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HomeMy WebLinkAbout; ; Non-Structural Beach Erosion Protection; 1983-02-28NON-STRUCTURAL BEACH EROSION PROTECTION A PROJECT OF THE DEPARTMENT OF PUBLIC WORKS' AND TIDELANDS AGENCY CITY OF LONG BEACH, CALIFORNIA FEBRUARY 28, 1983 C1010 .8 LIBRARY of CaHsbad 2075 Las Palmasi&ve Carlsbad, CA 92009-4059 .^2 CITY OF LONG BEACH DEPARTMENT OF PUBLIC WORKS 333 WEST OCEAN BOULEVARD • LONG BEACH, CA 90802 • (213) 390-8922 I PREFACE "J J 1 1 1!-~ii i This report has been prepared to provide a consistent and compre- hensive summary of the events and the rationale which led to an attempt to resolve beach erosion problems for a high-value recre- ational and residential area in the City of Long Beach, California. It is hoped that the results of these efforts (whatever they may be) will prove to be helpful to others as the search for relatively low- cost measures for the protection of the coastline for recreational and residential uses continues. The search would not have been possible without the support and encouragement of city officials, members of the affected public and interested technicians too numer- ous to mention. Nevertheless, their encouragement is gratefully acknowledged. JAMES T. POTT DIRECTOR ENGINEERING DEPT. LIBRARY City of Carlsbad 2075 Las Palmas Drive Carlsbad, CA 92009-4859 BUREAU OF AERONAUTICS4100 DONALD DOUGLAS DR.90808 (213)421-8293 BUREAU OF ENGINEERING 333 W. OCEAN BLVD.90802 (213)590-6383 BUREAU OF PARKS2760 STUDEBAKER RD. 90815 (213)421-9431 BUREAU OF PUBLIC SERVICE 1601 SAN FRANCISCO AVE.90813 (213)432-8904 TABLE OF CONTENTS Page INTRODUCTION 1 BEACH LOCATION 2 NATURE OF THE PROBLEM 5 EAST BEACH HISTORY 7 RECENT INVESTIGATIONS AND MITIGATIVE ACTIONS 14 PROJECT FORMULATION AND DESCRIPTION 20 MONITORING PROGRAM 24 FIGURES 1. Southern California Coastline 2 2. San Pedro Bay 3 3. East Beach Vicinity 4 4. 1/19/43 Photo 8 5. 2/4/43 Photo 9 6. 4/54 Photo 10 7. 11/67 Photo 11 8. 2/79 Photo 12 9. 3/83 Photo 13 10. Project Schematic 25 11. Beach Sand Size Analyses 26 12. Seascape Placement Control Lines 27 APPENDIX (Bound Separately) A. Monitoring Results 10/83 B. Monitoring Results 4/84 C. Monitoring Results 10/84 NON-STRUCTURAL BEACH EROSION PROTECTION INTRODUCTION Beach erosion problems in the vicinity of 65th Place but extending ^ between 60th Place and 70th Place in Long Beach have troubled City government and many Long Beach residents over a period of several "* years. it What is now known as East Beach had retreated in 1979 to its ...« narrowest width in 35 years. The homes located on~the oceanfront could sustain severe damage if the narrow beach were to be totally '** removed by storm wave activity. A 60 year old timber bulkhead of uncertain integrity serves to support the foundation of the beach- front properties. In the event of severe erosion, that timber ,M bulkhead would be directly impacted by storm waves. It is doubtful that the bulkhead could prevent loss of foundation sand during any •«* significant wave or storm event. m Concern for the safety of beachfront homes coupled with a strong desire to reestablish a significant recreational opportunity has *"" led, since 1979, to a continuing and concerted effort to find *• suitable solutions. *» Consideration of measures to mitigate beach erosion was founded on the concept that any beach protection measures had to meet three fundamental objectives: 1. Allow a continuing recreational opportunity along ••* about 2,000 feet of beachfront. *"* 2. Provide a higher level of storm protection to ^ approximately 213 homes along the oceanfront which appeared to be subjected to increasing „ frequency of storm damage caused by high seas. •" 3. Reduce beach protection operating expenses of approximately $100,000 to $150,000 per year with "*" a majority of these operating expenses incurred — under urgency conditions. -1- BEACH LOCATION East Beach in Long Beach is located in Los Angeles County adjacent to the Orange County line. It is a southwesterly facing beach on the California coastline as shown in Figure 1. The Beach is par- tially protected by the Long Beach Breakwater completed by the Federal Government in 1949. A variety of man-made coastline modifi- cations have been installed over the years, the most notable of which, in addition to the Federal breakwater,are the extensive landfills of the Port of Long Beach, the oil islands in San Pedro Bay and the Alamitos Bay entrance channel jetty adjacent to the San Gabriel River and essentially on the boundary between Los Angeles County and Orange County. East Beach is shown in greater detail in Figures 2 and 3. It is on the San Pedro Bay side of the sandspit peninsula separating San Pedro Bay from Alamitos Bay. 120°W 119°W 118°W FIGURE 1 -2- w M m Copyright Automobile Club of Southern California. Reproduced by permission FIGURE 2 -3-BESTORIGINAll Island Chaffm 24 ARKER (l.fhual