Impact of Estuarine Dams on the Estuarine Parameter Space and Sediment Flux Decomposition: Idealized Numerical Modeling Study

초록

Estuarine dams are constructed for securing freshwater resources, flood control, and improving upstream navigability. However, their impact on estuarine currents, stratification, and sediment fluxes is not well understood. To develop a general understanding, an idealized modeling study was carried out using the COAWST modeling system. Idealized estuarine geometry was based on 10 estuaries with estuarine dams located near their mouth. Tide and river forcing were varied to produce strongly stratified, partially mixed, periodically stratified, and well-mixed estuaries. Each model ran for 1 year. Next, the models were subject to the construction of an estuarine dam and run for another year. Then, the predam and postdam conditions were compared. Results showed that estuarine dams can amplify the tidal range and reduce the tidal currents. The postdam estuaries tended to be salt wedge, strongly stratified, partially mixed, or periodically stratified types during freshwater discharge, but during no freshwater discharge they became fjord, bay, periodically stratified, or well-mixed types based on the estuarine parameter space. For all estuaries, the estuarine turbidity maximum moved seaward, and the suspended sediment concentrations tended to decrease. While the depth changes depended on the estuary type, the surficial sediment texture shifted to being muddier for all types. In terms of sediment flux mechanisms, the estuarine dam increased the seaward river runoff for cases with strong river, and increased the landward tidal pumping for cases with strong tides. This study is one of the first to generalize the effect of estuarine dams to a range of estuarine types.

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