Research Technical Report
A PDF version of this report is available at:
Coastal Regional Sediment Management Plan for Southern Monterey Bay
Philip Williams & Associates, Ltd., E. Thornton, J. Dugan, and Halcrow Group (November 2008)
Prepared for Association of Monterey Bay Area Governments and the Coastal Sediment Management Workgroup, 3 November 2008, PWA REF. 1902.00, 218pp.
Geographic and Historic Setting
Over the next 50 years, the coastal dunes of southern Monterey Bay between the Salinas River mouth and Wharf II in Monterey are predicted to erode at rates between 1.0 and 6.0 ft/year. Over this planning time frame, eight oceanfront facilities are at high risk due to this erosion, and will require mitigation measures to be implemented to prevent their loss. Six of these facilities; Sand City and Tioga Avenue west of Highway 1, Seaside Pump Station, Monterey Interceptor between Seaside Pump Station and Wharf II, Monterey Beach Resort, Ocean Harbor House condominiums, and Monterey La Playa town homes, are located along the shoreline of the Cities of Sand City, Seaside, and Monterey (the southern bight). The other two facilities are the Sanctuary Beach Resort and Marina Coast Water District buildings, located in Marina one mile south of the only remaining beach-sand mining operation on the west coast of the U.S.
Recognizing that the issue of coastal erosion could not be addressed on a city-by-city basis, the City of Monterey sought to form a regional consortium of local, state and federal agencies to determine what can be done to address this issue. Around the same time, as part of a process to update the Sanctuary's Management Plan, the Monterey Bay National Marine Sanctuary (MBNMS) developed an action plan to address the issues of coastal erosion and armoring along the Sanctuary's 276 miles of shoreline. This MBNMS action plan called for the development of a collaborative regional planning approach to address, along with other issues, coastal erosion in the southern Monterey Bay region. This led to the formation of the Southern Monterey Bay Coastal Erosion Workgroup (SMBCEW). The SMBCEW has developed an extensive list of ways to potentially address the issue of coastal erosion, and will be evaluating the applicability of those potential technologies to southern Monterey Bay erosion problems in the near future.
Regional Sediment Management
The California Coastal Sediment Management Workgroup (CSMW) is working with regional stakeholder groups such as the AMBAG and SMBCEW to develop Coastal Regional Sediment Management (RSM) Plans within specific regions of coastal California to help city, county, and coastal managers, and local and state-wide regulatory personnel identify and resolve issues of concern within that region. This Coastal RSM Plan examines a subset of the options to be explored by the SMBCEW, specifically those options that restore coastal habitat by removing or lessening disturbances to natural sedimentary processes that exacerbate coastal erosion. Within this subset, this Coastal RSM Plan recommends implementing the following four regional sediment management strategies for the southern Monterey Bay shoreline:
1. Investigate beach nourishment and other beach restoration strategies to ameliorate erosion in the stretch of shoreline within the Cities of Sand City, Seaside, and Monterey. Here, the majority of high risk facilities are located, and healthy beaches are particularly important for recreation and tourism. Beach nourishment is feasible in the southern bight for a number of reasons. Low wave energy, low sand transport, and the location within a defined sub-cell (the southern bight is nearly self-contained in terms of sand transport) means that any placed sand would remain at the site for a longer period of time. This Coastal RSM Plan shows that there is clear economic justification for beach nourishment of the southern bight and it has the potential to deliver substantial benefits for the recreational value of the shoreline and for protection of its infrastructure assets. Beach nourishment may also reduce the need for 'hard' shore protection, and provide ecologic benefits associated with wider beaches.
2. Reduce or eliminate removal of sand from the beach at Marina. The large extraction of beach sand permanently removes sediment that would otherwise feed beaches elsewhere along southern Monterey Bay. If this sand is released and subsequently transported alongshore, it could provide a significant additional buffer to dune erosion by waves. The effect would be more immediate at the Sanctuary Beach Resort and Marina Coast Water District buildings critical erosion sites, but would eventually benefit the shoreline further away as the sand migrates. The U.S. Army Corps of Engineers has reportedly issued a 'determination of non-jurisdiction' which allows the mining of beach sand at Marina to proceed without a permit from the Corps. The operation started prior to the passage of the California Coastal Act (1972) and therefore may be 'grandfathered' into legal nonconforming use. This Coastal RSM Plan recommends several potential routes that could be taken to reduce or eliminate removal of beach sand at Marina including:
- Communication of the economic impacts of erosion associated with beach-sand mining on down coast communities
- Revisit the U.S. Army Corps of Engineers determination of non-jurisdiction
- Determine whether a change in operations post-1976 (i.e. the increased extraction with introduction of a new dredge sometime after 1979) requires a new permit from the City of Marina.
- Communication of impacts that the beach-sand mining is having on endangered species
- Examine the possibility of alternative mining operations.
3. Allow dune erosion to continue without human intervention north of Sand City to the Salinas River. This erosion will continue to provide large quantities of sand to the beaches, maintaining their healthy condition and provide benefits for sensitive species and habitats, and recreation and tourism. Apart from the Sanctuary Beach Resort and Marina Coast Water District buildings, this area does not contain any facilities at high risk of erosion.
4. Use this Coastal RSM Plan as a baseline to build a regionally comprehensive erosion abatement approach through the ongoing efforts of the Southern Monterey Bay Coastal Erosion Workgroup (SMBCEW). The SMBCEW is preparing to evaluate additional erosion control methods, including retention structures such as offshore reefs, beach dewatering and pressure equalizing modules, and other technologies that could help reduce coastal erosion along the southern Monterey Bay shoreline. The information gathered for the RSM framework presented within this Coastal RSM Plan will provide the basis for evaluating the feasibility of potential erosion control technologies that will work locally and address regional sediment imbalances that are aggravating coastal erosion. Taken together, these two interconnected efforts should collectively provide valuable guidance and reference to city coastal managers, local and state-wide regulatory personnel, the AMBAGs Board of Directors, and state and federal funding entities, thereby setting the stage for specific projects to reduce coastal erosion.