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Coastal Development Coastal Armoring
About 85% of the California coast experiences active erosion due to natural, and anthropogenic causes. Storm damage continually erodes away at the coastline, most notably during El Nino years such as the 1982-83 episode, and other heavy storms 1. The construction of hard surfaces such as concrete, covering large portions of land, impedes the natural absorption of water, thus exacerbating the problem of erosion. Furthermore, in some areas natural sand transport to our coasts has been decreased through the damming of streams and rivers. Increases in coastal development have also led to storm related damage. More...
In response to these issues, structures have been used extensively along California’s coastline to protect the coast from wave action, or to retain soil to avoid erosion. This armoring has typically occurred because property values are at stake and property owners consider it a threat to the value of their real estate. This phenomenon is commonly known as coastal armoring, and includes seawalls, bulkheads and revetments. Vertical structures are either seawalls or bulkheads depending on their purpose. A bulkhead is used as a retainer, providing protection and stabilizing the land that it supports. Conversely, a seawall is normally a bulkier structure designed for the purpose of wave interception. Revetments are protective structures placed along slopes and are constructed of a sturdy material such as stone. With increases in development, additional pressures will come to install structures both to access the coast and to protect property from the ocean.
The Army Corps Of Engineers conducted an assessment of coastal armoring in 1971, and found that 3 miles of a study area spanning the coastline between the Santa Cruz/San Mateo county border, and Point Lobos in Monterey County was armored (all in the City of Santa Cruz). By 1978 armoring had increased to 9.6 miles, and in 1993, 12 miles was protected by structures. The California Coastal Commission estimated in 1995, that if trends continue at current rates, there would be as much as 27.7 miles of coastal armoring in the same area, in the future. The commission stated that although only one-eighth of the study area was armored in 1995, onethird of the coastline has the potential to warrant future protection when considering land use patterns, and physical characteristics. In California, around twelve percent of the coastline (130 miles) was armored in 1998. Between 1985 and 1990, forty-five miles of this armoring was erected, costing an average of $1,500 per foot ($60 million/year). Currently, California residents pay over $75 million per year to armor the shoreline. In a study conducted by Griggs et. al., in 1992, it was determined that ocean front development has continually occurred in California, in the face of a large amount of scientific evidence regarding the risks of erosion. The authors also concluded that existing state and local policy had a large degree of inconsistency in the way that they deal with coastal hazards, and that there was a significant economic and political influence.
impacts of Coastal Armoring:
With appropriate mitigation, environmental impacts that occur during the construction phase of coastal armoring projects are generally short term, lasting only a few days to a few weeks. Problems include increased turbidity caused by suspended solids in the immediate vicinity of the construction site, and the risk of chemicals or other materials entering the ocean from construction activities. Structures constructed in the intertidal zone have more impact than those constructed in other locations. Certain types of coastal armoring structures, such as riprap revetments have fewer initial impacts than other hard structures, since construction normally requires significantly less excavation. Permanent impacts of revetments however, are similar to those of seawalls, and the footprint of the revetment is typically larger. Mitigation measures include scheduling of the construction phase to reduce impacts by considering animal migration patterns, spawning patterns, etc, and specific actions such as the use of a silt curtain.
As with any activity that alters natural processes, there can be significant long-term impacts related to coastal armoring. Armoring of the coast tends to interfere with littoral transport, which reaches a dynamic equilibrium in a natural state. The currents, waves, and wind normally transport sediment, which is supplied at a particular site. When the availability of sediment is cut off due to the existence of a structure, erosion tends to occur in other locations. This is due to starvation of the materials that would normally supply these areas. When a structure is constructed, the supply of sediment is effectively being cut off. Armoring also causes deflection of wave energy, which can lead to accelerated erosion of nearby sites, which may subsequently require armoring structures. Vertical structures in particular can deflect wave energy causing increased erosion and altering natural habitat in front of the structure, and may make it difficult for organisms to inhabit the area because of high turbidity etc. Erosion caused by the reflection of wave energy is more severe with vertical structures than with curved stepped or inclined structures, which absorb or disperse the energy of the waves Depending on materials used, coastal armoring structures can influence the structure of benthic communities, due to potential differences in settlement patterns for natural substrates and armoring structures. Other impacts include encroachment of structures into the intertidal, or disturbance of important buffer areas such as marsh habitat between the marine and terrestrial environments, which naturally mitigate erosion, and alteration of the flushing rates of certain contaminants.
MBNMS Currently Addressing Coastal Armoring?
MBNMS has reviewed and authorized Coastal Commission permits for seawalls, riprap or other coastal armoring projects at 16 sites since its designation. Only a portion of the total number of coastal armoring projects underway in the region came to the Sanctuary for review. Of these permits, six were issued for extension and/or repair of existing seawalls, four for seawall or revetment construction, two for road stabilization projects to prevent bluff erosion, two for replacement of rip-rap with seawall, and one for stabilizing and making additions to existing riprap. Eleven of these 16 permits were in Santa Cruz County, 3 were in San Luis Obispo County, and 1 was in Pebble Beach in Monterey County.
