sri Lanka (Danish Hydraulic Institute 1988). The documented performance of these structures in Japan and Israel demonstrates that this type of shore protection is both effective and versa- tile, successfully performing in low to moderate wave energy environments with sediment ranging from fine sand to pebbles. 5. A primary reason breakwaters have been under-utilized in the United States is the lack of functional design guidance. Techniques to predict beach response in the project area and on adjacent shores as a function of struc- tural and site parameters may be unreliable, unproven, cost- and time- intensive, or not readily available to the project designer. Other factors limiting the use of breakwaters in the United States include the high cost of water-based construction (used in most cases for detached breakwaters) and an inability to predict and compensate for structure-related phenomena such as adjacent beach erosion, rip currents, scour at the structure base, and the effects of structural settlement on project performance. 6. The purpose of this report is to present and evaluate the various empirical breakwater design methods available to the project engineer. In Part II, the major categories of design techniques available are briefly presented, and empirical design relationships available in the literature are discussed with a common definition of terms. The methods described in Part II are evaluated in Part III using data available from several US projects. In Part IV, the empirical design techniques demonstrated to predict prototype response to detached breakwater systems are recommended for use by field engineers. Variables used throughout the report are defined in Appendix A. PART II: TECHNIQUES FOR DETACHED BREAKWATER DESIGN Overview 7. Techniques for designing detached breakwater systems can be classi- fied into three categories: models, which numerically or physically simulate coastal response to a proposed design; empirical methods, which relate proposed project variables to beach response based on observed prototype and model results; and prototype assessment, in which a version of the final design is constructed, evaluated, and refined in the field. Each design classification has inherent advantages and disadvantages. 8. Numerical and physical models are powerful tools that can give detailed information about coastal response to a particular design; however, a detailed prototype data set is usually required for calibration, verification, and simulation. The shoreline response model GENESIS (GENEralized SImulation model for Shoreline Change) is designed to simulate beach response to a variety of erosion control structures and was successfully used to simulate shoreline change at the Lakeview Park breakwater project (Hanson and Kraus 1989). Physical model tests can be expensive and time-consuming, and numeri- cal model simulations can mislead the designer through model instability or accurate solutions to inaccurate input conditions. Empirical relationships are quick, inexpensive methods for evaluating beach response to a proposed design; however, often the relationships have oversimplified design variables and expected prototype response. Empirical relationships rarely are able to predict complicated structure-induced phenomena such as the formation of rip currents in the vicinity of the project, or the extent of project influence on adjacent beaches. Where feasible, a prototype assessment of a proposed design is the best method for refinement of the final design. However, a prototype evaluation may be prohibitively expensive, and the construction of a poor design alternative may make it publicly and politically difficult for funding of the final project. 9. To ensure a successful project, the iterative use of various design techniques is recommended. Dally and Pope (1986) suggest a three-phase design process: first, a desk-top study employing various empirical relationships to identify design alternatives; second, either a physical or numerical model 7 study to assess and refine alternatives; and finally, if time and funding allow, a prototype test to verify and adjust the preliminary design. Initial use of empirical design methods can also provide a means of assessing model performance. Numerical and physical models, once calibrated and verified, can be used to extend and improve empirical relationships. Prototype assessment of a design alternative can provide data for refinement of empirical relation- ships and model calibration/verification. 10. The design methods that will be presented and evaluated herein are various empirical relationships for iterative use throughout the project design. These relationships include those that have been used to design US and foreign detached breakwater projects, and those recently developed through prototype and physical model evaluation. Empirical Relationships Introduction 11. Prior to utilizing techniques for any type of structure design, the functional intent of the project must be well-defined. Parameters such as the length of shoreline to be protected, design beach width, and acceptable adjacent beach erosion/accretion should be delimited. A breakwater project can be designed in segments, to protect a long length of shoreline, for salient or tombolo formation, or both. In the case of a site with a sig- nificant longshore transport rate adjacent to beaches that cannot