CHAPTER 5C: SHORELINE EROSION
The physical configuration of the California shoreline is dynamic and constantly changing due to coastal erosion. The rate of this erosion is determined by natural events, such as rough seas, high tides, nearshore currents, rainfall and runoff, landslides, and earthquakes, as well as human developments that restrict the sources of sand for beaches. Historically, most beaches in California were relatively narrow, but varied depending on the factors influencing erosion. In the last 20 years, the State has suffered major public and private property losses from severe erosion in such coastal areas as Marin, Santa Cruz, San Luis Obispo, Santa Barbara, Los Angeles, Orange and San Diego counties. The challenges for the State of California are to better understand its eroding coastline and to improve its assessment of how natural and economic resources can be protected.
BACKGROUND
California's beaches, coastal bluffs, bays, estuaries, and other shoreline features are altered according to the availability of beach sand, the wave and current energy impinging on the coast, and other physical processes that affect the movement of sand. A constant supply of sand is necessary for beaches to form and be maintained along this shoreline. Many human activities have unfortunately reduced the supply of sand that reaches the ocean and, in turn, deprive beaches of replenishment. These activities include dam construction, river channelization, and other developments. Lack of replenishment creates greater vulnerability for shorelines that have always been subject to varying levels of erosion. There are few practical solutions to improving sand supply from inland sources, so management of shoreline erosion will likely continue to focus at the land/sea interface along the California coastline.
Sand is transported along the coast (long shore transport) by wave-induced nearshore currents, providing vital sand flow for California beaches. Construction of breakwaters, jetties, or groin fields to protect harbor entrances, maintain beaches, or protect coastal structures have had both positive and negative impacts on the movement of sand along the shoreline. Protective structures trap sand and allow beaches to expand up coast from the device, but can interrupt the flow of sand to beaches located down coast. The structures protecting Santa Barbara and Oceanside harbors are the two best examples of protective structures in California that provide benefits to the community, but also increase down coast erosion. However, in many cases no adverse down coast impacts occur and the major impact is to increase the width of narrow beaches, providing recreational opportunities and property protection.
Other forces, such as intense storms, can cause serious shoreline retreat (storms in 1982, 1983, and 1995 caused major damage statewide). Such events occasionally force coastal residents to dump boulders (rip-rap) in front of their homes during emergency attempts to save their property. Such emergency measures are costly and reduce shoreline access, although they can be effective if properly engineered and permitted by agencies of jurisdiction.
California's Ocean Resources: An Agenda for the Future Chapter 5C: Shoreline Erosion
The Resources Agency of California July 1995 (Draft)
5C - 1
Coastal Erosion Policy Development
The natural phenomenon of coastal erosion is one of the more difficult statewide planning issues for California to manage. Over 950 miles of the State's 1,100 mile shoreline is actively eroding (Griggs, 1991) and California's population growth, combined with the public's desire to live and play along the ocean, continues to place tremendous pressures on this dynamic region for shoreline development.
The need to develop policies to reduce and manage coastal erosion was identified by the State Department of Navigation and Ocean Development in the 1972 California Comprehensive Ocean Area Plan. In 1975, the Coastal Zone Conservation Commission (predecessor of the California Coastal Commission) issued a Coastal Plan which recognized the need for some shoreline protective devices, but also found that seawalls, breakwaters, and groins impact scenic resources, interrupt sand supply (often increasing erosion down coast), and interfere with public access. When the California Coastal Act was passed in 1976, coastal erosion and beach maintenance policies were included to address these concerns. In 1978, a memorandum was issued by the California Resources Agency to its departments, boards and commissions to provide policy guidance regarding shoreline erosion issues. Although the policy direction in this memorandum is still being used during some State agency reviews of shoreline projects, the document has never been re-evaluated or updated. Determining the best methods for reducing shoreline erosion and protecting coastal structures is frequently done by State and local agencies on a case-by-case basis, which can hinder regional approaches to managing shoreline erosion.
