Loading...
HomeMy WebLinkAbout; Carlsbad Beach Erosion Study-Shore Protection; Carlsbad Beach Erosion Study-Shore Protection; 1989-04-01CITY OF CARLSBAD PROPOSAL FOR THE CARLSBAD BEACH EROSION STUDY AND COASTAL SHORE PROTECTION PROJECT APRIL, 1989 CITY OF CARLSBAD PROPOSAL FOR THE CARLSBAD BEACH EROSION STUDY AND COASTAL SHORE PROTECTION PROJECT APRIL, 1989 CLAUDE A. LEWIS, MAYOR ANN J. KULCHIN, MAYOR PRO-TEM MARK V. PETTINE, COUNCILMEMBER JOHN J. MAMAUX, COUNCILMEMBER ERIC LARSON, COUNCILMEMBER RAYMOND R. PATCHETT, CITY MANAGER JOHN J. CAHILL, MUNICIPAL PROJECTS MANAGER CARLSBAD CITY HALL 1200 ELM AVENUE CARLSBAD, CALIFORNIA 92008 (619) 434-2830 CITY OF CARLSBAD PROPOSAL FOR THE CARLSBAD BEACH EROSION STUDY AND COASTAL SHORE PROTECTION PROJECT APRIL, 1989 INTRODUCTION The City of Carlsbad is a Southern California coastal community of approximately 60,000 residents located in Northern San Diego County. Carlsbad is bounded on the west by approximately six and one half (6.5) miles of ocean front in which it shares its presence with a combination of properties and facilities owned and operated by the State of California, the San Diego Gas and Electric Company, and the Regional Encina Sewage Treatment Facility. Three (3) major coastal lagoons are located in Carlsbad: Buena Vista Lagoon on the north, Agua Hedionda Lagoon, and Batiquitos Lagoon on the south. Carlsbad has three (3) major north-south thoroughfares which serve the entire Northern San Diego County region's circulation system: Carlsbad Boulevard, a portion of U.S. Highway 101, Interstate 5, and El Camino Real. Reference Figure 1. CITY OF CARLSBAD OCEANSIDE TO SAN OIEGO 40 MILES ENCINITAS FIGURE 1 The Southern California coastline experienced severe damage from Winter storms in 1983. Carlsbad's beaches have yet to recover. What little sand that existed at the time, and later followed by other Winter storms, has been removed, and to date not returned to the beaches. In January of 1988, a Winter storm struck the Southern California coast resulting in millions of dollars of property damages area wide. In Carlsbad, this storm damaged important public parking facilities, resulted in road closures and required extensive and costly maintenance and clean-up. Carlsbad is dangerously and repeatedly exposed to severe and expensive damage to private property and important public transportation and circulation systems. The United States Army Corps of Engineers sponsors two (2) programs that are specifically designed to provide both short term and long term assistance to both the City and the general public in our area. CORPS PROGRAM SUMMARIES The City of Carlsbad has formally requested support from the United States Army Corps of Engineers under their "continuing authority" for the Corps' Los Angeles District Office to initiate a Section 103 "Small Beach Erosion Control Project" to assist the City investigate alternatives protecting a section of Carlsbad Boulevard from repeated damage. Secondly, the City has formally requested inclusion in the next available United States Army Corps of Engineers' budget, authorization for the Corps to begin a study of the causes, effects, and solution options to the severe beach erosion problem in the City of Carlsbad. The first step towards such a study can be accomplished by the addition and/or inclusion to the Corps' budget authorization and funding appropriations in the amount of $250,000 specifically earmarked for the Carlsbad Beach Erosion Study. SECTION 103 "SMALL PROJECT" PROGRAM INTRODUCTION The proposed project area generally covers the shoreline from the south end of the existing SDG&E jetties at the entrance to Agua Hedionda Lagoon to the north end of the SDG&E outlet jetties. The subject portion of Carlsbad Boulevard where the shore protection is proposed is approximately 2,600 feet long and is situated along the beach. Carlsbad Boulevard drops down to its lowest level through this area where the elevations along the existing street center line range from approximately +13 to +16 feet, mean sea level datum (MSLD). Reference Figure 2. The existing roadway along this area is approximately 40 feet wide with parking for automobiles along the west side of the SCALE: 1" = 2000' LOCATION MAP CARLSBAD BOULEVARD SHORE PROTECTION FIGURE 2 —, DRAWNBY: cb | CHECKED BY-/A< | PROJECT NO; 8851268E-SI01 | P*TE: 7-28-88 | WOODWARD-CLYDE CONSULTANTS Boulevard. The parking area is separated from the roadway by an asphalt berm and abuts directly against the beach. For several miles, Carlsbad