SEDIMENT TRANSPORT ASSOCIATED WITH EPHEMERAL RIVER BREACHING AND CLOSING EVENTS
Young, Walter R.
Orescanin, Mara S.
Metcalf, Jeremy P.
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Breaching of beaches is a catastrophic morphological change that can fundamentally alter the circulation within littoral systems and create damage to surrounding coastal infrastructure. At ephemeral rivers with intermittent seasonal river discharge, rivers undergo breaching and closure events that result in significant morphological evolution, and to quantify this evolution, beach elevation must be measured through beach and bathymetric surveys. To better understand the volume, rate, and direction of the sediment transport, and to determine if the seasonal excavation to artificially breach the Carmel River State Beach to avoid flooding of adjacent residences to the river lagoon is necessary and effective, the breaching cycle was observed during the winter months of 2017-2018. The methodology of surveying the beach using Structure from Motion with an unmanned aerial vehicle (UAV) was utilized for the rapid beach morphology assessment with centimeter accuracy, which can be applied to future civilian and military operations even in remote and inaccessible areas or contested beaches. Digital Elevation Model analysis revealed that the sediment was primarily transported onto the back beach alongshore due to wave overwashing and the artificial breaching was ineffective in maintaining an open breach and caused a more-rapid outflow of the secondary natural breach, which could be harmful to indigenous aquatic wildlife and their habitat.
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