topic Flow accumulation with weights in ArcGIS Spatial Analyst Questions https://community.esri.com/t5/arcgis-spatial-analyst-questions/flow-accumulation-with-weights/m-p/722603#M10482 <HTML><HEAD></HEAD><BODY><SPAN>I have a problem with Flow Accumulation.</SPAN><BR /><BR /><SPAN>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°.</SPAN><BR /><BR /><SPAN>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 In each pixel the amount withdrawn in that respective pixel is given. I now want to accumulate these withdrawals, becuase once I have withdrawn a certain amount in one cell, this amount is ging to miss in the downstream river as well.</SPAN><BR /><BR /><SPAN>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).</SPAN><BR /><BR /><SPAN>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? </SPAN><BR /><SPAN>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.</SPAN><BR /><BR /><SPAN>Does anyone know what I am doing wrong?</SPAN><BR /><SPAN>Thanks a lot!</SPAN></BODY></HTML> Wed, 27 Jun 2012 12:06:06 GMT FrancescaVerones 2012-06-27T12:06:06Z Flow accumulation with weights https://community.esri.com/t5/arcgis-spatial-analyst-questions/flow-accumulation-with-weights/m-p/722603#M10482 <HTML><HEAD></HEAD><BODY><SPAN>I have a problem with Flow Accumulation.</SPAN><BR /><BR /><SPAN>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°.</SPAN><BR /><BR /><SPAN>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 In each pixel the amount withdrawn in that respective pixel is given. I now want to accumulate these withdrawals, becuase once I have withdrawn a certain amount in one cell, this amount is ging to miss in the downstream river as well.</SPAN><BR /><BR /><SPAN>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).</SPAN><BR /><BR /><SPAN>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? </SPAN><BR /><SPAN>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.</SPAN><BR /><BR /><SPAN>Does anyone know what I am doing wrong?</SPAN><BR /><SPAN>Thanks a lot!</SPAN></BODY></HTML> Wed, 27 Jun 2012 12:06:06 GMT https://community.esri.com/t5/arcgis-spatial-analyst-questions/flow-accumulation-with-weights/m-p/722603#M10482 FrancescaVerones 2012-06-27T12:06:06Z Re: Flow accumulation with weights https://community.esri.com/t5/arcgis-spatial-analyst-questions/flow-accumulation-with-weights/m-p/722604#M10483 <HTML><HEAD></HEAD><BODY><SPAN>Maybe I'm getting you wrong here but note that the weights input into a flowaccumulation function multiplies the wt X flowacc in each cell.</SPAN><BR /><SPAN>So in this application your wt grid should be a proportion of water vol removed / total water, ie a number between 0 and 1.</SPAN><BR /><SPAN>Might need some extra toil here but if the water is extracted at only certain points then they should be set appropriately (like 0.75 meaning 25% of the input has been extracted) and all other values set to = 1 (100% passes through).</SPAN><BR /><BR /><SPAN>I think this should work.</SPAN><BR /><SPAN>Cheers, N</SPAN></BODY></HTML> Thu, 28 Jun 2012 14:18:55 GMT https://community.esri.com/t5/arcgis-spatial-analyst-questions/flow-accumulation-with-weights/m-p/722604#M10483 NeilAyres 2012-06-28T14:18:55Z