Boulevard runs parallel with, and adjacent to, the beach and is the primary access to several residential areas, commercial centers, regional power generating facilities, and related business and transportation interests. This section of Carlsbad Boulevard is also the only roadway west of Interstate 5 to cross Agua Hedionda Lagoon. As such, it carries the majority of north-south traffic through the area. The beach in this area is historically thin and narrow. Almost every year, Winter storms strip away the thin layer of sand from the Summer swells and sand transport leaving a discontinuous layer of gravel and cobbles. During the most severe Winter storms, large waves impact directly on and overtop Carlsbad Boulevard in this area. Because of the proximity of the ocean, the highway is washed out. In the latest major storm of January 17 and 18, 1988, important public parking facilities along the west side of the road were lost and the slopes that support the roadway were severely eroded. Reference Figure 3. The paved parking area has been reduced from approximately 300 spaces to about 60 spaces. Neither the City of Carlsbad nor the State of California, Department of Parks and Recreation, has the funds to properly maintain this area on an annual basis. In fact, repairs that have been made at substantial City expense, have been damaged again or completely destroyed. Because of the vital importance of this roadway to the regional circulation system of both the City and the northern portion of the County, the City of Carlsbad will begin widening and improving Carlsbad Boulevard within the subject area immediately. These improvements, at a cost of approximately $2,500,000, include a divided roadway with a raised landscaped median, parallel parking on the west side, and pedestrian walkways on both sides. New landscaping and safety lighting are also planned. In order to protect these improvements, the City requests the assistance of the United States Army Corps of Engineers to investigate alternatives and assist with the financing of a permanent solution to protecting this important public thoroughfare at the earliest possible time. The City has undertaken a preliminary feasibility study to investigate potential alternatives to construct some type of shore protection. Ten (10) different structural considerations were reviewed. Based upon civil and coastal engineering review, the City has identified several potential alternatives. One approach is an anchored sheet pile wall with a concrete cap which has the advantage of impacting the least amount of beach while at the same time providing the most stable, long term structural life. Reference Figure 4. The City requests Corps participation in any approach to a permanent solution to this situation. Reinforced Concrete Cap +14.0 -20 FIGURE 4 Other considerations for a shore protection project for this section of Carlsbad Boulevard include the necessity of placing rip rap material north and south of the proposed wall. Additionally, handicap access to the beach areas in the form of ramps and short stairways has long been a primary concern to the community. Reference Figure 5. The alternative to constructing a proposed shore protection project along the subject portion of Carlsbad Boulevard is, essentially, to do nothing in which case continued erosion and damage to the roadway would occur during frequent periods of high tides and Winter storms. This would result in continued high maintenance costs for the area, damage, and repair costs to the new improvements as well as replacement costs for portions of the roadway and existing utilities. This approach does not appear to be consistent with the current and pro j ected use of the area. Additionally, some permanent method* of protecting coastal resources and regionally strategic public highways is fundamentally important to all. Several other approaches are also possible alternatives such as beach nourishment or off-shore protection. These measures include possible revetments, groin systems, sand fills, breakwaters, and a permanent sand by-pass system. Only the sand Aqua Hedionda Lagoon Handicap Ramp Approx. Center line of Road Handicap Ramp. Indicates approximate location of test boring Indicates approximate location of survey profile line. .Plan is a portion of "County of San Diego - Topographic Ma'1 dated 9^17-75 - USC&GS 1929 see level datum Pacific Ocean SITE PLAN CARLSBAD BOULEVARD SHORE PROTECTION WOODWARD-CLYDE CONSULTANTS fill program has been attempted to date and