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<p>Morphological changes to beaches are the result of sediment transport via wind forcing, water flow, and human interference. Extreme morphological change to beaches occurs when a breach occurs across a beach. Each year, an ephemeral river breaches Carmel River State Beach (CRSB), a pocket beach that separates Carmel Bay from Carmel River, after lagoon water levels reach a certain height. Some seasons have a breach located constantly at the southern end of CRSB. During other years, the river breach migrates to the north throughout the season prior to relaxing to the south for breach closure. Using aerial photography and Structure from Motion photogrammetry, this study investigates the seasonal movement of the ephemeral river channel across the beach, the effects of wave height and direction on the morphological changes observed, and the overall net transport of sediment involved from December 2016 to June 2018. CRSB was found to be a closed system of sediment transport due to alternating migratory and stationary breach seasons. Migratory years cause beach erosion while stationary years yield sediment accretion or beach building, creating a stabilizing effect on the long-term sediment balance of CRSB. Findings suggest that river breach migration at CRSB is influenced by river discharge levels and local wave climate. In the wave climate at CRSB, there are slight seasonal variations in wave direction that result in enhanced northward momentum during migratory years.
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<br>Subjects: Carmel; beach morphology; breach; river; wave height; topography; SfM; Structure from Motion; Carmel River State Beach; aerial photography; photogrammetry; migratory; river discharge</div>
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Coughlin, Jillian N.</div>
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