Pond Pack modeling a 6 hour storm duration
Pond Pack modeling a 6 hour storm duration
(OP)
Does anyone have some guidance for using Pond Pack to model a 100 year 6 hour storm event? We're being forced to compare a 100 year 24hr and a 100 year 6 hour storm event to determine which one produces a higher peak value. My intuition would have me believe its the 6 hour duration, but I'm having a difficult time setting this up in Pond Pack to validate my thinking. This is for designing drainage ditches along the perimeter of a Valley Fill in Western VA. Any thoughts? Thanks in advance.





RE: Pond Pack modeling a 6 hour storm duration
Robert Billings
www.newrivereng.com
RE: Pond Pack modeling a 6 hour storm duration
Although the peak rainfall intensity will be the same, the 24-hour peak runoff will be greater because of the larger overall rainfall depth and the non-linear nature of the SCS runoff equation. This causes the initial abstraction to be satisfied earlier in the 24-hour storm, so the peak rainfall intensity will produce a larger peak runoff.
Peter Smart
HydroCAD Software
www.hydrocad.net
RE: Pond Pack modeling a 6 hour storm duration
RE: Pond Pack modeling a 6 hour storm duration
RE: Pond Pack modeling a 6 hour storm duration
Peter Smart
HydroCAD Software
www.hydrocad.net
RE: Pond Pack modeling a 6 hour storm duration
RE: Pond Pack modeling a 6 hour storm duration
"Although the peak rainfall intensity will be the same, the 24-hour peak runoff will be greater because of the larger overall rainfall depth and the non-linear nature of the SCS runoff equation. This causes the initial abstraction to be satisfied earlier in the 24-hour storm, so the peak rainfall intensity will produce a larger peak runoff."
Remember, these are "nested storms". The 24-hour storm contains the entire 6-hour storm nested at it's center, so the peak rainfall intensity will be the same. But the additional rainfall during the first 9 hours of the 24-hour storm causes an increase in the peak runoff.
Peter Smart
HydroCAD Software
www.hydrocad.net
RE: Pond Pack modeling a 6 hour storm duration
The last time I ran Pond Pack I imported a runoff hydrograph created from HEC-1. I did this for existing and proposed condition since it was an existing basin. Then I performed a comparison using excel.
RE: Pond Pack modeling a 6 hour storm duration
RE: Pond Pack modeling a 6 hour storm duration
RE: Pond Pack modeling a 6 hour storm duration
jleiben, what rainfall distribution are you using? Is it one of the SCS/NRCS distributions, or something else?
Peter Smart
HydroCAD Software
www.hydrocad.net