tolerate much project-induced beach change, the design beach response should be a salient. A salient allows littoral movement of material to continue shoreward of the structures, minimizing project impacts on adjacent shores. If impacts to adjacent beaches are not of concern, the breakwater system could be designed for tombolo formation, maximizing project beach accretion. A common nomenclature for all relationships will be used throughout this report and is presented in Figure 1. All variables used throughout the report are defined in Appendix A. 12. The empirical relationships presented herein are generally orga- nized from the simpler to more complex design techniques and comprise a review of all studies that have recommended empirical relationships or methods for the design of breakwater systems. A general review of detached breakwater 8 BREAKER LINE INITIAL BEACH-FILL SHORELINE EQUILIBRIUM : a NO ORIGINAL SHORELINE SHORELINE —/ 500 | WEE “i Figure 1. Definition of terms used in this report references can be found in Lesnick (1979). 13. The most-investigated effect of detached breakwaters is the relationship between project accretion, in particular, morphological response (salient or tombolo), and structural parameters. Similar simple relationships between structure length and distance offshore have been proposed by various researchers. Inman _and Frautsch 1966 14. Based on observations of beach response at the 434-m-long single detached breakwater at Venice in Santa Monica, CA, Inman and Frautschy (1966) observed that pronounced accretion did not occur for the following condition: L . a a < 0.17 - 0.33 pronounced accretion did (1) not occur where L, is the breakwater segment length, and X is the breakwater segment distance from the original shoreline. Nir (1982) 15. Based on project performance of 12 breakwaters on the Israeli coast, Nir (1982) concluded that accretion is very low or does not occur at all if the segment length to offshore distance ratio has a value of 0.5 or less: L Si Hoos ae < 0.5 nondepositional condition @) Assuming that the planform of the tombolo/salient formed a trapezoid, Nir calculated the area and volume of each spit out to the depth of structure. Dividing the volume by the area, Nir calculated the average sand thickness in the tombolo/salient z, and related it to the structure-distance ratio as follows (note that the equation is dimensionally inconsistent): z, (m) = 1.786 - 0.809 (+ (3) s The relationship was developed from prototype data with X/L, values ranging from 0.38 to 2.0, resulting in sand thicknesses ranging from approximately 0.3 to 1.7 m. Seven out of the twelve structures developed tombolos. Beach response for the Israeli breakwaters was observed to reach a mature age about 5 years after construction was completed; adjacent beaches suffered severe erosion during the first 3 to 4 years (or longer) after construction. Gourlay (1981) 16. Gourlay (1981) presents similar relationships based on physical model and field observations. Based on the laboratory studies of Sauvage de St. Mark and Vincent (1955), Adachi, Sawaragi, and Ogo (1959), and Shinohara and Tsubaki (1967), Gourlay reaches the following conclusions for laboratory response to detached breakwaters: a. Tombolos can form only if the structure is located in the surf zone. b. Noninterfering diffraction patterns, resulting in two independent current systems (and possibly double tombolo formation), exist for the following structure-distance ratio: 10 al) ih, a) ae (4) ce. Diffraction patterns interfered and reduced longshore currents for a lower range of the ratio. Beach response was observed to be either a salient if bed load was the dominant transport mechanism (fall velocity parameter, H,/VIT < 1.5 , where H, is the deepwater wave height, V is the sediment fall velocity, and T is the wave period), or a more complex feature if suspended load transport dominated (H,/VT > 1.5): +s ¢0.4 to 0.5 (5) x d. Noninterfering currents strong enough to transport material resulted in tombolo formation for an intermediate ratio value: Ls — =0.67 to 1.0 (6) xX 17. Gourlay makes the following observations about beach response to prototype breakwaters based on performance of structures in California, Japan, and Israel: a. Tombolo formation can only occur if the structure is inside the surf zone and Ls iatsi ; 7 =e > acd (7) Io For cases in which the structure is outside the surf zone, the seaward extent of the beach response (salient) is determined by the breaking point location. Rosen and Vadja (1982 18. Rosen and Vadja (1982) graphically present relationships to predict the equilibrium salient and tombolo size based on structure and site parame- ters. Relationships to predict salient formation are based on a physical model study of beach response (0.64-mm sand) to an impermeable breakwater under normal wave incidence conducted by Rosen and Vadja, including laboratory data measured by Shinohara and Tsubaki (1967) and prototype data from Israeli, 11 US, and Japanese structures. Given a desired salient length in the on- offshore direction (measured from original shoreline) X and a dimension- s? less breaker distance X,/X , where X, is the distance from the original shoreline to the mean breaker line, the recommended ratio L,/X can be graphically determined (Figure 2). 