Forecasting Subtidal Water Levels and Currents in Estuaries: Assessment of Management Scenarios

Abstract

Floods are one of the most harmful extreme events that occur in estuaries, which are induced by tides and freshwater discharges. The Guadalquivir River Estuary (SW Spain) has experienced multiple flooding events in recent decades. High-resolution time series from a long-term monitoring campaign were analyzed to assess the impacts of subtidal water levels and currents in this estuary. An autoregressive approach, which is considered as the nonstationarity of the freshwater discharge, indicated that water levels were well described by the linear superposition of levels induced by tides and freshwater discharge, whereas a nonlinear relationship between both tides and freshwater discharge reproduced the subtidal currents better. The obtained relationships were used to assess, on a medium-term basis, the effects of the expected 15% reduction in freshwater discharges and the planned 23% deepening of the navigation channel. The comparison among the results from four different scenarios based on these modifications and the present conditions of the estuary revealed that (1) subtidal levels will decrease when the freshwater input is reduced and (2) subtidal levels will be more harmful during extreme events due to channel deepening.