was only temporarily successful. A sand by-pass system is currently under construction by the United States Army Corps of Engineers for the Oceanside Harbor entrance in an attempt to reduce maintenance dredging and provide a continuous sand replenishment system. Even if successful, it will be several years before the results of this program for the Oceanside Harbor can be evaluated. As of this date, continued funding for the construction, development, operation, maintenance, and monitoring of the Oceanside Harbor Sand By-pass Project by the United States Army Corps of Engineers is in doubt. It is clear that Carlsbad's erosion problems are affected, if not directly caused by, sources outside of its own jurisdiction and beyond Carlsbad's capability to resolve. Other measures must be sought to provide long term solutions. Since it is both impractical and not cost effective to close or relocate the highway, some method of protecting it over the long term needs to be identified and funded. The City believes that the United States Army Corps of Engineers can provide the assistance and funding necessary to insure continued public and private benefits which this highway serves. Under the Corps' continuing authority through a Section 103 project, such important public facilities as transportation and circulation systems can be protected from increasing and continuing damage. The City of Carlsbad believes there is substantial federal interest to necessitate the United States Army Corps of Engineers' involvement in a proposed shore protection project for this area. Such a partnership between the City and the Corps will go a long way to protecting and promoting the local and national interests while insuring quick resolution to a long standing problem continually threatening the public's general welfare. ECONOMIC CONSIDERATIONS The proposed shore protection project would extend approximately 2,200 feet along the shoreline. In addition, it is estimated that the existing rock revetments for approximately 250 feet in length at both the north and south end would need to be replenished and/or repaired. The following is an estimated construction cost in 1989 dollars: Construction $2,720,000 Construction Contingency (15%) 408.000 Total Estimated Construction Costs: $3,128,000 Engineering and Design $ 100,000 Supervision and Construction Administration 100.OOP TOTAL ESTIMATED PROJECT COST: $3,328,000 BENEFITS ESTIMATE Benefits are calculated comparing the existing facilities, the proposed improvements to Carlsbad Boulevard, and area use to the probable conditions, repairs, and required maintenance. This assumes that no protection is provided for the proposed new improvements on the Boulevard and that the erosion and corresponding damage continues to occur, as it has historically been demonstrated, on a periodic basis. It is anticipated that a loss of benefits will occur every two to three years and will last until they are restored by repair and maintenance. The loss of benefits includes temporary loss of parking area and public beach access; temporary closure of the road resulting in detour of north-south vehicle traffic; temporary loss of bicycle travel lanes; temporary loss of public utilities; and reduced tourist use of the area. The value of these benefits is estimated from the value of lost time and the cost for repairs and maintenance. For estimating purposes, the following assumptions are made: A 50 year useful life for the project; Major damage due to storms once in 5 years; Minor damage due to storms twice in 5 years; An average beach use of 3,000 persons per day; An average future daily traffic volume for Carlsbad Boulevard of 27,000 trips per day; An average daily bicycle traffic volume of 200 trips per day; and Gas, water, electric, storm drain, and other important public utilities destroyed once in 50 years. Based upon these assumptions and historical data for this area, the following is the average annual value of benefits lost per year; Improvement Replacement/Maintenance Costs $ 47,000 Beach User Benefits Lost 81,000 Bicycle Lane Use Lost 14,400 Vehicle Operating Cost on Detour 162,000 Lost Time Value on Detour 115,715 Utility Replacement Costs 36,126 Other Miscellaneous Losses 50,000 TOTAL ANNUAL BENEFITS LOST $506,241 BENEFIT/COST RATIO For the purposes of this estimate, construction costs are spread over the estimated 50 year useful life of the project at an interest rate of 12% and added to the annual estimated maintenance cost of $3,600. The annualized