19. Several relationships are also presented for determining tombolo size in the equilibrium state, based on the field data of Inman and Frautschy (1966), Toyoshima (1976), and Nir (1976) (Figure 3). Given project variables L, , X , and beach slope I , the following parameters can be estimated: the volume of sand trapped in the tombolo Q , length of tombolo in alongshore direction (measured at structure) Ly; , and area of tombolo Ay, Shore Protection Manual (SPM) (1984) 20. Based on the pattern of diffracting wave crests in the lee of a breakwater, the US Army Corps of Engineers’ Shore Protection Manual (SPM 1984) recommends that the structure length be less than the distance offshore to inhibit tombolo formation: L = < 1.0 tombolo formation prevented (8) This structure-distance ratio usually allows diffracting wave crests to intersect in the shadow zone of the structure prior to undistorted wave crests reaching the adjacent beach. For normal wave approach, the approximate location of the salient apex is the intersection of the diffracting wave crests as they reach the shoreline. 21. The SPM recommends the following limit to ensure tombolo formation: L ras 2.0 tombolo formation certain (9) Dally and Pope (1986 22. Dally and Pope (1986) recommend limits of the structure-distance ratio based on the type of shoreline advance desired (either nonuniform, where salients or tombolos occur, or uniform, in which an equal advance of the beach occurs), and the length of the beach to be protected. For nonuniform 12 Lox 0.3 0.2 0.1 DIMENSIONLESS VARIABLES LEGEND ROSEN AND VADJA (1982) 0.68 SHINOHARA ET AL (1966) 0.85 NATURE ISREAL 0.45 NATURE U.S.A. o NATURE JAPAN 1.50 — — LINES OF CONSTANT xe >1.3 certain erosion opposite gap (32) Noble (1978) 31. Noble (1978) evaluated the effects of detached structures along the California coast and those discussed in the literature and concluded that "detached breakwaters produce only minimal impact when the offshore distance of the structure is greater than six times the breakwater length." That is, L “s ¢ 1 minimal impact (33) x 6 Noda (1984) 32. Noda (1984) conducted a series of movable-bed (0.2-mm sand) laboratory experiments evaluating physical parameters controlling the develop- ment of tombolos and salients, especially due to on-offshore transport. Noda used both storm and swell-type waves and concluded that maximum deposition occurs when ODS se ee (34) Zl 33. Well-developed tombolos were observed to form when Pr Cape and a bimodal tombolo developed for Xe The total amount of sand deposition per unit width of gap was observed to be about three times the quantity of material transported shoreward through a permeable breakwater, when dimensions of the structures are "chosen appro- priately." When structures were placed seaward of the breaker line, no sand was observed to move seaward through the structures; when structures were placed near the shoreline, Noda observed that sand may move offshore. Hallermeier (1983) 34. In a review of field and laboratory sediment depositional patterns in the vicinity of coastal structures, Hallermeier (1983) developed a rela- tionship for the depth limit of sediment transport. Hallermeier recommends the following depth as a guide when positioning detached breakwaters when tombolo formation is deemed undesirable: ZRH 110 He dgg = oe -~ ———*— _ depth for salient formation (37) VS =D) (Eis al) ef 45 where d,, = annual seaward limit of the littoral zone H, = deepwater wave height exceeded 12 hr per year S = ratio of sediment to fluid density g = acceleration of gravity T, = wave period corresponding to H, 35. For headland structures (tombolo development), structures should be sited near d= a headland structures (38) 22 Suh_and Dalr le (11987 36. Based on unscaled monochromatic movable-bed laboratory tests, Suh and Dalrymple (1987) give relationships for salient length, xX, , given s structure length L, and location in surf zone for single offshore breakwa- ters: Xp X, = 0.156 L, = <0.5 Rion (39) Xp Xe = 0.317 L, Oe SS Eo) R= 1OMS'5 (40) X» Xe OST as = 21.0 R = 0.75 (41) where R_ is the correlation coefficient. 37. Combining the laboratory results with available prototype data, the following relationship for salient length is obtained: -2.83 ,{ —2— ] 5 3 Oe (GIL 8) i i . #0 (42) Ss Tombolos usually formed for single prototype breakwaters when =o 341.0 (43) For multiple offshore breakwaters, tombolos formed when eeeX rie Os (44) Ls Harris and Herbich (1986) 38. Harris and Herbich (1986) conducted a series of movable bed (Ds) = 0.63 mm) monochromatic physical model tests to evaluate the effect of 23 detached breakwater gap spacing on sand entrapment. Relationships for the average quantity of sand deposited to the lee of each breakwater, Q, , both to the lee of the breakwater and in the gap area, (Q, + Q,) , and in the gap area alone are presented in Figures 6 through 8. Combining model results with prototype data, Harris and Herbich relate the dimensionless accreted volume to structure parameters as follows: fe) 0.32 - 1.92( Wicd = al (z ) (45) The relationship is based on data with values of X/L, ranging from 0.5 to Bes 2 Sonu_and Warwar (1987 39. Sonu and Warwar (1987) empirically relate the growth of the Santa Monica, CA, tombolo through time as follows: (ots (0), Malo?) (46) 0.4 Q,/XLsd Figure 6. Effect of gap spacing on sand deposition to lee of breakwater (after Harris and Herbich 1986) 24 Qg/XdL g 0.3 LEGEND > 0.2 + res = ay OY ~ D + a (o] (¢) A ec ey 