Urban stormwater runoff results

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?

What do you expect to happen?

What have you tried so far?

Attach the logfile here:

Hi @glomnick,

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
  • retention and runoff volume of 300+m^3/yr

Are you looking at results in aggregate.gpkg?


Yes results are from the aggregate.gpkg.

Scenario 1: Baseline for entire site is grass/pasture with a bit of shrub.

Scenario 2: large portion converted to business park and gravel parking. About 80% of site. One portion converted to shrub scrub green area.