construction cost is, therefore, determined by multiplying the total cost by 0.12082. Annualized Construction Cost: $3,128,000 x 0.12042 = $376,675 Annual Maintenance Cost 3.600 TOTAL ANNUAL COST $380,275 The total annual cost compared to the total annual benefits lost yields a benefit/cost ratio of approximately: Benefit Cost Ratio: $506.241 = 1.33 $380,275 CONCLUSION The City of Carlsbad believes there is substantial federal interest involved necessitating the request for United States Army Corps of Engineers' involvement in a Section 103 "Small Project" for a shore protection approach to protecting Carlsbad Boulevard. The City respectfully requests the Corps' involvement from an engineering and financial standpoint, in a potential solution to protecting the roadway at the earliest opportunity. CARLSBAD BEACH EROSION STUDY INTRODUCTION The January, 1988 storms, because of the lack of sand on the beaches of Carlsbad, caused severe damage to both public and private property. This situation is historical; storm data for the last three (3) decades indicates a direct relationship between Winter storms accompanied by high tides resulting in corresponding coastal damage. Private property in Carlsbad has been continually threatened and damaged by the regular cycle of Winter storms. Reference Figure 6. Public facilities including important beach parking lots have been continually inundated during Winter storm periods resulting in severe damage and expensive repairs. A public parking facility north of the Agua Hedionda Lagoon Bridge in Carlsbad suffered severe damage including a breach of the existing rock revetment. Reference Figure 7. ^~I B FIGURE . •I p *'jr•»$? -v<-^£- *~*-*+**• ^ * - r *\'"S- '^ > *:4A > . -^' FIGURE 7 Sections of Carlsbad Boulevard, a portion of U.S. Highway 101, are temporarily closed to traffic during Winter storms. City maintenance crews repeatedly clean-up the coast highway and repair damage to roadway sections. Public safety vehicles, including emergency responses, are temporarily and critically rerouted to avoid the closed highway. Costs to the City, inconvenience to the general public, interruption of public services, and the economic impacts caused by severe Winter storms in Carlsbad continue to tax local public financial resources. Reference Figure 8. Figure 9 below identifies the several public facilities and private homes in the immediate area of Winter storm impacts. BUENA VISTA LAGOON REGIONAL SHOPPING CENTER PRIVATE HOMES BRIDGE PRIVATE HOMES? BRIDGE STATE CAMPGROUND DUAL BRIDGES FUTURE STATE BEACH PARKING LOT S.D.G.4 E. POWER PLANT FIGURE 9 I/ FIGURE 8 SUSPECTED BEACH EROSION CONTRIBUTORS Beaches and sand dunes are the best dissipators of wave energy. A wide, sandy beach provides a sufficient buffer between the storm wave and backshore properties and facilities. After the erosion caused by the storm, the beach will generally regain its pre-storm width during periods of mild wave activity; that is, only if there is sufficient sand to naturally nourish the profile. The beach in a sediment start area such as in the City of Carlsbad, lacks this self-rejuvenating mechanism. The beach in a sand starved area also is a poor wave energy dissipator because its deep, concave profile allows larger amounts of wave energy to strike the shoreline. This in turn further aggravates shoreline erosion. This partially explains why the beaches in Carlsbad have been so slow to recover from the last several decades of severe Winter storms. Reference Figure 10. BEFORE PROTECTIVE BEACH LIMIT OF EROSION PRESENT UMIT OF EROSION FIGURE 10 An overview of beach widths along the shoreline between Dana Point and Point La Jolla, referred to as the Oceanside Littoral Cell, reveals the beach widths in the City of Carlsbad to be the narrowest in the entire region. The beach in the City of Carlsbad, looking almost like a small, indented bay, stands in stark contrast to the distinctly wider beaches in the surrounding areas. There appears to be equivalent sediment starvation up and down coast. Reference Figure 11. 