0.6 0.7 0.8 0.9 1:05 teat 1e2: 1.3 Figure 7. Effect of gap spacing on sand deposition for each breakwater gap pair (after Harris and Herbich 1986) OG A UGY 1O® OL [OSs A Male en SESE tas OG X/Ls Figure 8. Effect of gap spacing on sand deposition for gap region (after Harris and Herbich 1986) 25 where Q, is the volume at final equilibrium state, equal to 2,100,000 cu tere yd" for the Santa Monica breakwater and A is an empirical coefficient, 1 determined as 0.104 year. The authors conclude that, without dredging events, the Santa Monica breakwater would have reached 90-percent growth in 22 years. Silvester and Ho (1972) 40. For beaches that have equilibrated with headland structures, Silvester and Ho (1972) present a relationship to predict the maximum gap indention (X + X,) given a gap distance L, and predominant wave direction B (degrees) (Figure 9). Japanese Ministry of Construction (1986 41. The empirical method of breakwater design described by the JMC in their "Handbook of Offshore Breakwater Design" (1986) has several advantages over the empirical relationships presented previously. The JMC method is a step-by-step iterative procedure, allowing the designer to follow specific LEGEND VICHETPAN EXP. HO EXP. PROTOTYPE BAYS TYPICAL BAY BEDOCK SINGAPORE (X + Xg)/ Lg PREDOMINANT WAVE DIRECTION B° Figure 9. Relationship to predict gap erosion for headland structures (after Silvester and Ho 1972) rete To convert cubic yards into cubic metres, multiply by 0.7645549. 26 guidelines towards the final design. Rosati and Truitt (1990) discuss the JMC method of breakwater design and present several example problems. 42. However, the JMC method has its disadvantages for use in design of US detached breakwater systems. Approximately 60 percent of the projects on which the method is based resulted in tombolo formation; therefore, it is more appropriate for headland or pocket beach-type systems, rather than detached breakwater or reef systems. Unlike US breakwater projects, beach fill is not placed as a part of the JMC's projects; therefore, there is no provision for beach fill in the iterative method. All structures considered in the JMC study were permeable; however, the effect of increased or decreased structure transmissibility is not included in the JMC method. For construction of a highly transmissible structure such as a reef breakwater or perched beach, use of the JMC method for design is most likely inappropriate. The wave height required for input is the average of the highest five nonstorm waves that occur in a typical year and corresponding wave period, often difficult parameters to extract from typically available hindcast wave data sets. The effects of a variable water level on design are not explicitly accounted for in the procedure. 27 PART III: ASSESSMENT OF DESIGN TECHNIQUES Introduction 43. To evaluate the empirical design methods presented in Part II, data from five US breakwater projects have been compiled (Table 1) and prototype response compared with that predicted by the relationships. Variables presented in Table 1 are defined in Appendix A. These projects encompass a range of structural and site parameters and observed beach response, from salient formation (Lakeview Park and Redington Shores), to no beach response (Lakeshore Park), and periodic tombolo formation (Colonial Beach, Central and Castlewood Park Beaches). Evaluations Morphological response 44. Two types of predictive relationships were discussed that relate to morphological response: those that predict a nondepositional, salient, or tombolo response as a function of structural parameters; and a relationship predicting seaward salient excursion. By far, the majority of the relation- ships presented fall into the first category; an evaluation of these relation- ships by author is presented in Figure 10. Dashed horizontal lines in the figure separate the boundaries between the indicated morphological responses; solid lines indicate the range recommended by the cited author. 45. A trend is apparent in the prototype data for deposition to increase as the structure length to distance offshore ratio increases. However, the ability of the relationships to accurately predict observed response is at best fair. If other types of design tools are available, it is recommended that these simple empirical relationships be used only as a general guide when designing a project. 46. Suh and Dalrymple’s (1987) relationship for salient length (Equa- tion 42) was applied to all segmented projects (Equation 42 does not apply to single structures since gap distance L, is not defined). The relationship g tends to overpredict the seaward excursion of the spit for the majority of prototype data evaluated (Figure 11), but appears to predict very well for the 28 Table 1 Corps-Built Breakwater Data Segment/ R Abbrev- cae Q4 Ls Lg Xj xX din xsy X, Lo Hy T Xei Xp Dso Beach Project iation m m m m m m ut nm m m m m sec m m mm Response Lake- 390 84,106 view Park West 76 49 55 US sW} SoS) —Oes} 16 98 2.0 4.6 -18 Soed (5) nondepo- (LV1) sitional Center 76 49 55 U3, BORN Sash ae) Ay ales Be AG: 3 Oe ‘0.5 salient (LV2) East 76 49 46 UPA SOR) SIGS) EIS} SAl LOSI 20h 4i(6ri 1 Ole Shee O)55) salient (LV3) Lake- 244 28,290 shore Park West 38 61 49 Tine OT 2h an Gy elt) Ue) “Sel Work AG} -18 0.23 salient (LS1) Center 38 61 54 960 201-19) 55), 19 CE velo 7/6c40 C8} -11 0.23 salient (LS2) East 38 61 45 BSP 201 1-9) 52 -8 UPA. S33.) 