Flow accumulation with weights

Discussion created by veronesf on Jun 27, 2012
Latest reply on Jun 28, 2012 by GSCUser85
I have a problem with Flow Accumulation.

I have a DEM, on which I indetified and filled sinks and calculated the flow direction. This works and gives me a raster with resolution 0.00833°.

Now I want to run Flow Accumulation with a raster for weight. My weight raster is a 0.5° raster with water uses from surface waters. In each pixel the amount withdrawn in that respective pixel is given. I now want to accumulate these withdrawals, becuase once I have withdrawn a certain amount in one cell, this amount is ging to miss in the downstream river as well.

I re-calculated the raster to have the same resolution like the flow Direction raster (by multiplying with the area of the 0.00833° cells and dividing with the area of the 0.5° cells and then mosaic to the lower resolution).

The tool also runs but to me the results seem unrealistic: I get values up to 10^13 m3/yr, while I had in the original raster values of maximum 10^8. Is that possible?
I checked with rivers in the area and they have runoffs of around 10^10 m3/yr. That would mean my rivers run dry, which is not the case in reality.

Does anyone know what I am doing wrong?
Thanks a lot!