On Thu, Jul 21, 2011 at 3:30 PM, frans-joost <[email protected]> wrote: > Dear GRASS users, > > I'm trying to implement the Morgan Morgan Finney model for erosion > estimation. > One problem I'm having is with the accumulation of surface runoff. > Is it possible to sum all cells that are uphill, meaning each individual > cell has an amount of water that flows downslope. > It should be possible to use a flow direction map to accomplish this.
Flow direction is usually an output, not an input for hydrological modeling. At least in GRASS, r.terraflow and r.watershed take elevation (plus other optional parameters) as input and produce amongst others flow accumulation and flow direction as output. > > r.terraflow does not have an option to accumulate using another map > r.watershed gives me very high and negative values (not sure what happened > there) r.watershed flow accumulation output [0]: The absolute value of each cell in this output map layer is the amount of overland flow that traverses the cell. This value will be the number of upland cells plus one if no overland flow map is given. If the overland flow map is given, the value will be in overland flow units. Negative numbers indicate that those cells possibly have surface runoff from outside of the current geographic region. Thus, any cells with negative values cannot have their surface runoff and sedimentation yields calculated accurately. Markus M [0] http://grass.osgeo.org/grass64/manuals/html64_user/r.watershed.html _______________________________________________ grass-user mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/grass-user
