Reconstruction Of The River Network Structure In The Pearl River Delta Plain In The 1930s

The fifth IPCC Assessment Report noted that global warming will produce more and more serious adverse effects on coastal systems and low-lying areas. In the river downstream of the coastal plain region where economic and social development is highly advanced, good surface structure of rivers plays an important role in dealing with the regional extreme rainstorm disasters especially in the river downstream of the coastal plain region where economic and social development is highly advanced.Currently, the academic studies on river network have focused on the impact of human activities on the river system structure under the background of urbanization. The research on the river network structure in historical period has important significance and function in the river network structure research and the recovery of river regulation and storage function in the present coastal plain areas. Previous studies tend to be confined to the impact of large-scale human activities in the past five decades on the river system structure, which are inadequate in terms of a comprehensive grasp of the change process, leading to the human's current transformation of water networks, and the consequences that there are a lot of unknowns with the impact of urbanization on water network. Therefore, the cases in historical period must be studied (When human beings do not change the river system structure by the means of large-scale mechanical engineering), so that we can have a comprehensive and objective understanding of the influence of human activities on the river system structure under the background of urbanization.This study was based on CHINA Topographic Maps issued by U.S. Army Map Service in 1954,1:500000 Guangdong topographic maps made by Japanese Military Headquarters in 1938,1:25000 Guangdong topographic maps made by Japanese Military Headquarters in 1943, and Guangdong Provincial Hydrological Records, Guangdong Water Resources Annals and annals of counties in the research area and other graphic materials in the historical period. With the technology of GIS, methods like reconstruction of historical river morphology, grading scheme of historical river system and building a grid system and others are used to the reconstruction and rehabilitation of river network structure of Pearl River Delta in the 1930s. Alter obtaining the parameters and results of its river network structure and carrying on a preliminary analysis of the obtained findings, the research conclusion is as follows:1. Based on CHINA Topographic Maps by U.S. Army Map Service in 1954, 1:500000 Guangdong topographic maps made by Japanese Military Headquarters in 1930-1934,1:25000 Guangdong topographic maps made by Japanese Military Headquarters in 1930-1934, the restoration of Pearl River Delta's planar structure in the 1930s is implemented with high accuracy by the means of GIS technology. And reconstruction of historical river morphology and grading scheme of history river system are conducted to speculate the three dimensional structures of river network in the research area.2. By rebuilding the three-dimensional model of river network in the study area in 1930s, parameters of river system structure are quantitatively analyzed (including river drainage density, river rate and so on), the maximum capacity of river storage is calculated channel and a preliminary analysis is made.3. Agricultural development in traditional period has a close relationship with the formation of rive network of the Pearl River Delta in 1930s. At that time, the river network system is a common result by the natural development, agricultural fields and reclamation. The development of diked fields expanded the cultivated area in Guangdong Province and released the pressure of growing population. Thus, it objectively promoted the expansion of t river network.For nearly five decades, there are a lot of unknowns with the transformation of the water network by humans and the impact of urbanization on water network. This study, by studying the river network structure of Pearl River Delta in 1930s, combining the traditional historical documents and GIS spatial analysis, presents a historical geomorphology in a more intuitive way. By using reconstruction of historical river morphology, grading scheme of historical plain river, this paper summed up a set of research methods about reconstructing the three-dimensional structure of plain river network in historical period and how to calculate the maximum capacity of river storage. This can provide the basis for other studies on plain areas, help to evaluate the impact of human activities on the river system structure under the background of urbanization in a more comprehensive way, and attempts to provide support for the coordinated development of urbanization and river network.