View Full Version : Sub-catchment Overlap

July 22, 2015, 10:43 AM

I have to work with an existing 1D sewer model, and I have noticed that several sub-catchments overlap. The overlapping sub-catchments are of storm and combined system type, so I was wondering if that makes a simulation account for rainfall twice. When I make a graph of runoff in the simulation output both (storm and combined) have a similar hydrograph. Each sub-catchment drains to a different node but the ones I am interested in result to the same outfall later on (which when compared to some observations I have, seem highly overestimated).

How can I make sure that rainfall is not added twice?

Thank you

August 10, 2015, 09:43 AM
When you say overlapping, are they partially or completely overlapping?
I would think that the most likely explanation is that it's a partially separate system, check in the subcatchment properties what the areas are and how these relate to the area of the subcatchment polygon. If it is a partially separate system, the subcatchment polygons have probably been drawn to indicate the maximum extent of the area partially drained by each system type, but the runoff areas input to for each type should be just what is drained by that type and hence the rainfall runoff isn't being doubly accounted for.
Hope this helps / makes sense!