573 SS} -11 0.23 salient (LS3) Reding- 312 23,000 ton Shores Single 112 22 85 95 .05 2.4 22 CPS AA GO) = ac4 Sila -6 0.14 salient (RS) Colonial 460 40,370 Beach, Central Upriver 61 46 15 Go MOS eo to 6 58) OT eiN4 4.16 = 12) 38 0.5 tombolo (CB1) Center- 61 46 15 65h 0 2mda2 15 65) LOST as 14716. 5-8; 42 0.5 tombolo upriver (CB2) Center- 61 46 15 65) 7.02) 01.9 14 64 Oy alg ia: ot) 42 0.5 tombolo down- river (CB3) Down- 61 46 15 65571027019) 14 64 101 1.4 4.6 -15 35 0.5 tombolo river (CB4) Colonial 325 11,470 Beach, Castle- Upriver 91 46 14 24 .01 0.6 14 24 aa Ay 65 52 Alt 0.5 tombolo wood (CP1) Park Center 61 37 13 242401 0N6rao8 15 TO gO OsG ass Sheth 0.5 salient (CP2)) Down- 61 27 15 24 .01 0.5 4.2 13 Oe 4 465-10) 0/18 0.5 salient river (CP3) Ly = Alongshore project length; Q; = Quantity of beach-fill placed in project area; X,; = Breakwater segment distance from initial beach-fill shoreline; X,; = salient/tombolo length in on-offshore direction measured from initial beach-fill shoreline; X,, = Erosion/accretion opposite gap, measured gi from initial beach-fill shoreline. 29 sdtysuotjepTer [eotsoToydazow Fo uotqenyteaqg “OL ain3ty XTX fae Ls 9 c v ¢ A L 0 C) eee 5 SINIOd VIVG JO Y3IEWNN SILVOIGNI ae ane z YOHLNV G3LID AG GIGNANNODIY JONVY pa Oo x/*1 t ” (zmlavi 33S) Viva 3dALOLONd $ a re ntanen - aNa931 (ssaud NI) XOD ® SNIYHV Ah S (zee!) YIN > JVNOILISOd3GNON (9961) AHOSLNVUs ®% NVWNI —>| UE LN3NVS @ C) ee @@ (z)e + t+tt+ (z) (Z) “Nn > = m Zz = (2961) (avi) IdNANIVG ¥ HNS } (ssaud Np XOO ® SN3YHV (9861) 3dOd ® ATIVG —s| je — (¥861) Wds -_ ee AIN3NnVS (1861) (avi) avlunod O1OEWOL (SS3ud NI) XO9 SNIYHV (v264 ‘7264 En Sa ee (9861) (STSNIS) 3d0d > ATIVG —e| ~—— (9861) (G3LN3N93S) 3dOd *% ATIVG a Mae She Se eS ee ee ae RE ee) nds = { O1OENOL 80 60 cB, 0 a 2.3.4 PERFECT AGREEMENT E 40 v LEGEND xa) CB: Central Beach v CP: Castlewood Park av LS: Lakeshore Park : LV: Lakeview Park 20 (0) -20 21 eee | —20 fe) 20 40 60 X,. Measured, m Figure 11. Evaluation of Suh and Dalrymple's (1986) relationship for salient length pocket-beach type structures with periodic tombolo formation (Central\Beach and Castlewood Park Beach). The correlation coefficient R is equal to 0.67. 47. Because data defining the equilibrium volume and spit thickness to the lee of each breakwater segment were not readily available for US projects, a direct comparison between Harris and Herbich's (1986) volumetric and Nir’s (1982) thickness relationships (Equations 45 and 3, respectively) could not be performed. However, the measured spit area was directly compared with a pre- dicted area value using Harris and Herbich’s volumetric relationship divided by Nir's spit thickness parameter. It should be recognized that this combined evaluation is not a true assessment of either method; however, it does give an indication of whether the combined relationships are accurate in predicting spit area. The measured spit area is calculated by assuming a triangular shape of the salient/tombolo. Much scatter is apparent in the comparison (Figure 12), with a correlation coefficient equal to 0.18. 48. Seiji, Uda, and Tanaka’s (1987) ranges to predict gap erosion (Equ- ations 30 through 32) were evaluated (Figure 13). The lower boundary for Sk ORs LEGEND 6000 CB: Central Beach CP: Castlewood Park LS: Lakeshore Park LV: Lakeview Park RS: Redington Shores LWA Ia) Ly, 4000 OLY, a ie xo) a Pe} $ PERFECT AGREEMENT ¢ a 2000 3 a ca < 0 -2000 -1000 0 1000 2000 3000 Area = 0.5(X%s Lo), m2 Figure 12. Combined evaluation of Harris and Herbich's (1986) and Nir's (1982) relationships 40 2) "NO EROSION” siete Shue EROSION” a a 20 La “onl Be ese CERTAINIRE ROS ONS a yt te yn ee = @ @ E ee “a 8 3 @) oS d a Sn 2 -20 Sas z @ = LEGEND 40. om e tg/Xx w fF ) a La/X} a 2) NUMBER -~60 % (2) OF DATA POINTS 0 1 2. 3 4 5 6 7 Lg/X , Lg/X, Figure 13. Evaluation of Seiji, Uda, and Tanaka's (1987) limits for gap erosion 32 "no erosion" (L,/X < 0.8) was a reasonably good predictor of either accretion or very little erosion. Gap erosion occurred for ratios of L,/X greater than 0.8. 49. Berenguer and Enriquez’ (1988) and Ahrens’ formulae to predict gap erosion (Equations 26 and 29, respectively) for pocket beaches were evaluated using data from the two sites at Colonial Beach (headland structures). Both relationships are inversely proportional to the data (Berenguer and Enriquez: R= -0.99, Ahrens: R= -0.24) (Figure 14). Structure depth 50. Hallermeier'’s (1983) relationship for recommended structure depth was evaluated using the recommended depth for salient formation (Equation 37) for all sites except Colonial Beach, where the recommended depth for tombolo formation (Equation 38) was used (Figure 15). An excellent correlation between depth at the structure and Hallermeier'’s recommended depth exists for all but the Lakeshore Park data, resulting in a correlation coefficient Ra AOSD 50 LEGEND 40 + Berenguer and Enriquez (1988) Ye O Ahrens (personal communication 1989) CB: Central Beach 30 CP: Castlewood Park E 3 20 a 2 ne) 2 = 00 G, PERFECT AGREEMENT x< 0) -10 —20 —20 0) 20 40 Xq. Measured, m Figure 14. Evaluation of Berenguer and Enriquez’ (1988) and Ahrens’ relationships for pocket beach gap erosion 33 JMC method 51. As mentioned in Part II, the JMC method of breakwater design has limitations for use with typical US projects: beach fill is not included as a part of the design method; guidance