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Why Does North County Have So Much Trouble Retaining Sandy Beaches?

This study conducted by O'Reilly and others from Scripps Institution of Oceanography investigates the reasons behind the difficulty in retaining sandy beaches in North County, Southern California. The research explores wave processes, island sheltering, hot spots, and lagoon sub-cells, highlighting erosion hot spots and the role of incident waves in sand transport. The study also discusses potential solutions such as sand borrow sites and artificial surfing reefs.

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Why Does North County Have So Much Trouble Retaining Sandy Beaches?

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  1. Why Does North County Have So Much Trouble Retaining Sandy Beaches? Southern California Beach Processes Study O’Reilly, Guza, Seymour, Flick, Yates, Thomas, et al Scripps Institution of Oceanography

  2. Island Sheltering Wave Refraction/Focussing “Hot Spots”

  3. Wave Climate : Oceanside Littoral Cell Alongshore Wave Climate Reconstruction Cross-shore Component Incident waves Alongshore Component CDIP Buoys

  4. Oceanside Littoral Cell: The “River of Sand” Wave-Driven Net Southward Sand Transport Sand Leaves Cell at Scripps Submarine Canyon

  5. Wave-driven Lagoon Sub-Cells Batiquitos Sub-Cell Moonlight Sub-Cell San Elijo Sub-Cell Fletcher Sub-Cell San Diegito Sub-Cell Penesquitos Sub-Cell Torrey Pines Sub-Cell

  6. 1. COASTAL LAGOON LITTORAL SUB-CELLS Waves refract over offshore sediment fan south of the lagoon entrance. Coastal Lagoon Cross-shore Transport 2. EROSION HOT SPOT Waves focus south of lagoon entrance eroding the coast, disrupting southward sediment flow, and moving sand offshore towards the sediment fan. Longshore Transport Ocean Ocean 30m shoreline 3. The disrupted net longshore transport rate increases between lagoons resulting in net longshore erosion of sand. Incident waves drive net southward sand transport between lagoons. 20m depth contour 4. Coastal Lagoon Ocean The net longshore transport rate decreases rapidly to near zero in front of the lagoon, resulting in deposition of sand. Ocean 5.

  7. COASTAL LAGOON LITTORAL SUB-CELLS Coastal Lagoon Sand Borrow Sites Sand feeder site to maximize residence time in lagoon cell? Ocean Ocean Naturally sand-deprived section of coast along base of cliffs between lagoons? 20m depth contour Natural clogging of lagoon entrances? Coastal Lagoon Ocean Ocean Natural Erosion Hot Spot. Artificial surfing reefs to reduce erosion & cross-shore sand loss? Sand Borrow Sites

  8. Conclusions • We have no conclusions! • We do have new ideas, models, and data. • We think it is an appropriate time to begin sharing our SCBPS research with SANDAG on a routine basis.

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