NATURE OF THE PROBLEM The eroding stretch of coastline in the vicinity of 65th Place is protected from extreme west and southwest weather by the offshore breakwater system of San Pedro Bay. There are thus only two pri- mary avenues of wave approach to the eroding area. The first is wave generation within San Pedro Bay Harbor by southwesterly winds in the Long Beach region. These waves are limited in height by the available windfetch between the breakwater and the shore- line. The longest southwest fetch across the Harbor extends from the west end of the Harbor to the eroding area in the vicinity of 65th Place. Within this maximum fetch, waves about four feet high can be generated under moderate wind conditions. The second avenue of wave approach permits storm waves from the open ocean to reach the beach at 65th Place. South storm waves or south swell penetrate through the gap between the eastern end of the Long Beach Breakwater and the Alamitos Bay entrance jetties. These storm waves are intensified by a diffraction effect which causes waves in the vicinity of 65th Place to be up to 10% higher than the offshore storm waves. The shore erosion that exists at East Beach is caused by a combina- tion of two distinct wave generated sand transport modes. The first is the rather mild but persistent long-shore sand transport generated by the prevailing southwesterly winds acting upon the water body within the enclosed harbor. Due to the longer fetch causing higher waves near 65th Place than farther westward, the rate of transport along the 65th Place beach is seven times greater than that occurring at Cherry Avenue three miles to the west. There appear to be seasonal changes in direction of this long-shore transport. The second mode of sand transport active along the eroded beach is the offshore movement of sand associated with the relatively infre- quent occurrence of large waves entering San Pedro Bay from the south through the breakwater gap. These periods of extreme erosion are well noted by the local residents and surpass in intensity the previously mentioned long-shore transport due to the low velocity prevailing westerly winds. The general movement of the eroded beach sand, once it is displaced from the beach, is to the east and offshore although some summer transport is toward the west. A bathymetric comparison between nautical charts of 1929 and 1976 shows a large volume of sediment that has accumulated at the west jetty of the Alamitos Bay entrance. In some locations, as much as 10 feet of material has accreted during the 48 years between the two surveys. Beach survey data compiled from City of Long Beach records has been helpful in estimating beach erosion rates since 1957. The period 1957 to 1978 has seen wide variations in beach width at -5- NATURE OF THE PROBLEM (Continued) "* m this location due to alternating periods of beach erosion and replenishment. However, during the same period, a rate of erosion „ of 5 to 10 feet per year was the trend over that section of beach between 59th Place and 72nd Place. During the period 1974 to *• 1976, when the character exhibited by the beach was described by local residents as "stable", a close examination shows an erosion "* rate approaching 2 to 7 feet per year over the same study reach. — Such a rate can be considered indicative of the persistent south- west wave activity. During the period 1976 to 1978, when extreme ^ storm wave erosion was seen, erosion rates averaged 40 to 50 feet per year. Recent survey data shows that the overall rate of erosion ** is a result of the rather mild persistent longshore transport events (1974 to 1976) and the high erosion rates of extreme storm wave * periods (1976 to 1978). «r Sand sizes in the East Beach area range from 0.07 mm to 2 mm in «• diameter with 50% of the grain sizes finer than 0.25 mm diameter. , These relatively finer grain sizes than other portions of the beach in Long Beach compound the erosion problem since this section of beach with smaller grain sizes has a greater exposure to storm * wave action than other sections of the coast line on San Pedro Bay. -6- EAST BEACH HISTORY The Alamitos Bay peninsula is the urbanized remnant of the sand- spit formed by riverine processes at the mouth of the San Gabriel River. In the natural environment, this river feature would be highly transient, both in shape and size, in response to the vary- ing conditions of river discharge, sediment load and incoming ocean wave energy. The first residents of the peninsula recognized the threat of potential flooding and constructed their homes on timber pilings to prevent inundation of their property during periods of high waves and tides. During the 1920's, residents sought to increase the stability of the peninsula by constructing a timber bulkhead to serve as a physical barrier from ocean forces. Their concern was sufficient to cause the timber bulkhead to be