Iniltration chamber bed outflow 1

[willcoll100]

I have modeled a roof runoff infiltration chamber bed in HydroCad, which had a primary
(6" pvc) outflow of 0.25 cfs for a 25 yr. event, and a 0.36 cfs for the 100 yr.
The 25 yr. total for the site was 0.03 cfs higher than pre development and the
reviewing engineer wants it the same or less to meet the town's stormwater management requirements. To be safe I added another row of 3 chambers which reduced the 25 yr.
outflow to0.07 cfs, but the 100 yr outflow increased to0.47 cfs putting that over the
pre development flow. All rainfall and other pertinent data other than storage remained
the same.
Is it right or does it have something to do with head? I doesn't seem that adding storage
volume should reduce 1 outflow so much while increasing the other.

willcoll100

 

[psmart]

Are there any warning messages? If so, they must be resolved in order to obtain meaningful results.

If the storage is overfilled, then you need to include appropriate overflow information as discussed at

http://www.hydrocad.net/chambers/overflow.htm

Otherwise, it's difficult to comment without seeing the HydroCAD project file. The placement of outlet devices can have unexpected results.


Peter Smart
HydroCAD Software

http://www.hydrocad.net