HydroCAD - Detention Basin Model

[ptr]

We are working on a project with a wet basin and a detention basin. They are not connected and are at different design points.

With the wet pond model, I have the permanent pool area as impervious area. If the detention basin drains dry, do I model the bottom area of the basin also as impervious?

 

[civilperson]

It will be after twenty years of silt settlement.

 

[psmart]

ptr - Sorry, your question is unclear. Are you modeling exfiltration from the pond? If so, you probably want to set the exfiltration "invert" to the permanent pool elevation, in order to prevent gradual draw-down. Presumbly you will also set the starting elevation to the same value.



Peter Smart
HydroCAD Software

http://www.hydrocad.net

 

[psmart]

A reminder: Please use the HydroCAD forum for questions that are specific to HydroCAD.
Forum789


Peter Smart
HydroCAD Software

http://www.hydrocad.net

 

[TerryScan]

ptr-

If I am understanding the question correctly, this is really a question of CN value and is not Hydrocad specific.

I understand you saying that you have a wet pond and a "dry" pond within the same watershed. You already plan to model the wet pond as an impervious surface and are unsure how to model the dry pond.

In dry weather, it is possible for the "dry" pond to drain completely. However, when you are running a hydrologic model, it isn't exactly dry weather is it? I think it would be safest to assume the basin is impervious even if you may be discounting some soil storage capacity at the beginning of the event (prior to runoff).

If you are actually modeling the "dry" basin as infiltration, it should stil be modeled as impervious in runoff calculations, since you don't want to "double count" the soil storage in the runoff componant and the routing component of modeling.

 

[ptr]

Thanks TerryScan

Yes..I guess my question was more of a CN value question.

We are not taking credit for infiltration, as the dry basin is for attenuation of peak flows only. I will treat the dry basin bottom as impervious for my model.