Effect of Estuarine Dam Location and Discharge Interval on Estuaries

초록

Estuarine dams are dams constructed within the salt or tidal intrusion limits of estuaries for reasons such as securing freshwater resources or flood control. Unlike tidal weirs, which operate by freshwater overflow, estuarine dams operate by discrete freshwater discharges via sluice gates. Due to the complexity and diversity of estuaries, the effect of estuarine dams on estuarine physical and geological processes is not well understood. Previously, the effect of an estuarine dam located near the mouth for a range of estuarine types (i.e. strongly stratified, partially mixed, periodically stratified, and well-mixed) under pre- and post-dam conditions has been studied using the COAWST model (Figueroa et al., 2022). However, the effect of different dam locations and freshwater discharge intervals has not been studied. Here, models were run for each estuary type where the dam locations were specified at 20 km, 55 km, and 90 km upstream from the mouth, and the discharges intervals were specified as once every 0.5 days, 3.0 days, and 7.0 days. The results were analyzed using the estuarine parameter space, a sediment flux decomposition, and an analytical tidal model. During discharges, estuaries shifted toward more stratified types, whereas during no discharge, the estuaries shifted to more mixed or bay-like types. Estuaries with large river discharge tended to shift from landward to seaward sediment fluxes. Estuaries with large tides tended to show the opposite trend. This was due to the shift from continuous to episodic discharge and mixed to standing tides, respectively. The dam location mostly affected the cases with strong tides due to the effect of resonance and the Stokes return flow reduction upon shift from mixed to standing tides. The discharge interval mostly affected the cases with strong river. This was due to larger discharge intervals having a greater hydraulic head, seaward discharge pulse, and frontal behavior compared to the pre-d