constructed by special assessment proceedings where the cost of the bulkhead was prorated to each of the benefited properties. At the time of bulkhead construction, the beach at the base of the 15-foot high wall was quite narrow. During periods of high tide, ocean waves impacted the structure directly. Old pictures of the timber bulkhead, as it existed in 1943, show what appears to be a combination of armor rock and concrete rubble at the base of the bulkhead. These same photographs show successive pictures during a two-week period in early 1943 at zero tide where there appears to have been a loss of sufficient sand to lower beach levels at the wall by about eight feet. In the late 1920's, construction of the Long Beach Breakwater began. Incoming wave energy was reduced to the present relatively protected condition. Structural protection provided by the break- water served for approximately 20 years. After World War II, a beach of significant width was placed on the ocean side of the bulkhead. The beach was formed from 3 million cubic yards of fill material provided by dredging of Alamitos Bay. Within a few years of placement of the artificial beach, the coast in the vicinity of 65th Place began to erode at a greater rate than the beaches immediately east or west. To combat the erosion, 200-foot long timber groins were constructed normal to the shore- line. The groins were permeable and did not effectively stabilize what is now known as East Beach. Following demonstration of the ineffectiveness of the timber groins, the strategy for beach pro- tection in the ensuing 30 years was periodic beach renourishment from dredging activity in Alamitos Bay, the Alamitos Bay Entrance Channel and the mouth of the San Gabriel river. -7- Om 00 DATE: JANUARY 19, 1943 TIME: 3:08 P.M.) TIDE: 0.0 AT STATION 245f50, 55th PLACE, 180 FEET SOUTH OF BASE LINI LOOKING EAST., FIGURE 4 Qm CD DATE: FEBRUARY 4, 1943 TIME: 3:28 P.M.) TIDE: -0.1 !' AT STATION 245*50, 55th PLAGE, 160 FEET SOUTH OF BASE-LINE LOOKING EAST.i FIGURE 5 om FIGURE 6 ^*«t-"-w .. "gp»aaj ^^m "-RvC"., * ,f**^% UJcc3o PAGE 11 CO Ul<r o LL PAGE 12 PAGE 13 RECENT INVESTIGATIONS AND MITIGATIVE ACTIONS Following the 1978-79 winter, it became apparent that new strategies would have to be devised for beach protection activity if these activities were to be perceived as effective measures for protect- ing peninsula homes and for continuing the recreational oppor- tunity at East Beach. Constant disruption of the beach, due to dredging activity, was clearly disruptive of recreational oppor- tunities and available funds at the time did not permit placement of enough sand each time to produce any feeling of reassurance regarding those replenishment activities. Consultants were retained by the City in an attempt to identify more definitively the causes of erosion at East Beach and to suggest both short-term and long-term mitigation strategies which would permit a more orderly approach and progress toward long-term beach protection measures. Available fill for beach replenishment on a short-term basis existed in the mouth of the San Gabriel river. This material ranged in grain size from 0.09 mm to 0.4 mm in size with 50% of the San Gabriel river borrow site containing grain sizes of less than 0.16 mm. It was clear that the San Gabriel river fill material was considerably finer in size than the material originally placed on the beach. Other existing beach sand at Cherry Avenue in Long Beach was investigated as a potential borrow area because of the great width at that point. However, the Cherry Avenue beach material was 50% finer than 0.22 mm in grain size and was still finer than the material in place. Investigations in evaluating the stability of both sources of sand concluded that neither was well suited for beach replenishment and that the beach that could be constructed from either of these two materials would be less stable than the beach constructed in the late 1940's. A number of alternative mitigative actions were identified in the October 1979 report of the consultants. These alternatives included: 1. Beach replenishment with coarser sediments. 2. Installation of a filled groin field. 3. Installation of a shore parallel breakwater. 4. Construction of a dogleg westerly extension of Alamitos Bay jetty. 5. Installation of the Alamitos Bay jetty extension together with breakwater additions on the Chaffee and Freeman oil production islands. 