| The latest dynamic of erosion/deposition change of seabed will provide reference for the construction of coastal engineering and offshore harbor nearby. The adjustment of erosion/deposition rate after the construction of harbor is significant to the normal operation of harbor and channel. The Abandoned Yellow River Delta (AYRD) has long been erosion process since 1855 when the Yellow River runs into the Bohai Sea. If harbor locate at coast which is being erode, it definitely cause a series of questions. And now, the breakwaters have been constructed at the projecting part of the AYRD, and coastal environment has been adjusted due to the construction of breakwaters. Therefore, research the erosion/deposition change around the breakwaters in normal and extreme weather conditions is significant to maintaining and operating harbor.This paper used bathymetry measured at 7/2007 and 8/2012, before/after the construction of breakwaters and bathymetric sections of different times to analyses the erosion and accumulation characters of the AYRD before/after the construction of breakwaters of Binhai harbor. Based on bathymetry, hydrometeorology and surface sediment and so on, the current model, wave model and sediment transport model are building. Combined with erosion and accumulation character, the causation of geomorphology change of the AYRD was analyzed. The results show that:Before the construction of breakwaters the erosion rate of the AYRD was decline, and the seabed exceed -15m was tend to stable. After the construction of breakwaters, in the exterior of harbor, the root and head area of breakwater erode seriously, and the erosion depth exceed 2m. The north of breakwater eroded unitary, where the corner areas erode slightly relatively, and the erosion depth is 0.5m approximately. While the middle areas of south breakwater accumulate. The deposition thickness is 1m. In the interior of harbor, the shallow water zones eroded, and the other areas accumulate. The accumulate center locate the middle area of north breakwater and the maximize thickness is 5m. In the exterior of harbor, the seabed has been eroded, the erosion thickness is 1.6m and heave and hollow on the seabed were smoothed.The flow model’s simulated results show that:after the construction of breakwaters, the tide current in the scale of 10km around the breakwaters increase above 0.2m/s, where the head area of breakwater increase more than 0.8m/s and reach to 2.2m/s and the ebb increase more than the flow. While, in the interior of harbor, imported by the burble around the head area, tidal current reduced to 0.3m/s, and the main movement of tide current is anticlockwise circulation.In the exterior of harbor, the wave height increase at the root and head areas of breakwaters. In the interior of harbor, the wave height decrease and wave distribute the south area closed with the south breakwater, and the north area is the wave shadow zone.After the construction of breakwaters, suspend sediment net transport into the inside of breakwaters. The net suspend sediment flux to the inside of breakwaters in one tide period is 8.5 x 103 kg/m.Based on the couple modeling of the tidal current model and wave model, the sediment transport model is used to simulate the evaluation of erosion and deposition of seabed. The analysis show that:wave is the main force causing erosion at the shallow water zone exterior of harbor and sediment transported by current. Current is the main force causing erosion at the head area of the breakwater. In the interior of harbor, wave is the main force causing erosion at the shallow water zone. In the harbor, the accumulated sediment is 4×06m3 per year. The accumulated sediment in the harbor mainly comes from the open sea.In the extreme weather conditions, at the shallow water zone where shallow than -6m eroded and the maximum erosion depth is 1.5m, and at the submarine where water depth between -6m and -10m accumulate and the deposition thickness is 0.5m. |
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