Catchment flow is zero even though correct storm is selected


Product(s):PondPack
Version(s):10.02.00.01
Area:Calculations

Problem

Catchments have zero flow (zero peak flow, hydrograph at a constant flow of zero) after creating and assigning a new storm event.

Solution

First, ensure that you are not just looking at the Flow at time zero. When a scenario is first computed, the results shown in the properties of elements will be from time zero and catchment flow would typically be zero before the storm begins. Right click on the catchment and choose Graph to see the hydrograph, or look at the peak flow value.

Next, check the area and loss method of your catchments. For example with the SCS Unit Hydrograph Method using the SCS loss method, ensure that the SCS CN values are reasonable, with a value of 99 representing impervious pavement and a value of ~30 representing a very porous surface. If the CN is very low with a very small area, it is possible that all of the runoff is soaking into the ground.

Next, ensure that the scenario you are looking at is using a rainfall runoff alternative with the correct storm event assigned. Go to Analysis > Alternative, expand Rainfall Runoff, double click the alternative with the red check mark (the one used by the current scenario), and check the Global Storm Event dropdown to ensure the correct storm is selected. Click the "..." button to review the storm event group and storms within it and their total depth values.

Next, check the properties of the catchments and ensure that the "Use Local rainfall" is set to False (so that it uses your global storm). Or, if you intended to use a local storm, ensure that the correct storm is selected in the catchment properties.

If you have confirm that the scenario in question is using a rainfall runoff alternative whose assigned global storm event has non-zero depth values, you may have encountered known issue #560943 related to an internal corruption in the storm event. To fix this, try editing and re-saving the storm using these steps:

  1. Go to Components > Storm Events and click the name of your storm event group on the left
  2. On the right side click the name of the storm within the storm event group, then click the yellow Edit button
  3. Re-type the same total depth value that the storm was already using (and same Duration, for storms that were based upon a dimensionless Time distribution). Click OK, click Close
  4. Re-compute the scenario and the catchments will show flow above zero.