6. Easterly extension of the Federal breakwater into Orange County to shield this section of East Beach from southerly storm swells. -14- RECENT INVESTIGATIONS AND MITIGATIVE ACTIONS (Cont*d) Costs of traditional breakwater installations of any type exceeded funds available and the time period to secure sufficient funds was clearly too long to be responsive to the problem which already existed following the 1979 storm erosion events. As a result, a short-term mitigative action was selected, coupled with a decision to investigate longer term strategies in more detail and with greater care before making a decision on longer term beach erosion protection measures. Available funds permitted consideration only of two of the alterna- tives identified above. The alternative of installing a filled groin field was not well received because of significant impact on the recreational quality which could be provided on the resulting beach. The filled groin field alternative would have restored the beach to a 100-ft. width and then shore perpendicular sheet-pile groins would be installed to provide shelter from wave attack and lessen the velocity of longshore currents that could strip the sand from the beach face. Four 200-ft. long impermeable groins would be placed with the expectation that the erosion rate could decrease thereby to 25% of the present erosion rate. Because of the poor reception to the filled groin field and the detrimental impact on recreational quality, the short-term miti- gative action chosen was beach replenishment from the San Gabriel River borrow area coupled with installation of coarser grain sizes imported overland to East Beach since coarser sediment locations in San Pedro Bay were unknown. The alternative anticipated that the use of the "bird's-eye" coarse grained sand backed up by San Gabriel River borrow would increase beach sand resident time. "Bird's-eye" fine gravel was essentially a quarry waste material which could be acquired at reasonable cost. Compared to the existing sand on the beach an ocean-face dike of such material would provide exceptionally high stability while still not being so coarse as to significantly degrade recreational quality. The resulting coarse sand face could stand on a steeper slope and thus decrease the total amount of imported material to East Beach. During discussions of the proposed short-term beach protection pro- ject, consideration was actually given to replacement of the timber bulkhead of uncertain integrity with a concrete seawall in a gravity section. Such a project, however, would have its costs assessed against the homeowners and the costs were reported as in excess of $400 per foot of wal1. During these 1979-80 discussions regarding East Beach, a Local Coastal Program was proposed and ultimately adopted for Long Beach. In that Local Coastal Program there were provisions concerning beach width, beach sand and control of beach sand and width. The Local Coastal Program called for all beaches in Long Beach to be maintained at widths which were equal to the actual width during the month of August for the years 1973 to 1978 or 150 feet, whichever was greater. The quality of sand utilized to maintain the beach surface area was required to be at least equal in quality for -15- RECENT INVESTIGATIONS AND MITIGATIVE ACTIONS (Cont'd) aesthetic and recreational purposes to the general sand quality existing during the year 1978. A control system was required for monitoring beach sand and width. With the selection of the coarse sand and beach fill alternative, a more-detailed assessment of expected beach fill behavior was performed during the summer of 1980. Tetra Tech, Inc., the con- sultants who provided the original survey report, also performed the assessment of expected beach fill behavior. Tetra Tech reported that although it was not possible to accurately estimate an expected "life" for the proposed beach fill, the project should be considered a sound investment in beach protection. It was stated that the coarse-grained material would be more stable in every case than the existing beach material. Given the potential for storms, the state of the existing beach and local concerns, it was concluded that the protection provided by coarse-grained fill would be warranted. Tetra Tech also strongly recommended a program of inspection and monitoring of the beach fill as being essential to the establish- ment of an adequate and cost-effective maintenance program which would inevitably be required with such a strategy. Compilation of near shore wave statistics, evaluation of the expected beach behavior and an assessment of the project effectiveness, life and maintenance were investigated and effectively confirmed, with minor modifications but with much greater precision, the conclusions contained in the 1979 report on the causes of beach erosion. A summary of the near shore wave conditions at the beach fill site and their relationship to the existing erosion processes follows: 1. Locally generated wind waves with typical heights 2 to 2.5 feet and periods of 3 to 5 seconds predominate from the southwest causing eastward sediment movement from the project site. 2. Local ocean sea outside the breakwater with heights normally ranging from 3 to 5 feet and periods between 4 and 8 seconds often penetrate through the gap between the easterly end of Long Beach