I am working on modeling surface run-off due to a rain event (e.g., 5 year rain for a duration of 30 mins.) over an approx. area of 30 km2 for which I have a DEM and necessary soil as well as land-cover data (Manning's n values). I am going to implement Green-Ampt infiltration model in ArcGIS 10.2 (with Python scripting) and have already computed rasters like flow direction, slope, flow accumulation, stream network, stream length, etc. with hydrology tools.
At each time-step, I have an excess water depth raster and velocity raster (with slope raster from slope tool) at each cell with which I can calculate the discharge volume that is flowing out from a cell to its neighbor. Now, my problem is:
- For the next time-step I have to add those discharge volumes to the corresponding cells to ensure mass balance but how can I determine to which neighboring cell is the discharge flowing? I only know that ArcGIS is calculating the steepest gradient for each cell but how can I ascertain which out of 8 neighbors does that gradient correspond to?
- For a time step and a cell, how can I define a run-off water depth?
Is it simply
(outflow volume - inflow volume)/area of cell?