is based on data from sites at which tombolo formation occurred for the majority of cases; wave conditions required for design are the wave height and period corresponding to the "average of the largest five nonstorm waves occurring in a typical year"; and the effects of structural transmissibility and water-level variations are not parameters in the method. A comparison of the JMC and typical US design using data from the Lakeview Park, Lorain, OH, detached breakwater project was presented by Rosati and Truitt (1990). Figure 16 presents project parameters resulting from the JMC method, which can be compared with the as-constructed parameters resulting LEGEND Central Beach Castlewood Park Lakeshore Park Lakeview Park Redington Shores PERFECT AGREEMENT Hallermeir’s Recommended Depth, m oe, 0.4 0.8 AZ. 1.6 2 2.4 2.8 3.2 3.6 Depth at Structure, m Figure 15. Evaluation of Hallermeier’s (1986) relationship for structure design depth 34 <-> Lo= 2:L= 80m X,g= 26m Lp = 390m Figure 16. Lakeview Park project parameters as designed with JMC method (Rosati and Truitt 1990) from the Diffraction Energy Method (Walker, Clark, Pope 1980; see discussion in Part II) (Figure 17). The four example problems conducted by Rosati and Truitt (1990) indicated that, for the site parameters evaluated, use of the JMC design tended to result in "more numerous, shorter length segments with a decreased gap width . . . structures are placed closer to shore than observed in US projects." Lge 62m d= 3.8m Lg= 49m 5a aa ee 26m Lp= 390m $?V—XMRl Figure 17. Lakeview Park project as constructed (Diffraction Energy Method) (Rosati and Truitt 1990) 35 Comparison of methods 52. Using the design relationships presented in Part II, the Lakeview Park project has been used to intercompare relationships and further assess their validity. This project was chosen for use because it is representative of US projects, has been successful in protecting the project beach, and has already been designed using the JMC and Diffraction Energy Methods. Recom- mended project parameters using Toyoshima’s (1972, 1974) median-depth system were also calculated for comparison. Linear wave theory was used to bring deepwater waves to the structure, and the structure depth using Toyoshima's method was the same as the as-constructed depth. The various design parame- ters resulting from each method are presented in Table 2. Table 2 Lakeview Park Structural Parameters Corresponding to Design Method Method Ii loa) hi X, m d, m Ee X Diffraction 76 49 15, Be 1.04 Energy (as constructed) JMC 40 23 39 1.6 103: Toyoshima’s Median- 60 24 18-40 352) e303 Depth System 53. The JMC method resulted in a smaller structure length, gap dis- tance, and distance offshore from the original shoreline as compared with the as-constructed parameters. Toyoshima's median-depth system resulted in a larger segment length and gap distance than the JMC method, but distance off- shore was equal to or less than the other two methods. The range in recom- mended structure distance offshore is quite large using Toyoshima’s method. Using values of the structure length-to-distance offshore ratios for each method with the predictive relationships discussed in Part II (also illustrat- ed in Figure 10), the most likely morphological response corresponding to each method can be predicted. The majority of the relationships indicate that the most likely beach response for all three methods would be tombolos. However, the morphological response in the prototype is salients. 36 54. Suh and Dalrymple's relationship predicts salient lengths xX, (Equation 42) equal to 72 and 39 m using project parameters obtained from the Diffraction Energy and JMC methods, respectively. These values differ from the design salient length (X, =26 m) used for both the Diffraction Energy and JMC methods. However, using an average distance offshore for Toyoshima’s method X = 29 m results in a predicted salient length equal to 24 m, very close to the prototype response. 55. Harris and Herbich’s (1986) relationship for salient volume (Equa- tion 45) predicted the largest volume of salient accretion if structural pa- rameters obtained from the Diffraction Energy method (4,200 m°?) were used, followed by Toyoshima's median-depth system (3,300 m®) (using an average dis- tance offshore equal to 29 m), then by the JMC method (540 m?). Since the values of L,/X are less than or approximately equal to 0.8, Seiji, Uda, and Tanaka's (1987) ranges to predict gap erosion (Equations 30 through 32) indi- cate that only a slight possibility for gap erosion exists for all sets of structural parameters. SH PART IV: SUMMARY AND RECOMMENDATIONS 56. An intercomparison of empirical design methods and predictive relationships such as presented in Part III may be useful in lending validity to certain design tools. However, it is difficult to make broad generaliza- tions about the reliability of empirical methods. The inherent simplicity of the empirical methods evaluated herein and the lack of a large prototype database tended to result in widely varying predictions for most design relationships. As with any research study, more prototype, numerical, and physical model data sets would greatly increase knowledge and predictive abilities. 