Evolution of the abandoned Shenxiangou-Diaokou delta lobe:processes and mechanism

The modern Huanghe delta has been created owing to the rapid accumulation of a huge amount of sediment originating from the Chinese Loess Plateau since 1855.After 1976 the end river channel shifted southeastward from the Diaokou course to the Qingshuigou course,and the abandoned Shenxiangou-Diaokou delta lobe was eroded back remarkably,as indicated from the bathymetric data of 1976-1990.A wave climate modeling over the modern Huanghe delta indicates that the nearshore wave action is the major driving force for the deltaic erosion since the distribution of wave-induced bottom shear stress is spatially coinciding well with the deltaic erosion off the abandoned Shenxiangou-Diaokou delta lobe.The northeastward protuberant topography of the abandoned Shenxiangou-Diaokou delta lobe leads to a convergence of wave energy in the shallow coastal region where the water depth varies from 4 m to 10 m.Both the wave energy releasing and induced high bottom shear stress in the shallow area result in significant local sediment resuspension,which produces a highly turbid zone off the abandoned delta lobe as indicated by the field observations and satellite images.As a result of wave actions over decadal time scale,the subaqueous delta slope has been reshaped into a gentle profile quite different from the previous one before 1976.In addition,there is a large discrepancy between the surface sediment compositions in shallow coastal area and deep area,which could be an indicator for the transport pathway of the resuspended sediment.This study thus presents an illustrative example to the active delta lobe since the water and sediment discharge from the Huanghe to the sea has been decreased steadily during the last 50 years.