10 BEACH WIDTH (FEET) 800 600 400 I 200 I — DOHENEV 8EACH — SAN ONOFRE I OCEANS1DE HARBOR BUENA VISTA LAGOON BATIQUITOS LAGOON •*• DEL MAR LA JOLLA DATA: CORPS OP ENGINEERS, 1986-87 HISTORICAL PERSPECTIVE FIGURE 11 In 1951, Carlsbad was a sleepy coastal town of less than -5,000 permanent residents. Carlsbad was known as a year round vacation destination due primarily to the wide expansive public beaches. Reference Figure 12. Wide, sandy beaches provided protection to the bluff-top private homes, the coast highway, and other public facilities. In 1942, the United States Army Corps of Engineers constructed the Del Mar Boat Basin on the United States Marine Corps Base at Camp Pendleton north of Oceanside to support the important military presence in Northern San Diego County. As a staging and training area, the jetty structures that were constructed by the Corps provided safe access to the basin. In the early 1950's, the Corps widened the mouth of the basin and reconfigured the entrance channel to provide safe access for military craft during all tidal conditions. Reference Figure 13, Today, the United States Marine Corps Base at Camp Pendleton is the largest military amphibious training facility in the world. CARLSBAD, 1951 3 . .-« FIGURE 12 OCEANSIDE, 19 11 In the early 1960's, a public recreational harbor was constructed within the City of Oceanside funded by the United States Army Corps of Engineers south of Camp Pendleton's Del Mar Boat Basin utilizing an extended jetty system. Today, the Oceanside Harbor serves all of Northern San Diego County, including the City of Carlsbad, by providing excellent recreational harbor facilities and commercial fishing enterprises. Reference Figure 14. In viewing Figure 14, it is important to note the shared entrance channel, the width of the beaches in and around the harbor, and the extended harbor entrance jetties. The City of Carlsbad has always been, and continues to be, one of the strongest supporters of the Oceanside Harbor for its military, recreational, commercial, national defense and other interests. EXISTING SEDIMENT STREAM IN THE OCEANSIDE LITTORAL CELL The longshore sediment stream, which continuously nourishes the beach while moving in a surf zone, is deflected seaward at Oceanside. This occurs to the sediment stream arriving at this location from both the north and south. Recent data indicates the deflected sediment reaches water depths of as much as 40 to 60 feet which is too far off-shore to ever return to the surf zone. There is some further indication that this sediment on the off-shore bed continues its journey southward under the influence of the wind induced coastal jets, however, remaining in approximately the same depths of 40 to 60 feet. If true, this path completely by-passes the coastline south of Oceanside, directly impacting the Carlsbad beaches. Reference Figure 15. Today, the shoreline between the Buena Vista Lagoon on the north and Batiquitos Lagoon on the south within the City of Carlsbad, is essentially a cobble beach with very little measurable sand. EXISTING SEDIMENT STREAM IN OCEANSIDE LITTORAL CELL OANA POINT LEGENO SEDIMENT PATH DEPOSITION EANSIDE HARBOR FIGURE 15 »»'••» - —&c« .V. 12 There is some concern that the harbor presence, because of its location and jetty configuration, interrupts the sediment path causing a deflection of material into deeper water. Sand tends to travel and is therefore deposited with regularity in approximately 25 feet of water. Most coastal engineers agree that suspended sediment in depths greater than 25 feet are lost from the littoral drift. It is estimated that approximately 440,000 cubic yards of sand are deflected into deeper water and lost from the littoral drift each year. The United States Army Corps of Engineers studies of beach profiles taken in 1934 prior to the configuration of the Del Mar Boat Basin and the Oceanside Harbor, and again in 1972 after these events, indicate an emerging accretion of sand at approximately 40 to 60 feet of water off the Carlsbad coastline. Reference Figure 16. Although not conclusive, there is the strong suspicion that only 25% of the total sand resources within the entire littoral cell are currently available both up and down coast. HISTORICAL SEDIMENT DEFLECTION AT OCEANSIDE HARBOR ANNUALLY ABOUT 440,000 CY OCEANSIDE HARBOR ACCRETION GREATER THAN 2 FT BETWEEN 1934-72 SUSPECTED SEDIMENT PATH FIGURE 16 13 Because of the proximity of the Oceanside Harbor to the Carlsbad beaches, there is the increasing belief of direct, adverse impacts downcoast. Reference Figure 17. OILMAfl 1O*T IAIIN CtTV Of OCI*HM)I OCEANSIDE HARBOR * DELMAR BOAT BASIN ARE APPROXIMATELY 3 MILES FROM THE CITY LIMITS OF CARLSBAD FIGURE 17 SATELLITE IMAGERY Figure 18 is a reproduction of an infra-red thermal graph provided by the National Qceanographic Administration's NIMBUS Satellite taken in 1982. For orientation, the blue area is the coastline within the Oceanside Littoral Cell, from Dana Point in the north to Point La Jolla on the south. The orange and yellow areas depict varying water temperatures. Of importance is the yellow stream in the middle of the graph extending off-coast in a southwesterly direction and in a circular configuration. This indicates wave currents of warmer waters traditionally closer to shore which had been deflected seaward. The point along the coastline which is believed to be the origin of the deflection is approximately the area of the Oceanside Harbor. 