Distributed Hydrologic Modeling
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Distributed Hydrologic Modeling
Distributed Hydrologic Modeling B AXTER E. V IEUX School of Civil Engineering and Environmental Science, University of Oklahoma, Norman, OK, USA Synonyms Spatial hydrologic modeling; GIS-based hydrology; Hydrogeology; Hydrology Definition Distributed hydrologic modeling within a GIS framework is the use of parameter maps derived from geospatial data to simulate hydrologic processes. Distributed models of hydrologic processes rely on representing characteristics of the earth’s surface that affect components of the water balance. Capturing the natural and human induced variability of the land surface at sufficient spatial resolution is a primary objective of distributed hydrologic modeling. Geospatial data is used to represent the spatial variation of watershed surfaces and subsurface properties that control hydrologic processes. Geospatial data is used in hydrologic modeling to characterize terrain, soils, land use/cover, precipitation, and meteorological parameters. The use of Geographic Information Systems is now commonplace in hydrologic studies. General purpose GIS software tools can be used for managing and processing spatial information for input to hydrologic models. Development of sophisticated GIS software and analysis tools, and the widespread availability of geospatial data representing digital terrain, land use/cover, and soils information have enabled the development of distributed hydrologic models. Historical Background Mathematical analogies used in hydrologic modeling rely on a set of equations and parameters that are representative of conditions within a watershed. Historical practice in hydrologic modeling has been to setup models using one value for each parameter per watershed area. When the natural variation of parameters representing infiltration, hydraulic roughness, and terrain slope are represented with a single parameter value, the resulting model is called a lumped model. Many such models, termed conceptual models, rely on regression or unit-hydrograph equations rather than the physics of the processes governing runoff, soil moisture, or infiltration. In a distributed modeling approach, a watershed is subdivided into grid cells or subwatersheds to capture the natural or human-induced variation of land surface characteristics. The smallest subdivision, whether a grid or subwatershed, is represented
Distributed Hydrologic Modeling, Figure 1 sentation
Subwatershed model repre-
Distributed Hydrologic Modeling, Figure 2 Gridded representation with flow direction indicating the drainage network
by a single value. Subgrid variability can be represented by a probabilistic distribution of parameter values. Figure 1 shows a subwatershed representation, whereas, Fig. 2 shows a gridded drainage network traced by finite elements laid out according to the principal flow direction. Whether a lumped or distributed approach to hydrologic modeling of a watershed is taken, GIS and geospatial data play an important role in characterizing the watershed characteristics. The
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