Analysis Of Beach Response Under Wave Loading In View Of Seepage

The coastal zone is the main area for humans' production and activities. The coastal development plays an vital role in the global economy, with the continuous development of the coast, global coast zone is severely eroding. However, many governments protect the beach by means of extracting groundwater, and it is based on the groundwater seepage influences on the sediment transportation and beach evolution. The traditional coastal dynamic studies are on the basis of no seeping beaches or ignoring the seepage effects on the permeable beach. So the studies of sediment transportation and beach evolution under seepage has theoretical significance and social value.A set of 2D wave flume experiments on a sandy beach were performed to investigate the hydrodynamic characteristics, whose research depth was 0.4m,0.45m and 0.5m and was exposed to cnoidal waves and solitary waves. We also studied the change of cross-shore beach profile, sediment grains gradation and pore water pressure distribution under the conditions of lowering the groundwater artificially and pipe seepage.The 1/10 simplex beach slope were influenced on two wave types and three experimental depth to change wave dynamic factors. By way of lowering groundwater level and pipe seepage, the process of wave propagation, the beach topographical change, sediment grains gradation and pore water pressure inside the beach were recorded and measured.The experiment results represented that the water energy onshore under lowering the groundwater was less than that in the conditions of natural seepage as the theoretical analysis of FFT and HHT. Under the cnoidal waves, the artificial seepage including lowering groundwater and pipe seepage increased the beach evolution when they were compared with the natural seepage. When the seepage pipe was located on the interface of land and water, the erosion is the most. The sediment particles offshore was fined under the pipe seepage. The average value of minimum pore water pressure increased more than maximum pore water pressure and then the seepage force resulting from artificial seepage accelerated sediment movement. Under the solitary waves, the seepage generated by lowering groundwater accelerated the sediment accumulation. Compared with the natural seepage, the groundwater head increased the beach's unsaturation degree, infiltration water restrained coarse particles' movement and the grains gradation on the depositing area onshore appeared local coarsening phenomenon.