US ARMY CORS OF ENGINEERS
Encinitas ““ Solana Beach, San Diego County, CA, Coastal Storm Damage Reduction Project, 21 April 2015
Encinitas ““ Solana BeachABSTRACT: The purpose of the Project is to effectively reduce risks to public safety and economic damages associated with bluff and beach erosion along the shorelines of the cities of Encinitas and Solana Beach. A secondary purpose is to reduce erosion and shoreline narrowing to improve recreational opportunities. The shoreline has narrow beaches with coastal bluffs exposed to crashing waves, particularly during the winter storm season. As sea levels rise, the bluffs will be more frequently exposed to crashing waves, which carve notches into the bluffs. Bluffs affected by these notches are then prone to episodic collapse. Consequently, public facilities and residential properties on the upper bluff experience land loss and damages to the property. In addition to this problem, the study area’s high demand for recreation and narrow beach area combined with bluff failures represent a significant safety issue for those recreating.
The recommended plan for coastal storm damage reduction in Encinitas includes construction of a 50-foot-wide protective berm along a 7,800-foot-long stretch of shoreline using 340,000 cubic yards of compatible sediment, with renourishment, on average, every 5 years over a 50-year period of Federal participation, for a total of nine additional nourishments. The recommended plan for coastal storm damage reduction in Solana Beach includes construction of a 150-foot-wide protective berm along a 7,200-foot-long stretch of shoreline using 700,000 cubic yards of compatible sediment, with renourishment, on average, every 10 years over a 50-year period of Federal participation, for a total of four additional nourishments. The design berm will be constructed to an elevation of +15 feet mean lower low water with a foreshore slope of 10:1. Material for the beach fill will be dredged from borrow sites identified off the coast of San Diego County. Physical monitoring of the performance of the project will be required annually throughout the 50-year period of Federal participation. This plan would provide coastal storm damage reduction throughout the project reach and would maintain the existing recreational beach.
Monitoring of the environmental resources will be required for each construction event. Impacts associated with the project in Encinitas are determined to be less than significant for all resources except for the potential for discovery of unknown cultural resources at the borrow sites during dredging. Impacts associated with the project in Solana Beach are determined to be less than significant for all resources except biological resources, and the potential for discovery of cultural resources at the borrow sites during dredging. Sand introduced into the system along Solana Beach is predicted to indirectly impact up to 6.8 acres of marine biological resources (benthic habitat) as a result of burial or degradation of sensitive habitats and resources. If impacts are identified, functionally equivalent mitigation will be required. Mitigation would reduce impacts to below a level of significance. A comprehensive monitoring and mitigation plan has been incorporated in the project in the event that impacts to habitat result. The recommended plan is a Locally Preferred Plan.
Based on October 2014 price levels, the estimated initial construction cost of the plan is $30,544,000, for which the Federal share is approximately $19,853,600 (65 percent) and the non-Federal share is approximately $10,690,400 (35 percent). Total periodic nourishment costs are estimated to be $134,348,000 (October 2014 price level) over the 50-year period following initiation of construction, for which the Federal share is approximately $67,174,000 (50 percent) and the non-Federal share is approximately $67,174,000 (50 percent). Operation, maintenance, repair, replacement, and rehabilitation costs over the lifetime of the project are estimated to be minimal and within the scope of existing activities performed by both cities (estimate cost of $0).
Based on the current 3.375 percent discount rate and a 50-year period of analysis, the total equivalent average annual costs of the project are estimated to be $3,763,000. The equivalent average annual benefits, which include recreation benefits, are estimated to be $5,360,000 with net average annual benefits of $1,597,000. Including all estimated recreational benefits, the benefit-cost ratio is approximately 1.4 to 1.
Report Documentation: Pertinent documentation on the project, the results of the Civil Works Review Board and subsequent Washington-Level Review Actions are listed below (items not linked will be provided when available):
“¢CWRB Briefing Slides
“¢CWRB Lessons Learned
“¢CWRB Meeting Record
“¢State & Agency Review Comments Letters
“¢Documentation of Review Findings
“¢Signed Chief of Engineers Report
“¢Advanced Copy to Congressional Committees
“¢ASA (CW) Memo to OMB
“¢ASA (CW) Transmittal to Congress
“¢Signed Record of Decision
Additional Information: South Pacific Division Los Angeles District