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Study on Spatial Distribution of Hydrological Information and Human Impact in the Watershed

Author: ShiHaiYun
Tutor: WangGuangQian
School: Tsinghua University
Course: Hydraulic Engineering
Keywords: Digital Watershed Model Potential evaporation Rainfall Spatialdistribution Human impact
CLC: TV12
Type: PhD thesis
Year: 2013
Downloads: 14
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Abstract

Watershed simulation is one of the major approaches for studying the natural lawsof water and sediment, solving the practical problems of hydraulic engineering, andraising the level of watershed management. And it is also the core and foundation ofdigital watershed. As one of the most important tools for watershed simulation,distributed watershed models have played a major role in the studies of the key anddifficult issues (e.g., the human impact on the processes of runoff and sediment).However, it is still important and necessary to develop methods for improving theaccuracy of watershed simulation. Based on the Digital Watershed Model (DWM), thisstudy developed the new methods for computing the spatially distributed potentialevaporation (PE) and rainfall; and meanwhile, this study quantitatively researched thehuman impact on the processes of runoff and sediment.A new method for computing the spatially distributed PE, including the modifiedDalton model and the functions for extending meteorological variables, was proposed,which would be useful to provide the more accurate PE inputs for the DWM. First, inorder to compute the PE for a single point, the Dalton model was modified by includingthe influences of the related meteorological variables. Second, through analyzing theimpacts of elevation on the related meteorological variables, the functions for extendingthe meteorological data recorded at a station to any given altitude were developed; andthe inverse distance weighting (IDW) method was applied to integrate the extendedmeteorological variables. The new method would be valuable for computing the spatialdistribution of the PE over regions with steep terrain and sparse meteorological stations.A new method for computing the spatially distributed rainfall through merging theraingauge measurements and the satellite observations was proposed, which would beuseful to provide the more accurate rainfall inputs for the DWM. Considering thetopographic influence on rainfall, a method for the satellite observations downscaling byusing the Digital Elevation Model (DEM) data was developed. Considering the effectiveinfluence radius of a rain, the above two rainfall data were merged by using the IDWmethod. The new method could integrate the advantages of the two rainfall data and would be valuable for computing the spatial distribution of rainfall over regions withsteep terrain and sparse meteorological stations.The methods for computing the spatially distributed PE and rainfall were proved tobe helpful to improve the accuracy of watershed simulation. However, in some regionswith considerable land use change, the impact of soil and water conservation measures(e.g., check dams and reservoirs) could not be ignored. And therefore, this studyquantitatively analyzed and modeled the human impact (e.g., check dams) on theprocesses of runoff and sediment. First, change characteristics of the processes of runoffand sediment as well as the causes were analyzed, and periods of natural state anddisturbed state were defined. Second, the amount and spatial distribution of check damswere given, and the topological relationships between check dams and river reacheswere established. Third, the maximum impact of check dams was evaluated, consideringthe situation that water from upstream was completely intercepted by check dams.Fourth, the relationship between check dam construction and the spatial distribution ofrainfall was analyzed, which would be useful for the decision making of the future soiland water conservation measures in such regions.

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