Proposed San Clemente Sand Source Offshore Investigation The City seeks to identify potential offshore borrow sites and verify suitability of material to support beach restoration efforts in San Clemente and potentially greater South Orange County. Particular emphasis will be placed on delineating the material with the best grain size characteristics for beach nourishment.
A geophysical investigation will be conducted in a four-phase approach which will take up to 18 months to complete. Receiver site characteristics will be defined as part of the first phase. The second phase consists of evaluation of existing information (literature review) to identify potential borrow sites and to guide subsequent field data collection efforts. Once the candidate sites are identified, marine geophysical (seismic reflection profiling) surveys will be performed. The results of the marine geophysical surveys will be interpreted and used to develop a focused vibracore sediment sampling and analysis program. Depending on the nature of available historical information, geophysical surveys may not be warranted at all candidate borrow sites.
Phase 1. Receiver Site Characterization
Define Receiver Site Characteristics: Obtain and analyze surficial sediment samples at up to three candidate receiver sites to determine sand characteristics (grain size distribution). Samples will be obtained from the back beach to a depth of 30 ft, Mean Lower Low Water. This information will be used to evaluate compatibility of potential source material.
Phase 2. Evaluation of Existing Information and Plan Formulation:
Evaluate Existing Information: Collect and review existing data for potential offshore sand borrow sites from various sources including federal and state agencies, universities, local cities and counties to evaluate potential candidate sand sources for beach nourishment (e.g., Fischer, et al, 1983; Osborne, et al, 1983; Orange County, 2013, URS, 2009; US Army Corps of Engineers, 2012.) Identify Candidate Borrow Sites: Select up to three potential borrow sites to investigate. The sites will be selected based on proximity to proposed receiver sites, potential to provide required sand volume, potential to yield suitable material, and likelihood of being able to utilize the borrow site (e.g., environmental issues, permitting issues, jurisdictional conflicts). The number of sites investigated may be adjusted based on available budget.
Prepare Field Investigation Plan: Develop plan for geophysical investigation of the potential borrow sites, including acquisition of necessary permits.
Phase 3. Marine Geophysical Surveys:
Conduct Geophysical Survey Program: The need to conduct geophysical surveys will be evaluated based on the nature of historical information for each candidate site. Conduct marine geophysical surveys at the candidate sand source sites as warranted. The surveys will be designed to focus on the upper 30 ft of sediment, as dredging operations will likely be limited beyond this depth.
Preliminary Interpretation: The results of the marine geophysical surveys will be interpreted and used to focus the sediment sampling effort undertaken during the next phase (Phase 4) of the investigation.
Final Evaluation of Results: Upon completion of the vibracore sediment sampling activities (Phase 4), additional interpretation of the geophysical data shall be conducted using this “ground-truth” information.
Phase 4. Sediment Sampling
Prepare Sampling and Analysis Plan (SAP): Prepare a SAP designed to evaluate compatibly of potential source material. The plan will include sample locations, physical (grain size) and chemical testing protocols, and quality assurance/quality control procedures. The results of the receiver site characterization conducted in Phase 1 will be included in the plan. A draft plan will be submitted to the U.S. Army Corps of Engineers (USACE), U.S. Environmental Protection Agency (USEPA) standards, and Regional Water Quality Control Board (RWQCB) for concurrence before finalizing.
Conduct Sediment Sampling Program: Conduct a vibracoring program to confirm the interpretation of the marine geophysical surveys (or historical information) and determine the physical (grain size distribution) and chemical characteristics of the sediment at each candidate borrow site. The coring apparatus will be capable of achieving 20 ft penetration in suitable sediments.
Evaluate Borrow Site Sediment Characteristics: The cores will be handled, tested, and evaluated in accordance with the Sampling and Analysis Plan.
References
Fischer, P.J., Kreutzer, P.A., Morrison, L.R., Rudat, J.A., Ticken, E.J., Webb, J.F., Woods, M.M., Berry, R.W., Henry, M.J., Hoyt, D.H., and Young, M., 1983, “Study on Quaternary shelf deposits (sand and gravel) of Southern California”, Submitted to State of California, Department of Boating and Waterways, Beach Erosion Control Project, FR 82-11, 66 p.
Orange County, 2013. Coastal Regional Sediment Management Plan. Prepared for the U.S. Army Corps of Engineers and California Coastal Sediment Management Workgroup. 212 pp.
Osbourne, R.H., N.J. Darigo, and R.C. Scheidemann, 1983, “Report of Potential Offshore Sand and Gravel Resources of the Inner Continental Shelf of Southern California”, prepared for Calif. State Dept. of Boating and Waterways, Sacramento. University of Southern California, Dept. of Geological Services, Los Angeles, CA, 302 pp.
U.S. Army Corps of Engineers, 2012, San Clemente Shoreline Feasibility Study – Geotechnical Appendix” U.S. Army Corps of Engineers, Los Angeles District.
URS, 2009, “Geotechnical Assessment-Offshore Sand Sources-Regional Beach Sand Project II-San Diego, CA”. report prepared for SANDA and Moffatt & Nichol, San Diego, CA, 20pp+app.
Preliminary Cost Estimate
Phase 1. Receiver Site Characterization $35,000
Phase 2. Evaluation of Existing Information and Plan Formulation $70,000 Phase 3. Marine Geophysical Surveys $265,000
Phase 4. Sediment Sampling $390,000
Total Cost $760,000
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