EVEREST June, 2013 - California Department of Boating and ...

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Orange County Coastal Regional Sediment Management Plan City of Dana Point, neighborhood of Capistrano Beach (within the City of Dana Point), and the City of San Clemente. This region is characterized by varying low and high-relief coastal sections which are somewhat regular in plan, consisting of long smoothly curving sandy beaches backed by roads, railroads, and seacliffs. Primary sediment sources to this portion of the cell are the San Juan, San Clemente and San Mateo Creeks as well as recent beach nourishments. Key quantitative sediment components of this portion of the littoral cell as determined by USACE (1991) include the following: • Under post-dam (after 1938) conditions, sand and gravel contributions in the sediment budget were from 38,000 to 39,000 yd 3 /year from San Juan Creek. The San Clemente Shoreline Feasibility Study (USACE, 2011b) quotes sediment contributions from San Juan Creek as being from 8,000 to 52,071 yd 3 /year and uses an average rate of 27,000 yd 3 /year;. • Under post-dam (after 1938) conditions, sand and gravel contributions in the sediment budget were zero from San Clemente Creek (also known as Prima Deshecha Canada and Segunda Deschecha Canada); and 20,000 yd 3 /year from the combined San Mateo and San Onofre Creeks • No sediment contributions were attributed to coastal bluffs in this reach, but 22,000 yd 3 /year were attributed to coastal terrace erosion from 1933 to 1987. • From 1945 to 1987 about 1,000 yd 3 /year came into the littoral cell from the northern boundary at Dana Point. • From 1945 to 1977 less than 50,000 yd 3 /year of sediment left this portion of the littoral cell across the southern boundary at San Mateo Point. From 1978 to 1987 from 0 to 10,000 yd 3 /year passed this boundary in southerly net transport. • No material was lost offshore in this portion of the cell between 1934 and 1972, none was lost into submarine canyons, and Aeolian loss is negligible. 2.3.5 Sea Level Rise Impacts on Beaches The effect of sea level rise will likely cause increased inundation of the entire coastal zone. Within this zone, coastal RSM impacts from sea level rise would likely be limited to beaches and wetlands. Sea level rise impacts to wetlands will likely result in increased inundation, and changes to habitat distributions. In some cases this can be mitigated through addition of fill material which can fall under the umbrella of coastal RSM. Sea level rise impacts to beaches would likely result in narrowing of those beaches. As sea level rises relative to land (assuming other sediment budget components remain relatively Everest International Consultants, Inc. 2.17
Orange County Coastal Regional Sediment Management Plan constant and wave activity does not change dramatically), current theory holds that the sea floor profile in the surf zone will maintain the same shape as historically existed, moving upward with the rising sea level (Bruun, 1962; USACE, 2011c). The sand needed to maintain this shape is expected to come from existing beaches, thus the entire profile is expected to migrate landward. If the back beach remains fixed, beaches are expected to become narrower to maintain an equilibrium profile and beach narrowing is expected to accelerate if no action is taken to offset these losses. One possible mechanism to counter sea level rise induced shoreline erosion is through beach nourishment. The Bruun Rule (Bruun, 1962) has been used to calculate beach nourishment volumes to offset various sea level rise scenarios for all of southern California (Flick and Ewing, 2009). This type of analysis may be useful for estimating nourishment volumes to offset sea level rise in Orange County. Coastal RSM is one mechanism to counter the effects of sea level rise and maintain functional wetlands and beaches. Since future sea level rise is expected to accelerate with passing time (see Figure 2.4), it is an important factor that needs to be considered for project designs. As the Plan moves forward, coastal projects that are either proposed or modified should include detailed analyses of sea level rise impacts during environmental review, permitting, and engineering design. 2.4 Socioeconomic Aspects This section of the report provides an overview of population trends, beach attendance, beach access, beach amenities, and other recreational opportunities provided within Orange County beaches. These factors are essential in understanding the recreational value of these beaches and if and how much beach maintenance is worthwhile. 2.4.1 Regional Population Trends According to the California Department of Finance (2012), Orange County currently has just over 3 million people, representing about 8 percent of the total population of California. Although the precise relationship between population and the demand for beaches is unknown, it is reasonable to assume that the demand will grow somewhat in line with local population growth. Table 2.3 presents population estimates from the California Department of Finance (2012) for regions important to the Project. Orange County’s population is projected to grow at 0.66 percent per year over the coming decade, but it is projected to slow to 0.16 percent after 2040, largely due to anticipated limits placed on the growth of residential housing. This rate of growth is significantly slower than the projected state average. However, the inland counties of San Bernardino and Riverside, which also provide a significant number of beach visitors, are projected to grow at much higher rates over the next 40 years. If the number of visitors to beaches in Orange County grows at the same rate as population growth for Orange County, then the number of visitors to Orange County Beaches would grow by a total of 18% over 2010 values. Cumulative growth for Everest International Consultants, Inc. 2.18
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EVEREST June, 2013 - California Department of Boating and ...

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