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, fl oodcontrol, and improving upstream navigability. However, their impact onestuarine currents, stratifi cation, and sediment fl uxes is not wellunderstood. To develop a general understanding, an idealized modelingstudy was carried out using the COAWST modeling system. Idealizedestuarine geometry was based on 10 estuaries with estuarine damslocated near their mouth. Tide and river forcing were varied to producestrongly stratifi ed, partially mixed, periodically stratifi ed, and well-mixedestuaries. Each model ran for one year. Next, the models were subject tothe construction of an estuarine dam and run for another year. Then, thepre- and post-dam conditions were compared. Results showed thatestuarine dams can amplify the tidal range and reduce the tidal currents.The post-dam estuaries tended to be salt wedge, strongly stratifi ed,partially mixed, or periodically stratifi ed types during freshwaterdischarge, but during no freshwater discharge they became fjord, bay,periodically stratifi ed, or well-mixed types based on the estuarineparameter space. For all estuaries, the estuarine turbidity maximummoved seaward, and the suspended sediment concentrations tended todecrease. While the depth changes depended on the estuary type, thesurfi cial sediment texture shifted to being muddier for all types. In termsof sediment fl ux mechanisms, the estuarine dam increased the seawardriver runoff for cases with strong river, and increased the landward tidalpumping for cases with strong tides. This study is one of the fi rst togeneralize the effect of estuarine dams to a range of estuarine types.