Runof97: a GIS-based, Distributed, Surface - Runoff Model
Runof97 is a fully distributed Geographic Information System (GIS)-based surface runoff model. The model was built to assist the Daisy Lake Watershed Restoration Project. Daisy Lake and its surrounding watershed, located near Sudbury, Ontario, have been adversely affected by local mining practices, resulting in a severely denuded landscape, and acidic lake and soil conditions. The restoration project is studying the effectiveness of watershed liming to improve runoff water quality.
By simulating overland flow, Runof97 will develop a better understanding of water/lime contact time on different surfaces, and will determine surface runoff velocities to assist with erosion studies, to help assess the degree of reforestation required to slow erosion, and to assess how lime of different grain sizes is redistributed. The model employs a block-centred, finite difference approach to solve its governing equation. The governing equation is an adaptation of the Manning equation for surface flow, and includes surface slope, surface roughness, and depth of water flowing over the watershed at any given time. Runof97 is capable of simulating varying rainfall intensity and infiltration rates during single storm events. The model accepts IDRISI images as input.
The model was tested by comparing simulated and measured hydrographs at the outlet of the watershed for a small storm. The model simulated the timing and volume of two early peaks in the measured hydrograph. A third peak was not simulated but the peak probably results from interflow, which Runof97 does not address. Secondary purposes of the model are related to the visual capabilities of GIS. These include using the simulated surface water depth maps to test Digital Elevation Model (DEM) integrity, and the development of a “movie” of surface water flowing down the watershed. This dynamic visual display provides a more intuitive knowledge of water movement over the landscape.
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