Numerical Study on the Impact of Coast Engineering on Water Environment in Hangzhou Bay, China

Hangzhou Bay, China, is a macro-tidal funnel-shaped estuary with highly turbid water. The width of the bay decreases from about 100 km at the mouth of the bay to about 8 km at Jianshan Station, within about 100 km distance. An FVCOM-BBL sediment model was built and fully calibrated for the macro-tidal turbid Hangzhou Bay to study the sediment dynamics and impact of coastal engineering on sediment dynamics in the bay. Model results show that SSC values were smaller near the north bank than those near the south bank. During spring tides, SSC values were about two times of those during neap tides. The net sediment fluxes, averaged over a spring-neap tidal cycle, were largely seaward at the shallow water area and landward at the tidal channel at Ganpu section. Tidal pumping contributes to the landward sediment fluxes, while Eulerian velocity dominated the seaward sediment fluxes. Tidal flat reduction increases landward and southward sediment fluxes through tidal pumping effect. Tidal flat reduction modulates sediment dynamics by changing tides, while local resuspension plays a small role. Careful planning must be paid to any proposed coastal engineering, which artificially makes changes to tidal flat in estuaries worldwide.