Erosion Mechanism And Process Of The Intense Erosive Coast Of Yellow River Delta

Since the diversion of the Yellow River from DiaoKou river flow path in 1976, with the effects of marine dynamics, the intense erosive coast of Yellow River delta (YDR) suffered serious erosion, such as shoreline retrograde or slope instability. It resulted in the great amount loss of land resources and biological habitat. It had threatened the coastal artificial facilities and oil production.This paper presents a data-based study of waves, currents, sediments and submarine topography by applying spatial analysis and mathematical statistics analysis, in order to understand the process and mechanism of coastal erosion on the intense erosive coast of YDR from sediment distribution characteristics, erosion-deposition variation and hydrodynamic action. The results are shown as follows:(1) Based on the spatial analysis of ArcGIS softwares, the sediments type distribution map and average diameter distribution map were draw. It was silt-dominated components in the intense erosive coast of YDR.With the decrease of percent of sand and the increase of percent of clay, average diameter become finner gradually from shore to sea. Seadiment types exhibited a variation gradient as sand, silty sand, sandy silt, sand-silt-clay, clayey silt. Within 18m depth the sediment types and average diameter incline to coarse, outside a finner.The intertidal sediments were mostly silt, sand content was high, and clay content rarely. With the increase of percent of sand and the decrease of percent of clay, average diameter became coarser gradually from shore to sea.This paper analysises the sediment gain size parameters of intense erosive coast of the YDR. It's mainly finner particles, poorly-sorted, forward-bias and wide tip type. With average diameter finner, sorting coefficients poorer, skewness reduced, and kurtosis reduced, too. According to Cao-Collins grain size trends model, sediment transport trends in this area mostly dominated by offshore residual currents, they showed mostly offshore transport trends. From the Fleming ternary diagrams, the hydrodynamics of research region is strong generally, the horizontal intertidal zone> shallow water zone> deep water zone, vertical Dongying Port nearshore> Feiyantan nearshore> Gudong near shore.(2) The intense erosive coast of YDR had shown an erosive characteristics change, from severe erosion gradually to slow erosion. The coast under the artificial control of stability also suffered serious erosion in the nearshore.Based on the analysis of ArcGIS software space analysis module and 3D analysis module, the results showed erosion area slightly less than the siltation area, the erosion were more intense. Erosion area around the cylindrical arc-shaped distribution in the intense erosive coast within 15m depth,2m～12m depth of erosion is particularly serious, where formed three erosion centers. As a whole, erosion rate decreased, erosion-deposition variation had shown a periodic change as erosion, deposition, balance, deposition and erosion.Comparison of the typical profile of the historical data showed the upper parts of profile erosed, the lower parts silted in the intense erosive coast of YDR. The erosion-deposition coversion often occurred on 12m～14m of the profile. The difference of erosive intense and depositive intense resulted in the variation of erosion-deposition coversion in the profile. The profiles of Gudong nearshore had erosed within 12m after 1990.Because of accumulation time, shoreline direction, amphidromic point and sediments from Huanghe river, the balance depth was the most deepest in Dongying Port nearshore, the balance depth on both sides was reduced gradually.(3) The intense erosive coast of YDR suffered seversed erosion by the effects of marine dynamics. It often be the local wave by wind, northerly wave was constant wave and strong constant wave. Higher waves can stir up the sediments in the deeper depth, the frequency of stirfing up sediments by wave was decreased from shore to sea. By the effects of stirring up sediments characteristics, gain size finner, sediment types changed as sand, silty sand, sandy silt, sand-silt-clay, clayey silt from shore to sea. As the erosive intense reduced with depth increased, the serious erosion part of profiles was broadly consistent with wave effect range.The longshore tidal level changed as saddle shape by the existence of amphidromic point. The flow velocity was higher near the amphidromic point, the profile surfered intenser erosion, the banlance depth was deeper. There were significant differences of currents between both sides nearshore of amphidromic point. When the velocity was high enough, the currents could stir up sediments in the nearshore west to amphidromic point. However, in the south, the currents could not.The residual current velocity was lower in research zone. It mostly be residual current by wind, the direction was mainly offshore. It's important for the transport of sediments and profile topography. The erosion-deposition variation in the intense erosive coast of YDR may be related to the effects on coast profile by the storm surge.