Jurisdictional Overview
In California, the primary government agencies involved with shoreline erosions issues are the U.S. Army Corps of Engineers (Corps) and the Federal Emergency Management Agency (FEMA) at the federal level, and the California Department of Boating and Waterways (DBW), California Coastal Commission, San Francisco Bay Conservation and Development Commission (BCDC), State Lands Commission, State Coastal Conservancy, Department of Conservation's Division of Mines and Geology (DMG), and Department of Parks and Recreation (DPR) at the State level. The Corps, DBW, and sometimes the State Coastal Conservancy are involved with funding shoreline maintenance projects, while the DPR, as a land manager, has to decide whether to re-build and/or protect its facilities after major storms. FEMA has a variety of programs to provide assistance during major incidents of flooding and storm damage, and to assist with efforts to re-build damaged facilities. The California Coastal Commission, State Lands Commission, and BCDC (within San Francisco Bay) are the primary State agencies with regulatory authority over proposals to build coastal protective structures, while the DMG is the lead in identifying geologic hazards for the State. Local governments also process a number of permit actions that involve shoreline protection devices.
ISSUE ANALYSIS
It is unlikely that many projects to construct additional large scale jetties or breakwaters will be proposed in the near future. However, coastal managers will certainly continue to receive applications for projects to construct smaller scale shoreline protective devices for existing structures.
California's Ocean Resources: An Agenda for the Future Chapter 5C: Shoreline Erosion
The Resources Agency of California July 1995 (Draft)
5C - 2
Constructing a Protection Device
Constructing a "hard" protection device, such as a revetment, bulkhead, seawall, or breakwater, is historically the most common approach to reducing shoreline erosion and protecting private or public structures. These structures reduce wave attack and backshore erosion and are often used to protect infrastructure serving the public. For example, the 6000-foot seawall in Carlsbad protects a utility corridor and the only north-south thoroughfare along this portion of coast other than Interstate 5. The 54-year old O'Shaughnessy seawall at Ocean Beach in San Francisco, which protects Highway 1, is a similar example. These structures provide greater public safety by protecting infrastructure and improving public access.
Although protective structures can have positive benefits, the potential adverse impacts of these structures must also be considered, which can include limiting public access to the shoreline, increasing erosion down coast, restricting sand input from protected bluffs, and increasing visual disruption along the shore. Additionally, these structures are sometimes constructed on an emergency basis during heavy storm activity without proper engineering or appropriate materials. This can lead to eventual failure of the device and subsequent public hazards along the beach.
While protective structures may be constructed to protect existing development or coastal-dependent facilities, the California Coastal Act requires that new, non-coastal dependent developments not be built if it is known that the development will require a protective structure in the future.
Beach Nourishment or Replenishment
Beaches can be nourished by depositing sand up coast or directly on a beach to increase its width. The primary difficulties of this approach are cost and responsibility for the operation; source and method of sand extraction for nourishment use; direct smothering of marine life or important habitats; and transporting large quantities of sand to the site. Benefits include the economic and aesthetic values of a wide recreational beach and the decreased need for backshore protection. For example, the State and federal governments have provided funding for beach nourishment projects at Surfside-Sunset beach in Orange County, providing major economic and recreational benefits to that community.
Relocating Ocean Front Structures
Relocating a structure farther inland can be less expensive than rebuilding the structure if it is destroyed. However, there is little incentive for this option to be seriously considered. Under the California Coastal Act, a coastal development permit is not required for the re-construction of any property destroyed by a natural disaster if the replacement structure footprint remains substantially the same (no more than 10% change from the original structure). Therefore, redevelopment after a natural disaster can include the same design or location that contributed to the first episode of property loss.
California's Ocean Resources: An Agenda for the Future Chapter 5C: Shoreline Erosion
The Resources Agency of California July 1995 (Draft)
5C - 3
Coastal Hazard Avoidance
Avoiding new development may be considered in areas where a new structure would require extensive engineering solutions to prevent further coastal erosion and which could still pose hazards on the property or to adjacent properties. In such cases, avoidance would reduce costs associated with future disaster relief, construction of protective devices, and government disaster assistance.
FINDINGS AND RECOMMENDATIONS
Finding
The vast majority of the California coastline is actively eroding, which has been accelerated by natural events and human alterations to the environment. A variety of project-specific and regional approaches are available for addressing the issue of coastal erosion. Although some regional inventory approaches have been developed for coastal communities, no up-to-date statewide coastal hazards inventory is currently available. Additionally, the expertise to address these problems is distributed between several agencies in State government.
California's Ocean Resources: An Agenda for the Future Chapter 5C: Shoreline Erosion
The Resources Agency of California July 1995 (Draft)
5C - 4