Natural Indicators of Estuarine Sediment Movement

Natural sediment indicators are used in Yaquina Bay, Oregon, to show that marine sands enter the bay and move six miles up the estuary. Sediment texture and composition indicate that marine sands from the adjacent ocean beaches and near-shore areas are transported into the estuary by strong tidal currents or by wind. The amount of material transported up the estuarine channel decreases according to the decreasing flood current velocities. Yaquina River sands are trapped within the bay, and suspended silts and clays are deposited on tidal flats or carried to sea on the ebb tide. The extent, magnitude, and rate of deposition within and adjacent to the estuary are influenced by four factors: direction of littoral drift, river runoff, type of estuarine system, and wind direction. These factors dictate that maximum transportation and deposition of sediments occur during the winter and spring; during summer and fall sediment transport and deposition are at a minimum.