Development along the coast increases the pressure to protect coastal structures with various types of coastal armoring such as seawalls, bulkheads and revetments to manage erosion. Approximately 14 miles of the coastline is already armored in the MBNMS, and this is estimated to double if trends continue at current rates. In light of this situation, MBNMS staff recently initiated a joint evaluation of coastal armoring with the California Coastal Commission, to develop a more proactive, comprehensive regional approach, improve the current case by case permit system and strengthen coordination between the Coastal Commission and the MBNMS on coastal armoring permit review.
Objective I: Improve the current case-by-case permit system and strengthen coordination between the MBNMS and other agencies on coastal armoring permits - Action Items:
• Identify permit conditions and authorization criteria of the agencies involved in the regulation of costal armoring.
• Compare typical multi-agency seawall permit conditions, identify and discuss selected discrepancies, and where possible rectify discrepencies• Incorporate MBNMS typical conditions into CCC permits, where possible
• Develop system for MBNMS handling and level of involvement in small versus large projects, given severe staff constraints• Develop criteria for full MBNMS review of selected projects based on scale, location, etc.
• Define threshold below which MBNMS does not individually review project, but relies on CCC permit review process to incorporate standard MBNMS conditions
• Improve sharing of project and permitinformation at early stages, for those projects that meet the threshold permit criteria for full MBNMS review
Objective II: Characterize the issue and determine information needs. Identify existing information and data gaps, and compile and produce scientific data and evaluation tools - Action Items:
• Develop Sanctuary-wide map of existing coastal armoring sites and potential future site requests
• Assess coastal bluff erosion rates (CCC with NOAA Coastal Fellow)
• Compile or conduct regional evaluation of sand transport dynamics and beach nourishment
• Assess individual and cumulative impacts of coastal armoring on sand supply dynamics, marine biological habitats and ecosystems, and public access
• Develop regional integrated database and GIS layers showing land use parcels, coastal armoring locations, bluff erosion rates, bottom types, biological habitats etc. for use as a planning tool and for permit review
Objective III: Develop a more proactive and comprehensive regional approach to coastal armoring - Action Items:
• Develop guidelines for a sub-regional planning approach to coastal armoring—e.g. pristine or particularly sensitive areas where coastal armoring should be strongly discouraged or not allowed, urban zones which are already heavily armored and where efforts should focus on restoration and improved armoring techniques, and areas inbetween where thorough case-by-case review and additional research is needed
• Identify appropriate planning sub-regions. Logical sub-regions might be only a mile or two in some urban areas such as Santa Cruz, but could range up to many miles for long stretches of rural coastline such as Big Sur. Criteria to consider in establishing boundaries include: extent of existing armoring in area; types of armoring in place; potential for new armoring requests in area; types of structures to be protected; level of development in area (pristine, heavily developed, or somewhere in between); biological sensitivity of habitats; geological units; beach nourishment needs, and; shoreline orientation and erosion rates
• Develop specific guidelines for each sub-region.
• Identify preferred types of coastal armoring, including more natural alternatives for specific conditions and geographic locations, taking into account environmental, aesthetic and public access concerns • Identify preventative measures aimed at reducing the need for coastal armoring. Considerations may include increased setback requirements, incorporation of a “no seawall” policy for situations when coastal agricultural land is converted to development, and requiring new setback requirements to be established for demolition/rebuild projects in urbanized areas
• Reduce the of use emergency permits through better predictive erosion analyses, potential alteration of current guidelines regarding initiation of work, and more proactive regional planning. Consider urban or semi-rural areas where it is appropriate to either initiate the work earlier on or develop alternative solutions, before the site becomes an emergency.
• If warranted based on above scientific evaluation, development of an environmentallysound sand supply program funded by coastal armoring applicants.
Objective IV: Conduct outreach and education efforts - Action Items:
• Conduct regional trainings for local government, developers, etc. to educate about regional approach to addressing coastal armoring
• Clarify Sanctuary’s role in regulation of coastal armoring• Develop framework to strengthen coordination between the agencies on coastal armoring permits.
• Outline a regional policy approach to addressing the issue of shoreline erosion and coastal armoring, and identify different planning sub-regions.• Develop specific strategies for different regions, and integrate into the management plan
California Coastal Commission. ReCAP Pilot Project Findings and Recommendations: Monterey Bay Region. September, 1995.
US Army Corps of Engineers. Engineer Manual. Design of Coastal Revetments Seawalls, and Bulkheads. 1995.
Griggs, Gary. 1998. California Needs a Coastal Hazards Policy. Coast and Ocean Magazine. http://www.coastalconservancy.ca.gov/coast&ocean/autumn98/a04.htm
Downing, John. 1983. The Coast of Puget Sound Its Processes and Development. Seattle. Washington Seagrant Publication, University of Washington Press. Pages 100-113.
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