Ran model with a couple of scenarios. considered project area isolated . Baseline retention and runoff volume total 165,000+m^3/yr for the parcel with grass/shrub landcover. Virtually all retained volume
Scenario one includes a fair amount of urban hardscape for the project polygon. Total retention volume and total runoff volume now total ~300m^3/yr. How can the magnitude of the results vary so markedly for the two scenarios. Is this possible? Where has the rest of the water volume disappeared to?
Thanks for posting and welcome to the forums. Could you help clarify the two different scenarios you are running and the results you are seeing? It sounds like:
Scenario 1
grass / shrub landcover
retention and runoff volume of 165,000+m^3/yr
Scenario 2
grass / shrub converted to a fair amount of urban development