A procedure to define the optimal grid size for the exhaustive extraction of hydrologic waterished drainage features from a digital elevation modle using a raster geographic information system

摘要

To study the fate of non-point source pollution and other spatial environmental management porlgmes, it is very conventent to generate and to exploit a synthetic representation of the watershed describing the terrestrial and riverine transportation paths of water and contaminants under the action of gravity within a watershed. In raster mode, a drainage algorithm called D8 is often used to identify the flow direction (aspect) from each cell to one of the eight adjacent ones according to the steepest elevation gradient and then to generate the flow accumulation defining a synthetic hydrographic network. Given a specific digital elevation model (DEM), two parameters need to be optimized; firstly, the size of the grid allowing the extraction of all the relief information contained in the available DEM; secondly, a basic unit area necessary to induce a perennial stream, and thus control the density of the generated hydrographic tree.