Influence of River Discharge and Dredging on Tidal Wave Propagation: Modaomen Estuary Case

Dredging and flow reduction in the Modaomen Estuary in China have had a measurable impact on tidal propagation and damping. This paper includes an assessment of the impacts of these human interventions through the use of a new analytical hydraulic model procedure. The model calculates tidal propagation and damping as a function of bathymetry and river discharge through a simple iterative procedure with explicit analytical equations. The results obtained are accurate and allow both an analysis of the historic development and a sensitivity analysis to assess the effect of possible further dredging and flow reduction. Particularly in the upper reaches of the estuary, tidal damping and wave celerity are sensitive to dredging and flow reduction. Historic analysis shows that due to these activities, since 1993, the tidal amplitude in the Modaomen Estuary has increased by more than 0.1 m, while the travel time of the tidal wave has decreased by 30 min in the middle part of the estuary and up to 80 min in the upper reaches. In the future, the tidal amplitude and the wave celerity will increase even further if flow reduction and dredging continue. Moreover, this development would increase the risk of salinization in the estuary and facilitate the inland propagation of storm surges.