14 SUSPECTED INFLUENCE OF OCEANSIDE HARBOR A search of the available literature reveals more than a passing consideration of the suspected influences of the Oceanside Harbor and its extended j etty structures upon downcoast beaches, particularly those in Carlsbad. William Herron, former Chief of the Coastal Engineering Branch and Head of the Beach Erosion Control Section of the United States Army Corps of Engineers, Los Angeles District Office, from 1954 - 1970, stated in a 1986 Corps of Engineers Report entitled, "Oral History of Coastal Engineering Activities in Southern California, 1930 to 1981": "This beach erosion problem has actually been gradually extending downcoast until it now affects the entire shorefront of Oceanside and Carlsbad, the adjacent City to the south, and it is beginning to extend on down below the Agua Hedionda Lagoon." Mr. Herron, who presided over the coast of Southern California for over twenty (20) years as the leading Corps of Engineers expert on local coastal processes, made the following statement in a 1983 article published in Shore and Beach magazine: "This combination of the Harbor interference with littoral sand movement and the long term lack of natural supply of beach sand from the rivers has caused extensive erosion of the Oceanside beach and the City of Carlsbad, a distance of about ten (10) miles." Dr. Douglas L. Inman, noted scientist on coastal processes at the Scripps Institution of Oceanography, has also raised the belief that erosion damage caused by the Oceanside Harbor extends into the City of Carlsbad. In a 1983 consultant report prepared for the City of Oceanside, entitled, "Oceanographic Report for Oceanside Beach Facilities," Dr. Inman states: "During the forty (40) year period from 1942 to 1982, an erosion of 6.0 million cubic yards occurred mostly in the 6,000 yard length of coast from about 6th Street to Buena Vista Lagoon... The erosion extends south of Oceanside, but there are not adequate surveys to estimate the rates." "The most striking feature is the erosion of about 2.5 million cubic meters (3.3 million cubic yards) from the 5.5 km (18,000 ft) length of beach downcoast from the harbor. Further, the erosion appears to extend well beyond the southern survey limit at COE range S-24 (a point 2,000 ft south of Buena Vista Lagoon - editor)." 15 Gerald Kuhn, Senior Scientist at Scripps Institution of Oceanography, a well known author of a number of publications and reports on bluff erosion in San Diego County and Dr. Francis P. Shepard, Professor Emeritus at Scripps Institution of Oceanography, widely recognized as the leader of modern marine geology and for numerous research works on coastal sediment in Southern California stated in a 1985 Duke University Press publication entitled, "Living with the California Coast," stated the following: "The jetties at the harbor mouths have cut off the sand moving southward, which nourished the wide beaches in the Carlsbad and Oceanside areas." CONCLUSION The City of Carlsbad's concerns about the current beach erosion situation and potential damage and costs to both public and private facilities from future storms is well founded. To date, there is not a definitive investigation of the causes, sources, and potential solutions to an existing and on-going problem. The City believes there is a clear and present federal interest and responsibility to investigate and mitigate downcoast effects from the Corps' Oceanside Harbor Proi ect with the obi ective of minimizing continuing erosion and future damage. This can best be accomplished by a Corps sponsored Carlsbad Beach Erosion Study to begin at the earliest opportunity. 16 ACKNOWLEDGEMENTS The City of Carlsbad wishes to acknowledge and express its appreciation for the assistance, cooperation, and technical work of the following: Louis J. Lee, P.E. Woodward-Clyde Consultants, Incorporated San Diego, California Dr. Choule Sonu, President Tekmarine, Incorporated Pasadena, California Municipal Projects Staff City of Carlsbad Carlsbad, California