South Yellow Sandbank In The Edge Region And The Driving Mechanism Of Evolution Layout Of Reclamation

Inner part of radial sandbanks (IPRS) is the convergent region of tidal systems in the South Yellow Sea. The continuous growing of tidal flat provided large using potential of coastal space resources. The frequently swings of tidal creeks induced the changes between scouring and silting greatly. Research on the driving mechanism of geomorphological evolution can support the reclamation in the complex dynamic environment of the IPRS. Hydrological data、topographic data^and remote sensing images in radial sandbanks were collected and systematically analyzed, and were integrated in the geo-database built. Combined with previous research, this paper carded and analyzed the macro evolution background and dynamic pattern of radial sandbanks, studied the driving mechanism of geomorphological evolution of IPRS with numerical simulation, remote sensing and GIS techniques. Based on the tidal flow mathematical model of IPRS, the principles and layout schemes of reclamation of IPRS were studied and proposed.(1) Based on the remote sensing images of1973-2013and the topographic data, this paper analyzed the characteristics of macro evolution and recent developments of "water channel-sandbar system" with GIS techniques from different perspectives. The evolution characteristics of "water channel-sandbar system" performed as the following aspects:The basic combination form of "water channel-sandbar system" was at the status of stability. The scale of tidal flat remained relatively stable with the current situation of inside part silting while external part washed. Tidal channels close to the shore were moving towards coast. The north part and the south part differ in the forms and the evolution trends。(2) The evolution characteristics of "water channel-sandbar compound system"(IPRS) performed on these aspects:The inner part kept prograding and the swales were highly variable. The north-south tidal channels of inner part exist for a long time and the main channel changed from one to another. The combination situations of channels of inner part in recent years shown the prograding of Gaoni, the north toward moving of Doufuzha and the north-south connection of Dongdagang and Xidadang.(3) Since1970, the evolution of IPRS could be divided into four stages:1970s-Chenjiawu period (integrated sandbanks),1980s-the relative balance period, 1990s-Xidagang period, after2000-Dongdagang period.(4) The understandings of evolution mechanisms on IPRS:IPRS was the convergent region of the two tidal systems, where turbulent change was its main characteristics. The existence of north-south tidal channels was stable in IPRS. The north-south tidal channel in the tail of Chenjiawucao was gradually silting with the Gaoni expanding. The innate character of the Dongdag and Xidagang’s evolution was the westward of north-south main channel. With the stability of the external environment, the general characteristics of IPRS was the sustained existence of north-south tidal channels and the dynamically changes of branch tidal creek system.(5) Although IPRS has the largest sandbanks, its hydrodynamic environment is complicated, due to the feature of tidal flow convergence zone. The tidal flat reclamation layout should adapt to the trend of dynamic field, so as to maintain stability of the existing tidal power pattern. The basic principles of layout in IPRS were the follows:maintaining the north-south tide channel, reserved the "split point areas" of channel, avoiding the swinging zone of Xidagang.(6) Based on the reclamation principles of IPRS, eight schemes for two kinds of reclamation spatial layout were proposed. According to the analysis of response for tidal power and flux between the two kinds of schemes, the small-scale of block-layout was recommended. Due to the stability of tidal flat and the tidal creek systems changes, the reclamation areas of Beijianzi and Gaonibei were the priority areas. At the time the reclamation demand is not significant, the reclamation area of Gaoninan was the restricted area for its complexity of tidal flat and the tidal creek systems.