57. However, several design methods and relationships were shown to be useful predictors, if their limitations are realized throughout the design process. Suh and Dalrymple’s (1987) relationship predicting salient length in the on-offshore direction tended to overpredict the salient excursion (R = 0.67), but was a very good predictor for pocket-beach type projects with tombolo formation. Dividing Harris and Herbich’s (1986) volume relationship by Nir’s (1982) salient/tombolo thickness relationship gave a prediction of the salient/tombolo area. The correlation between measured (assumed to have a triangular shape) and predicted area was weak (R = 0.18), but a trend was observed. Seiji, Uda, and Tanaka's limit for "no gap erosion" was shown to be a fairly good predictor. Berenguer and Enriquez’ (1988) and Ahren’s rela- tionships to predict gap erosion for pocket beaches, developed from pocket beach data in Spain, were poor indicators of actual gap erosion for US headland projects (R = -0.99, R= -0.24, respectively). Hallermeier'’s (1983) recommended depth for breakwater projects was shown to correlate well to actual project depth for all but one project (overall R= 0.55). 58. The success of the Lakeview Park project lends validity to the method used to design it, the Diffraction Energy Method. A comparison of Lakeview Park as-constructed project parameters to those recommended by the JMC method and Toyoshima’s median-depth system was conducted. Both the latter two methods resulted in smaller segment lengths and gap distances than the as- constructed project. The structures were also positioned closer to shore than indicated by the Diffraction Energy Method. 59. As with any design procedure, limitations of any empirical method 38 must be realized throughout the design process. Empirical methods shown to be reasonable predictors herein can be useful as simple, inexpensive indicators of likely prototype response. Ideally, after a desk-top empirical design, the proposed project should be further evaluated with numerical and physical models, followed by a prototype test if time and funding allow. 39 REFERENCES Adachi, S., Sawaragi, T., and Ogo, A. 1959. "The Effects of Coastal Struc- tures on the Littoral Sand Drifts," Coastal Engineering in Japan, Vol 2, Japanese Society of Civil Engineers, pp 85-98. Ahrens, J. P., and Cox, J. "Design and Performance of Reef Breakwaters," submitted to Journal of Coastal Research, in press. Berenguer, J., and Enriquez, J. 1988. "Design of Pocket Beaches: The Spanish Case," Proceedings, 21st International Coastal Engineering Conference, pp 1411-1425. Chew, S. Y., Wong, P. P., and Chin, K. K. 1974. "Beach Development Between Headland Breakwaters," Proceedings, 14th International Conference on Coastal Engineering, June 24-28, Copenhagen, Denmark, American Society of Civil Engineers, pp 1399-1418. Danish Hydraulic Institute. 1988. "Offshore Breakwaters, Negombo: Report on Physical Model Tests," Report prepared for Coast Conservation Department of Sri Lanka, Chapters 1-4. Dally, W. R., and Pope, J. 1986. "Detached Breakwaters for Shore Protec- tion," Technical Report CERC-86-1, US Army Engineer Waterways Experiment Station, Vicksburg, MS. Goldsmith, V., and Sofer, S. 1983. "Wave Climatology of the Southeastern Mediterranean: An Integrated Approach," Israel Journal of Earth Science, Vols 250 ppi lol Gorecki, R. J., and Pope, J. "Coastal Geologic and Engineering History of Presque Isle, Peninsula, Pennsylvania," Miscellaneous Paper in preparation, US Army Engineer Waterways Experiment Station, Vicksburg, MS. Gourlay, M. R. 1981. "Beach Processes in the Vicinity of Offshore Break- waters," Proceedings, Fifth Australian Conference on Coastal and Ocean Engineering, Perth, Australia, pp 129-134. Hallermeier, R. J. 1983. "Sand Transport Limits in Coastal Structure Designs," Proceedings, Coastal Structures '83, March 9-11, Arlington, Virgin- ia, American Society of Civil Engineers, pp /03-716. Hanson, H., and Kraus, N. C. 1989. "GENESIS: Generalized Model for Simulat- ing Shoreline Change; Report 1, Technical Reference," Technical Report CERC-89-19, US Army Engineer Waterways Experiment Station, Vicksburg, MS. Harris, M. M., and Herbich, J. B. 1986. "Effects of Breakwater Spacing on Sand Entrapment," Journal of Hydraulic Research, Vol 24, No. 5, pp 347-357. 40 Inman, L. D., and Frautschy, J. D. 1966. “Littoral Processes and the Development of Shorelines," Proceedings, Coastal Engineering, Santa Barbara CA, pp 511-536. Japanese Ministry of Construction. 1986. "Handbook of Offshore Breakwater Design," River Bureau of the Ministry of Construction, Japanese Government, translated from Japanese for the Coastal Engineering Research Center. Laustrup, C. 1988. "Erosion Control with Breakwaters and Beach Nourishment," Journal of Coastal Research, Vol 4, No. 4, pp 677-685. Lesnick, J. R. 1979. "An Annotated Bibliography on Detached Breakwaters and Artificial Headlands," CERC Miscellaneous Report No. 79-1, US Army Engineer Waterways Experiment Station, Vicksburg, MS. Nir, Y. 1976 (Mar). "Detached Breakwaters, Groynes and Artificial Structures on the Mediterranean Shore and Their Influence on the Structures of the Israeli Shore," Report No. 3, 76/2, Ministry of Industry and Commerce, Geological Institute, Marine Geology Section, Jerusalem (in Hebrew). Nir, Y. 1982. "Offshore Artificial Structures and Their Influence on the Israel and Sinai Mediterranean Beaches," Proceedings, 18th International Coastal Engineering Conference, American Society of Civil Engineers, pp 1837-1856. Noble, R. M. 