Primary Outlet Device--Culvert

divingunder · Jan 18, 2008

I am modeling a detention pond with a 12" culvert as my primary outlet (discharge pipe). After routing, my results show a discharge above the capacity of my pipe. I have a 12" ADS pipe with a .5% slope. Modeled discharge is 4.78cfs and the full discharge of that pipe is approx 2.5 cfs. I am not receiving an error message and I am wondering if any HW is being accounted for.

bpattengale · Jan 18, 2008

HydroCAD takes into account the HW when calculating the flow through the pipe. The 2.5 cfs is the capacity under gravity flow using mannings. Based on your description the culvert likely has a significant ammount of head on the pipe causing it to flow under pressure. If you want to double check the HydroCAD comps by hand recalculate the flow using the Darcy-Weisbach or Hazen Williams formula.

psmart · Jan 18, 2008

A culvert outlet on a pond always considers headwater and inlet conditions. Headwater can cause the flow to exceed the normal Manning's capacity of the pipe. On the other hand, high values for the entrance energy loss coefficient Ke can result in flows that are less than the Manning's capacity.

Peter Smart
HydroCAD Software

http://www.hydrocad.net

Tek-Tips is the largest IT community on the Internet today!

Members share and learn making Tek-Tips Forums the best source of peer-reviewed technical information on the Internet!

Primary Outlet Device--Culvert

divingunder

Civil/Environmental

bpattengale

Civil/Environmental

psmart

Active member

Similar threads

Part and Inventory Search

Sponsor