Modeling 10 day snow melt

[Sathre]

Anyone know how to correctly model the 10-day 100-yr snow melt with HydroCAD?
I have set up my model with storm type as the Spillway 1-day 10 day, duration for 240 hrs, and adjusted my AMC to be 4 (using Atlas 14 rainfall). This still indicates that I would be getting infiltration out of my basin though. Does anyone know if this model is correct? Maybe all I just need to manual remove the exfiltration outlet every time I run the model.

Thanks

 

[psmart]

AMC 4 is a special HydroCAD setting that increases all CN values to 98, and can be used to model runoff from frozen or impervious surfaces. However, it only models RUNOFF and not water from snow melt.

You can use this option with any rainfall distribution you choose, such as a Type II 24-hour. But the spillway distribution really isn't intended for this purpose.

It would help to know the purpose of your calculations. Perhaps others have dealt with a similar situation.


Peter Smart
HydroCAD Software

http://www.hydrocad.net

 

[Sathre]

As part of the watershed review I need to model 10-day, 100-yr snow melt as my critical event for ponds in a residential site development with B type soils. I used the spillway distribution as I had done some internet searching and that was the direction I was finding. Even if I switch it back to the type II storm I am still coming up with High Waters for my snow melt that are less than the 100-yr storm event. In speaking with the watershed they don't think that would be accurate so I am looking for a better model.

 

[psmart]

My experience is that snow-melt calculations are rarely done, partly because the 100-year event produces greater runoff, so a separate snow-melt calculation is not required. Of course, if an agency is requiring a snow-melt calculation, you will need to to do the calcs in the manner they require.

Peter Smart
HydroCAD Software

http://www.hydrocad.net

 

[Sathre]

Thanks. The watershed/ City argue that the snow melt will be the critical event. Is there a way to turn off the exfiltration in storm event without erasing it from my basin/pond?

 

[psmart]

You can disable any outlet device (such as exfiltration) by setting it's discharge multiplier to zero.

Peter Smart
HydroCAD Software

http://www.hydrocad.net