TR-55 hydrograph issue

[ncst8pe]

We've set up a model using the SWMM hydrograph method initially, but this method yields times of concentrations that seem to be too high. When we switch to TR-55 and the Kirpich TOC method, the subbasins generate runoff with a more realistic TOC, but none of the flow enters into the junctions, so routing is not performed. Any idea what the issue is?

[Chris Maeder]

Check the CN values that you have assigned. If the value is too low, then all of the rainfall can be captured as infiltration and nothing will be translated into runoff.

Also, when using EPA SWMM hydrology method, it is important that you properly define the "equivalent width" value that is defined for each subbasin. This has a big impact on the computed TOC.

If you continue to face problems with your model, you can send it to our technical support engineers.

[ncst8pe]

Thanks Chris. Some of our CNs are as high as 98, and every subbasin does produce some runoff. However, when looking at the junction that the subbasin drains too, there is 0 inflow to that junction. This is the case for every junction.

[Chris Maeder]

Check the computational and reporting time steps. They need to be multiples of each other or you will find that there will be problems in the results. However, if you want, forward the model to me and I can review it.