Pre-Processing:Watershed Delineation and Grid Construction
The primary input files for a GSSHA rainfall/runoff simulation are the 2-D finite difference grid and its accompanying surface elevations. The grid is a rectangular area that covers the extents of the watershed. Individual cells whose centroid are within the watershed boundary are flagged as “active” (a value of “1” in the watershed mask), and cells outside the boundary are flagged as “inactive” (a value of “0” in the watershed mask). WMS can be used to automatically delineate a watershed boundary from digital elevation data and then construct a finite difference grid with the appropriate active and inactive flags set for individual cells.
In this chapter you will learn where to locate digital elevation data that can be used for automated basin delineation and assignment of surface elevations for the finite difference grid. You will also learn the basic processes used by WMS to delineate the watershed boundary and construct a grid.