10 yr existing storm event greater than proposed

[Sathre]

I'm comparing 2, 10 & 100yr existing events to 2, 10, & 100yr proposed events for an infiltration basin design. I can't figure out why my rates work for the 2 & 100 events, but the 10yr existing is greater than the 100yr existing. I've never had this happen before. Does anyone have an idea of what might be going on? It's a small residential site - empty lot developing 1 single family home.

 

[psmart]

Impossible to say without seeing the model. Make sure you have resolved any warning messages, which generally mean the results are questionable. Also make sure the event parameters are correct.

Peter Smart
HydroCAD Software

http://www.hydrocad.net

 

[psmart]

Your title says "10 yr existing storm event greater than proposed", but your text says "10yr existing is greater than the 100yr existing".

Please clarify your question and post your HydroCAD file.


Peter Smart
HydroCAD Software

http://www.hydrocad.net

 

[Sathre]

Sorry, my 10yr existing rate is greater than the 10yr proposed rate. I'm not getting any warnings in the current model. I attached the model here. Its a pretty simple one.

 

[Sathre]

Sorry, model attached here

 

[psmart]

When you split the runoff area, and route one portion through a rain garden, it delays the peak flow so that the peak of the combined hydrographs is less than sum of the two peaks. You can demonstrate the effect if you bypass the rain garden and direct both subcats directly to the reach.

For details on offset peaks see

http://www.hydrocad.net/peakflow.htm

Peter Smart
HydroCAD Software

http://www.hydrocad.net