Sediment Yield And Decision-making Support System For Soil And Water Conservation In Watershed With GIS

According to a GIS application model named "target-driven & data driven", both the planning and definition of DSS (Decision-making Support System) for a basin by target-driven, and the GIS operation processes by data-driven are discussed in this paper. In the planning and definition, for the specific target of scientific decision-making of soil and water conservation in watershed, the essence of soil and water conservation in a watershed is analyzed. After decomposing this notion, the concepts of soil loss modulus, soil load capacity, and man's future action index are derived. Further more, those concepts are analyzed to determine the factors for quantificational calculation according to the development and existing achievements of soil and water conservation. Based on above discussion, the fundamental data for MDSWC (Macro-Decision-Making for Soil and Water Conservation) in a basin are gained step by step.Focusing on MDSWC in a watershed, the rules and methods of database construction, the calculation methods of soil loss modulus, soil load capacity, and man's future action index have been discussed in the GIS operation processes, according to the gained data and the requirements of DSS for soil and water conservation in a basin. Further more, some methods of knowledge processes for decision-making model library, and some arithmetic in commonly used in MDSWC, are also been recommended in this part.Soil loss mechanism, the foundation and core of model library and knowledgelibrary in MDSWC, are also studied in this paper. According to observed data of Jianjia Gully in Yunnan province, Yufeng watershed in Sichuan province, and Zhuanyao Gully in Shanxi province, the function of antecedent precipitation in gradual sediment yield and abrupt sediment yield is preliminarily discussed from controlling factors view. The method of PCA (Principal Component Analysis) is applied to study the factors of sediment yield in order to understand the contribution of antecedent precipitation to the sediment yield of watersheds with different conditions of sediment supply. The result shows that antecedent precipitation is the main contributor of the second principal component and plays a minor role in gradual sediment yield in Yufeng watersheds and Zhuanyao Gully. However, it is the chief contributor of the first component and plays an important role in abrupt sediment in Jiangjia Gully. This is considerably important to dredge up antecedent precipitation to mitigate the hazards of abrupt sediment yield.Moreover, the temporal properties of annual sediment yield by debris flow at the Jiangjia Gully are also discussed from temporal viewpoint with mathematical method for periodicity analysis. In accordance with the observation data series from 1965 to 1998, a research and analysis concerning the quasi-periodicity of sediment per year yielded by debris flow at the Jiangjia Gully had been explored. As a result, a preliminarily conclusion was drawn that 6 years of periodicity for the peak value of debris flow sediment transporting exists.In according to software engineering thought, the common method for software development is introduced in the last part of the paper, then, the application in Yufeng decision-making support system for soil and water conservation is discussed in detail. Finally, the main functions of this system are briefly displayed.