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Storage above asymmetrical weir

Storage above asymmetrical weir

Storage above asymmetrical weir


I've got a swale modeled to a pond node. In reality the pond node is a Riprap area that provides some storage. The riprap discharges water through an asymmetrical weir (which is the warped edge of the rirap due to the cross slope in that area.. When modeling the real world available storage in the pond node, I got an error stating it could not perform the calculation due to there not being enough storage. Because there is no "real" available storage downstream of the riprap being that it is on a slope, I added 0.1-feet to my highest elevation in the elevation column and input 1,000,000 sf as the surface area to represent a free outfall situation. Running the model I got no errors, but the water surface elevation above the weir was within the area of fictitious storage. Is this an acceptable way to model stone storage riprap on a slope?

Thank you!

RE: Storage above asymmetrical weir

Modeling as a pond would apply only if you have an outlet control structure that creates level-pool storage. Otherwise use a reach.

If you should decide to model this as a pond, make sure you define the storage to the top of the channel upstream of the outlet. This volume provides real temporary storage. It is not fictitious. Do not include any volume below the outlet since it is not part of the "pond". For details see www.hydrocad.net/overfilled.htm

Peter Smart
HydroCAD Software

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