Breakwater and the Alamitos Bay entrance channel and impinge on the East Beach shoreline causing offshore transport and poten- tially some westward sediment transport from the project site. No recent data could be obtained within the scope of the assessment study to identify any intensification of these waves within the past few years. However, it was concluded that the intensification would seem likely noting the recent higher frequency of winds from the southerly quadrant measured at shore stations. -16- RECENT INVESTIGATIONS AND MITIGATIVE ACTIONS (Cont*d) 3. Southern ocean swell from distant storm events also intrude into the bay and directly impact the site with heights typically 1 to 2 feet and periods of 13 to 20 seconds, causing poten- tially some westward sediment transport from the project site. No recent data were avail- able within the scope of the study to identify any intensification of these waves over the past few years. Consultants concluded that a different beach behavior could be expected as a result of the placement of the coarse-grained sand material on the existing fine sand beach. It was recognized that design of beach fills is largely empirical methodology. No directly comparable projects to the one proposed were known although there was some applicable experience and experimental work available. On a judgment basis, despite the lack of comparable projects, it was concluded that there was no question that a substantial increase in grain size on a beach would result in added stability. In summary, it was concluded that the long-term response of the coarse fill to storm activity could be expected to be much the same as the response of the existing beach to storms. The difference between the existing and coarse beach material would lie in the higher intensity of wave conditions required to cause these beach changes. It was lastly concluded that all indications from the investigations were that the coarse grained material proposed for use would retard East Beach erosion greatly relative to the existing beach material whatever the future wave climate might be. "Pebble Beach" was installed during the fall of 1980. The coarse- sand dike and blanket was breached by 1980-81 winter storms. Except for the problem of breaching due to wave overtopping, however, the remainder of the protected beach performed well during 1980-81. During the subsequent summer season, breached areas were rudimen- tarily repaired through installation of additional coarse-grained material. Some migration during the 1981 summer season was noted to the east and to the west along the beach as well as offshore. It is uncertain whether the offshore migration was due to the breaching activity due to overtopping. The coarse-sand dike and blanket was further damaged by maintenance activity. Beach cleaning, with mechanized equipment, tended to mix the "bird's-eye" with the finer beach sands. Natural sorting actions continued along with continued remixing from beach cleaning activities. The "bird's-eye" dike, therefore, tended to break down due to fair weather recreational maintenance efforts. Further breakdown of the "bird's-eye" dike and blanket occurred during high tide storm events. Bulldozer activities to construct traditional sand berms along East Beach further contaminated the "bird's-eye" resulting in even further lessened effectiveness. By 1983 it was clearly time for serious consideration of longer term beach protection solutions which were less susceptible to equipment caused damage. -17- RECENT INVESTIGATIONS AND MITIGATIVE ACTIONS (Cont'd) Following installation of the short-term beach protection with coarse-grained material, more detailed investigations of longer term protection measures were engaged. A total of nine alternative beach protection measures were analyzed to determine their effectiveness and acceptability in reducing erosion at the project location. Of the nine alternatives, two relied upon artificially adding sand to the beach; three alterna- tives used some type of beach structure to retard sand losses; and the remaining four alternatives involved various offshore structures that act to reduce erosional wave forces upon the beach. The functional, economic and environmental characteristics of each alternative were compared against specific project goals and con- straints. The relative capabilities of the various shore protection measures were then determined through a preliminary screening and final selection procedure. An analysis of the nine shoreline protection measures demonstrated that placement of groins, seawalls or other structures upon the beach to retard erosion were clearly not preferred for the East Beach project. These alternatives generally exhibited excessive maintenance costs and produced noticeably adverse impacts upon recreational beach usage and aesthetic qualities. Alternatives of periodic beach replenishment