Hyperpycnal River Plumes - an opportunity to study their transport and deposition in a controlled dam-removal experiment

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Hyperpycnal (high density) flows coming directly from the rivers and continental-shelf fluid muds are considered to control considerable cross-margin sediment transport but are difficult to study due to unpredictable nature of such large discharge events. Dam removal on Elwa River of the Olympic Mountains in Washington may allow the study of such events. Two dams will be removed over a 2-year period on the Elwa starting in 2011, during which time models predict turbidite formation and gravity flows (hyperpycnal plumes) in Juan de Fuca Straits. The PI will utilize this opportunity to study the high-density flows through real-time monitoring of suspended sediment in the rivers and offshore. They hypothesize that most of the sediment discharged soon after dam removal will move to relatively deep water as high density plumes move below the influence of waves and currents. They will study four specific river discharge conditions and the two peak discharges on Elwa will allow these conditions to be investigated individually.Hyperpycnal flows to the ocean have not been studied in any detailed before and the proposed work should bring new information on the role of these elusive events on the dispersal of sediment to the basins. The PIs plan to incorporate the work with some field based courses and will support one graduate student.