大河三角洲河口海岸演化机理模型研究:(I)模式理论与进展

Researches on dynamic model and numerical simulation of the large-scale estuarine shoreline evolution: (I)model theory and progress

从水沙通量变化对大河三角洲河口海岸建造及地貌演化的影响机理角度 ,通过研究目前国际上普遍采用的统计模型、几何模型、沉积动力学模型 ,以及数值模拟模型四种方法在建立大河三角洲河口海岸演化机理模型研究中的各自特点和不足 ,提出了建立宏观尺度机理模型的初步设想 ,并对运用Lagrange余流建立海岸演化机理模型所涉及的余流场的尺度转换、总余流场的建立和表达、用长期余流场构建泥沙起动、输运和沉积条件模式以及一线模型与三维动力模式耦合等关键性问题 。

The mechanism of long-term shoreline evolution of large-scale estuarine deltas under conditions of water and sediments flux changes (WSFC) is one of the hot topics of current global change research. In case of the Yellow River delta, the WSFCs are considered to play an important role in the evolution of delta because the river flow has been broken off for several times since the 1970s,which has changed the estuarine shoreline greatly. So it is urgent to analyze the modern the Yellow River delta and its adjacent area quantitatively and carry out in-depth studies on the mechanism of dynamic balance between the erosion and extension of shorelines under different water and sediment fluxes conditions in order to strengthen the theoretical basis of the delta's sustainable development. To reach that point, the mechanism of dynamic balance between erosion and accumulation under different water and sediment fluxes should be found. At present there are usually four kinds of models available to simulate the estuary shoreline formation and geomorphologic evolution of the great river deltas, which are statistic model, geometric model, depositional dynamics model and numerical model. The first two models do not describe the mechanism, and they can't be used to explain the long-term evolution of a great river delta coast; and the other two models can only compute critical values of the sediments' starting-up, transporting, and sinking processes in the very short cycle, although they can explain the mechanism in some ways. Therefore, there is still lack of mature theory on the mechanism of long-term templral (over one year) and macro spatial (the whole great river delta and its adjacent area) shoreline evolution modeling.After analyzing eroding and depositing processes carefully, we found it is necessary to conduit an in-depth study on the near-shore residual current dynamic process under conditions of the River's WSFCs, for Lagrange residual current is the key dynamic factor not only for discharging sediments long-term transportion but also for coastal and seabed's erosion and deposition. Finally the paper puts forward a tentative plan on building a macro mechanism model and offering a solution to the key problems including scaling scale, building and expressing total residual current field, and computing critical values of the sediments' resuspension, transportation and deposition.