or massive sand filling were regarded as objectionable for the same reasons. Also, of all of the beach structure and beach fill alternatives, only the seawall possessed good functional characteristics of adequate wave protection. A scheme to extend the Alamitos Bay west jetty was rejected on the basis of excessive construction costs and functional ability. Offshore structures that dissipate wave energy, thereby reducing erosional conditions at the shoreline, were thus favored over other protection methods. These offshore structures have clearly demon- strated their functional capability over the long term in countless applications and were perceived as being able to avoid unacceptable impact upon social and biological values. Their danger to naviga- tion could be mitigated by navigational lights and buoys. During the final selection, four offshore alternatives were analyzed but two of them (segmented rock reef and submerged rock reef) were combined into one alternative because of their structural and functional similarity. The rock reef concept was determined to have lower costs, greater design flexibility and better effectiveness than the other remaining alternatives of pile row barriers and sheet pile barriers. The estimated cost of an offshore shore parallel rock reef with a crest height near mean tide level was estimated to cost approximately $2,000,000 and it was concluded that it could be relied upon to substantially reduce long term shore recession rates at East Beach. -18- RECENT INVESTIGATIONS AND MITIGATIVE ACTIONS (Cont*d) A potential cost in excess of $2,000,000, however, exceeded avail- able local funds by at least $1,000,000. Once again, the deteri- orating condition of East Beach introduced an element of urgency for a longer term solution which could be implemented without the time-consuming undertaking of searching for additional funds from other agencies. Re-analysis was clearly indicated with that re- analysis to include serious consideration once again of perhaps less traditional protection techniques and preferably of a non-structural nature. Original goals for East Beach were confirmed. A beach reestablish- ment/stabilization solution was needed which would: 1. Allow a continuing recreational opportunity along about one-half mile of beach without significant impairment. 2. Provide a higher level of protection to ocean-front homes from about 60th Place to 70th Place. 3. Reduce beach protection operating expenses of $100,000 to $150,000 per year which are inevitably accompanied by severe overtime demands on City forces. Constraints on achieving such goals were explicitly identified. They included: 1. Significant federal or state funds are highly unlikely to be available in the near term. 2. Long-term availability of local funds is un- likely because of the City of Long Beach's diminishing share of Tidelands Oil Revenue Funds. 3. A declining willingness to accept continuing significant uncertainty regarding East Beach erosion protection solutions. Given the goals and the constraints, a long-term solution to the problem of East Beach inevitably drove a search for that solution away from traditional coastal engineering measures and toward non- structural measures such as diminishing tractive forces on the underwater fores!ope of the beach and attempting to find some tools which would utilize natural coastal forces to the benefit of East Beach rather than allowing those natural forces to continue to erode the beach. -19- PROJECT FORMULATION AND DESCRIPTION Newspaper publicity concerning beach erosion protection investiga- tions by the City and public reaction thereto produced contact by the manufacturers of "Seascape" with the suggestion that this new concepT~fo?~the control of beach erosion should be seriously con- sidered for use in controlling shoreline erosion at East Beach. "Seascape" is essentially a synthetic seaweed which, when properly positioned offshore, functions somewhat as an underwater snow fence by slowing bottom currents to precipitate heavier suspended sedi- ments. Clusters of the units were claimed to be effective as sand catchers as long as sand was suspended in the water. The use of "Seascape" at Cape Hatteras, North Carolina, was cited as a success- ful installation which provided a net accretion in the beach profile during the summer months of 1981. "Seascape" is a product constructed of a textile fiber material called Typar, manufactured by the DuPont Company. It has been used extensively for carpet backing and in road support fabrics. This "Seascape" erosion control device is approximately 5-ft. long and consists of a hollow anchor portion with 4-ft. long fronds attached throughout its length. The anchor tube is partially filled with sand to hold it on the bottom. Flotation devices sewn into the fronds enable them to float upward from the sand-filled tube. The purpose of the unit is to trap sand