1978. "Coastal Structures’ Effects on Shorelines," Proceedings, 17th International Coastal Engineering Conference, Sydney, Australia, American Society of Civil Engineers, pp 2069-2085. Noda, H. 1984. "Depositional Effects of Offshore Breakwater due to Onshore- Offshore Sediment Movement," Proceedings, 19th International Coastal Engineer- ing Conference, September 3-7, Houston, Texas, American Society of Civil Engineers, pp 2009-2025. Pope, J. 1989. "Role of Breakwaters in Beach Erosion Control," Proceedings, Florida Shore and Beach Preservation Association Conference, February 22-24, Tampa, Florida, in press. Pope, J., and Dean, J. L. 1986. "Development of Design Criteria for Segment- ed Breakwaters," Proceedings, 20th International Coastal Engineering Confer- ence, November 9-14, Taipei, Taiwan, American Society of Civil Engineers, pp 2144-2158. Rosen, D. S., and Vadja, M. 1982. "Sedimentological Influences of Detached Breakwaters," Proceedings, 18th International Coastal Engineering Conference, American Society of Civil Engineers, pp 1930-1949. Rosati, J. D., and Truitt, C. L. 1990. "An Alternative Design Approach for Detached Breakwater Projects," Miscellaneous Paper in preparation, US Army Engineer Waterways Experiment Station, Vicksburg, MS. 4l Sauvage de St. Mark, M. G., and Vincent, M. G. 1955. "Transport Littoral Formation de Fleches et de Tombolos," Proceedings, 5th International Con- ference on Coastal Engineering, Grenoble, American Society of Civil Engineers, pp 296-328. Seiji, M., Uda, T., and Tanaka, S. 1987. "Statistical Study on the Effect and Stability of Detached Breakwaters," Coastal Engineering in Japan, Vol 30, No. 1, pp 131-141. Shinohara, K., and Tsubaki, T. 1967. "Model Study on the Change of Shoreline of Sandy Beach by the Offshore Breakwater," Proceedings, 10th International Conference on Coastal Engineering, Tokyo, Japan, American Society of Civil Engineers, pp 550-563. Shore Protection Manual. 1984. 4th ed., 2 Vols, US Army Engineer Waterways Experiment Station, Coastal Engineering Research Center, US Government Printing Office, Washington, DC. Silvester, R., and Ho, S. 1972. "Use of Crenulate Shaped Bays to Stabilize Coasts," Proceedings, 13th International Conference on Coastal Engineering, July 10-14,Vancouver, B.C., Canada, American Society of Civil Engineers, Pp) 1347-13 65" Sonu, C. J., and Warwar, J. F. 1987. 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"Changes of Sea Bed due to Detached Breakwaters," Proceed- ings, 15th International Conference on Coastal Engineering, July 11-17, Honolulu, Hawaii, pp 1572-1589. 1982. "Variation of Foreshore due to Detached Breakwaters," Proceedings, 18th International Conference on Coastal Engineering, American Society of Civil Engineers, pp 1873-1892. US Army Engineer District, Buffalo. 1975. "Lakeview Park General Design Memorandum, Phase II, Project Design," Buffalo, NY. 42 Walker, J. R., Clark, D., and Pope, J. 1980. "A Detached Breakwater System for Shore Protection," Proceedings, 17th International Coastal Engineering Conference, Sydney, Australia, pp 1968-1987. 43 ae ak ran Saas ah ee oe mea 13 unk Ab Cesta wii i may ie ep) Ke] La | APPENDIX A: NOTATION Empirical coefficient Tombolo area Depth at structure Depth at gap between adjacent breakwater segments Depth at annual seaward limit of littoral zone Mean grain size of material in project area Acceleration of gravity (9.81 m/sec”) Deepwater wave height exceeded 12 hr/year Wave height at breakwater gap Design deepwater wave height Beach slope Beach response index Diffraction coefficient Wavelength at structure Alongshore distance between adjacent salients Alongshore distance between centers of adjacent breakwater segments Alongshore salient width, measured at original shoreline Gap distance between adjacent breakwater segments Deepwater wavelength corresponding to H, and T o Alongshore project length (length of shoreline to be protected) Breakwater segment length Tombolo length in alongshore direction, measured at structure Quantity of sediment in project area Quantity of sediment deposited to the lee of breakwater segment Quantity of sediment deposited to lee of breakwater gap Quantity of beach fill placed in project area Quantity of sediment at final equilibrium state Correlation coefficient Ratio of sediment to fluid density (2.65) Maximum stable beach-fill surface area Elapsed time Wave period corresponding to H, Al Wave period corresponding to H, Sediment fall speed Breakwater segment distance from original shoreline Distance from original shoreline to mean breaker line Erosion/accretion opposite gap, measured from original shoreline Erosion/accretion opposite gap, measured from initial beach-fill shoreline Breakwater segment distance from initial beach-fill shoreline Salient/tombolo length in on-offshore direction measured from original shoreline Salient/tombolo length in on-offshore direction measured from initial beach-fill shoreline Average sand thickness in tombolo/salient Predominant angle of wave approach A2 lige eset ors io i iis) aan | vi at hai its cs vor? a1 iy h ' DEPARTMENT OF THE ARMY WATERWAYS EXPERIMENT STATION, CORPS OF ENGINEERS BULK RATE 4909 HALLS FERRY ROAD VICKSBURG, MISSISSIPPI 39180-6199 US. POSTAGE PAID Vicksburg, MS Permit No. 85 Official Business CEWES-IM-MI-S 37907/012/91 DOCUMENTS LIBRARY/SMITH 206 WOODS HOLE OCEANOGRAPHIC INSTITUTION WOODS HOLE MA: 02543-1098