Study Of Variation Features During Coastal Erosion Processes On The Abandoned Huanghe River Delta And Integrated Protection Measures

The historical evolution tendency of North Jiangsu coastline is one of the hot spots on the field of coastal dynamic geomorphology in China. As far as a long-term regional coast evolution is considered, the appearance of local variance during the course of intensive erosion on the Abandoned Huanghe River Delta Coast since 1855 is equally noteworthy. In the past one and a half centuries, due to the absolute losing of sediment supply from the old Huanghe River, the Delta Coast was fearfully and continually eroded. Current coastline has been basically stopped from retreating by coast protection engineerings. Yet the beach and the submarine coast slope are still in eroding as before. Coastal changes during eroding, such as surface sediment coarsening and profile steepenning, indicate a tendentious change of coast nature from muddy to sandy is in vogue. However, a comprehensive discussion on coast nature variation is almost absent previously. And the existing protection engineerings are mostly aimed at sandy coast erosion. Take coast variation as a handhold, the paper worked over the erosion and the concomitant variation of the coast, to explore the mechanism of variation during erosion, so as to support effective measures for coastal protection, covered following aspects:â‘ Based on historical recordations and approved research productions of the coast evolution in North Jiangsu, variation of coast nature during the course of eroding caused by the migration of the lower reach of the old Huanghe River was discussed, namely the transition processes between sandy and muddy coast;â‘¡Integrated field investigations, sediment sampling and analyses, coastal dynamic and sediment environment analyses, comparison among submarine landforms and coastal profiles of various time phases, comparison of coastlines from remote sensing images of various phases, calculation of suspended sediment concentration from remote sensing data, are employed to clarify the phenomenon and course of variation arisesed during coast eroding; â‘¢ Based on a wave-sediment physical model of the concave seawall coast stretch on the Abandoned Huanghe River Mouth, formation process of the stable bay during the variation of coast nature, origin of coarsened sediments, characters of the bay shape and so on were studied. Similarities and differences between bay shapes of variational and typical sandy coast were also analyzed, and responses of bay shape to wave energy on variational sandy coast are discussed by serial experiments of different wave conditions as well; And â‘£, according to the features of coastal variation, particularity of sediments and dynamic environment and course of formation of a stable bay concluded from previous study, applicability of employing headland control on coastal protection, and approaches of constructing an integrated protection system on the Abandoned Huanghe River Delta Coast are demonstrated.Concluded: â‘ The Abandoned Huanghe River Delta muddy coast is varying to a sandy coast currently. The course belongs to a conversed regulation of nature variation during coast progradation in the historical period; â‘¡Temporally and spatial diversities of dynamics and sediment transportation tendency is the mean cause of existing diversities of erosion. With the process of enhancing of wave dominance and enriching of coarsened sediment, the variation appearance tends to develop toward a wave dominated sandy coast on geomorphologic aspects; And â‘¢, the existing variation of the Abandoned Huanghe River Delta Coast during eroding made it possible for headland control to form stable bays, and provided a fresh approach to construct an integrated protection system.