offshore in much the same manner that snow fences trap snow to, thereby, form a reef. Public Works staff investigations indicated that there was indeed beach accretion at the Cape Hatteras National Seashore in the vicin- ity of the lighthouse following installation of an experimental section of "Seascape" in 1981. Definitive data, however, was not available although a qualitative approach (based on telephone inter- views) in considering the Cape Hatteras installation would produce a tentative conclusion that "Seascape" is, at the very least, a contributor to the desired beach accretion. "Seascape" has also been utilized in several installations in the Great Lakes. Contact with the Wilmette Park District indicates the potentials for rather spectacular success not only in erosion protection but in beach accretion. Officials of the Wilmette Park District were enthusiastic concerning the use of artificial seaweed for shoreline protection. Once again, however, controlled experi- ments were not made and it appeared that use of the synthetic sea- weed was influenced by a "last resort" situation. Some concern was expressed regarding abrasion resistance of the Typar material and its flotation capabilities. The existence of suspended sand close to the bottom offshore from East Beach in approximately 6 to 8 feet of water at mean lower low water was confirmed by Long Beach lifeguard divers. Small amounts of sand were found in grab samples about 1 foot above the bottom on a calm day. -20- PROJECT FORMULATION AND DESCRIPTION (Cont'd) Sand sizes at Cape Hatteras were compared to sand sizes at East Beach. A grab sample of Cape Hatteras sand indicates grain sizes ranging from 0.15 to 1.4 mm with 50% of the grain sizes in the grab sample finer than 0.35 mm. It appears that the Cape Hatteras sand is of a more uniform gradation than that found at East Beach but is somewhat larger in median size. The 50% finer size at 67th Place is 0.25 mm. The 50% finer size at Laguna Place is 0.32 mm. (See Figure 11 for a comparison of sand sizes.) Flotation capability of "Seascape" fronds was rough checked by Long Beach Lifeguards. A unit was placed in the water at approxi- mately elevation -6.0 (MLLW). After two weeks, fronds were still floating upright with no evidence of fine silts clogging pores of flotation devices or the Typar fabric. It was reported that there appeared to be some preliminary buildup of bottom around the anchor tube. The basic design concepts for the current East Beach Erosion Pro- tection Project are: 1. Reduction of shore normal tractive forces. 2. Use of natural physical processes. Using these basic design concepts, the East Beach Project consists of two elements which will: 1. Place dredged sand from San Pedro Bay onto the foreslope of East Beach to flatten beach slope in the breaker zone from the present 7 to 9 feet per 100 feet to 3 feet per 100 feet. Bed load tractive forces would be proportionately reduced and the resulting "water cushion" would reduce the tendency of wave energy to cause the relatively fine existing sand to go into temporary suspension and the associated offshore sand movement. 2. Place an experimental field of artificial (synthetic) kelp in a shore parallel orientation in 6 to 8 feet of water (MLLW) to act as an underwater "snow fence" and inhibit bed load and suspended sediment transport out of the area. Estimated cost of the project is approximately $950,000. Of this amount $57,500 is for the furnishing of "Seascape". A total of $781,000 is for placement of dredged fill from San Pedro Bay onto East Beach and the foreslope of it out to approximately minus 8 feet (MLLW). -21- PROJECT FORMULATION AND DESCRIPTION (Cont'd) Necessary permits have been secured for the project from the Corps of Engineers, the California Lands Commission and from the Cali- fornia Coastal Commission. Construction contracts have been awarded. Scheduling for the dredg- ing project calls for it to be fully completed by April 1, 1983. Fifteen hundred units of "Seascape" have been delivered. They will be installed on a time-available basis by Long Beach lifeguards as soon as the dredging project has been completed. Final "Seascape" placement investigations have been concluded by Beach Builders of California, the supplier of the artificial kelp. In addition to the bottom current identified in previous reports, the issue of downwind turbulence from the oil islands in San Pedro Bay inducing an additional vector of bottom currents has also been identified. It was also pointed out that periodic offshore winds from the west and northwest would induce currents which reflect off of the Long Beach breakwater and directly impinge on this section of East Beach. The consulting geologist for Beach Builders of California has recommended three continuous rows placed 10 feet apart with the middle row of "Seascape" placed at elevation -6.0 (MLLW). Given the foreslope