Consultants recommend multipurpose offshore breakwaters, prefill sand to retain beach sand in San Clemente

Consultants with Moffatt & Nichol presented a draft Nature‑Based Feasibility Study to the Coastal Advisory Committee on May 15, outlining offshore breakwater/reef concepts intended to trap sand and lengthen the interval between nourishment cycles. The firm proposed pilot projects at North Beach, Capistrano Shores and the south end of the city, and gave preliminary estimates of filled areas, sand volumes and costs for each concept.

Why it matters: The study seeks to move San Clemente from repeated short‑term sand placements toward infrastructure that retains sand longer, potentially reducing long‑term replenishment frequency and protecting shoreline infrastructure, recreation and habitat.

Key consultant findings and concepts - North Beach “dog‑bone” breakwater: a multipurpose emergent structure the consultants sketched as roughly one quarter mile long with a roughly 700‑foot planform width. Moffatt & Nichol reported that a prefill of 400,000–600,000 cubic yards (they cited 500,000 cy as an illustrative midpoint) would likely be required to create an 8–13 acre beach in the structure’s lee. The consultants said such a feature would block incoming wave energy, produce a quiet swimming area behind the breakwater and could be shaped to provide surfable edges. - Capistrano Shores submerged breakwater: a longer but lower structure sited in deeper water and intended to be mostly underwater (the crest near mean lower low water). The consultants estimated it could create roughly 20 acres of new beach but would require a much larger prefill — they cited about 1.5 million cubic yards of sand for the concept as presented. - South‑end breakwater: a design similar to North Beach but slightly smaller in net accreted area (consultants estimated roughly 12 acres). They also noted the potential to use a structure there to stabilize an active toe‑of‑slope landslide in that vicinity and to reduce future repairs to the rail corridor.

Costs, benefits and permitting Moffatt & Nichol provided high‑level cost estimates that put multipurpose reef projects in the tens of millions; depending on footprint and sand sourcing the consultants described program costs on the order of hundreds of millions when accounting for engineering, environmental review, construction, sand procurement and contingencies. The presentation included a benefits‑to‑cost review prepared by a coastal economist; over a 25‑year window the consultant team’s recreational benefits estimate produced a higher benefit for the North Beach concept (presented as roughly $200 million in recreation benefit over 25 years) and lower values for the south end. The consultants noted their economic tally omitted some protective and non‑recreation benefits (for example, avoided emergency armoring), which could improve benefit‑cost ratios if included.

Moffatt & Nichol stressed that the concept drawings rely on regional correlations and that the next steps — numerical coastal modeling and physical laboratory modeling — would be required to refine dimensions, test surf performance and set final volumes. They also listed permits likely needed for any site: U.S. Army Corps of Engineers (River and Harbors Act Section 10 and Clean Water Act Section 404), California Coastal Commission coastal development permits, State Lands Commission, Regional Water Quality Control Board 401 certifications, and right‑of‑entry agreements with OCTA and the regional rail authority if work or staging interacts with rail right‑of‑way.

Timeline and next steps The consultants said they will publish the draft report for a roughly 50‑day public review period (anticipated the week after the committee meeting). If the city advances a pilot, consultants recommended targeted numerical and flume (physical) modeling, followed by environmental review, permitting and staged construction; the consultants estimated a realistic five‑year timeline to pilot implementation if funding and permitting align, with longer time horizons for expanded regional deployment. They identified pilot site optimization — especially moving some footprints slightly closer to shore to reduce cost while preserving benefit — as a near‑term design priority.

Committee reaction and staff follow up Committee members and staff discussed project economics, relative public access and visual impacts, and the potential to align OCTA sand placement or regional programs with a retaining structure to reduce overall costs. The consultants and city staff agreed to incorporate public comments into the draft and to provide the report for grant and funding applications.