of the beach in this area, the near shore row would be at approximately elevation -5.0 (MLLW) and the outer row would be placed at approximately elevation -6.5 (MLLW). The installation will cover the beach shoreline between 59th Place and 71st Place... a distance of roughly 2150 feet. In addition, Beach Builders of California has supplied, as a further experiment, a heavy plastic curtain version of "Seascape". This plastic curtain is approxi- mately 3 feet long with a sand filled anchor tube at one end and flotation spheres approximately the size of ping-pong balls secured in the other end of the plastic curtain. The plastic experimental section will be installed in a fourth row toward the sea at an elevation of approximately -7.0 (MLLW) opposite those sections of East Beach which have exhibited the most severe erosion effects and in a former bottom valley. The plastic units will be installed at approximately 3 foot centers in the fourth row and should cover that portion of the beachfront almost between 64th Place and 66th Place. The reason for the added experimental installation of the plastic curtain units is the discovery by the consulting geologist that there were some significant valleys in the bottom contours where it could be expected that velocities might be higher due to the general configuration of the shorelines and structures in San Pedro Bay. -22- PROJECT FORMULATION AND DESCRIPTION (Cont'd) Lifeguards of the Long Beach Marine Bureau have been considering how best to install the "Seascape" units in a reasonably efficient system in order to expedite the project's experiment. While dropping test units off of the lifeguard rescue boat, divers were immediately disoriented as to which direction the unit should be placed. They also had difficulty in locating the "Seascape" unit again once it was placed on the bottom. They propose to use a line with appropriate markings so that each unit can be properly spaced. This line would have weights on each end to properly secure it to the bottom. Attached to each weight would be a surface marker buoy. The length of the line would be about 50 feet and would be marked with tape. The weights are planned to be heavy enough to hold the line in place but light enough for a diver to lift and swim through the water. Weights used by the divers for grid pattern searches are contemplated. Once the kelp units are placed along the 50 foot line, a diver could pick up one end and swim it over the other end which would stay in position and place the weight and buoy so that the correct line could be maintained. This flipping of the line would be1 done along the entire length of the predetermined course. With two divers assigned to each line, several rows can be placed at the same time. Kelp units would be shuttled to the divers from the barge by rescue boards, dories, maintenance whalers, or any other easily maneuvered vessel. They believe that such a plan will help the project move quickly and efficiently. -23- MONITORING PROGRAM The City has learned, by its recent experiences, that a monitoring program producing relevant data is essential to accumulating empiri- cal knowledge in coastal engineering. Conditions of permits also require a comprehensive monitoring program. The monitoring program consists of: 1. A minimum of at least 3 profile range lines will be established along the 2800 foot project site. Permanent benchmarks are located in the project area and will be used to survey the range lines vertically. Two additional range lines will be established with one at each end of the Seascape area and far enough away from any of its influence but close enough to be in the same beach and wave environment. These range lines will also be surveyed. Range lines will extend from estab- lished beach to beyond 10 feet below MLLW. After the fill is emplaced an initial beach configuration baseline will be established and surveyed. 2. Beach profiles along the range lines will be measured at selected times at least twice a year. Profiles will then be compared for systematic differences in the test and end areas. 3. Daily wave observations will be compiled in the area. 4. All related monitoring data will be published. Results of the monitoring program are included in the separate Appendix to this report. In addition, efforts will continue to incorporate the ocean/bay beach front of Long Beach as a part of the Corps of Engineers' Beach Erosion Control Project which now extends from Anaheim Bay to Newport Bay. -24- • i t i t i t li i t i i li it ti t i ti ti if t * * * •a *-j i" EAST BEA.'CH ST ABILI-Z ATION PROJECT BEST ORIGINAL FIGURE 10 • i II if t I il ti I* it II II II KACH &ACH SANDS GRAIN SIZE vs. % PASSING t ! !• FIGURE 11 BEST ORIGINAL 6UOY, TYPICM. WEIGHT, \0 TYPICAL. 0 TO SUIT TIDE , t> TO I1-FEE.T 1/4" UWE y VtLLOW ^\ TYPICAL 0 FIR'ST ROW EL -^. THIRD ROW -*r PL^CEM^HT COMTROL LIMES ;: i" = 10 FIGURE 12