It's about volume. Even though you're preserving the peak flows of the pre-developed conditions, the resulting volume is actually greater. This increase in volume, post-construction, is known to erode downstream channels. Hope this helps.
Terry Stringer
Hydraulics & Hydrology Software...
Here is a profile of that same scenario I ran in Stormwater Studio. Of course there is flow exiting the pond but it illustrates how quickly energy losses can add up. The pipe exiting the pond is under HDS-5 Inlet Control.
Hope this helps.
Terry Stringer
Hydraulics & Hydrology Software...
Technically the approach velocity will have a reducing affect on the computed EGL at the upstream end of your culvert. In the real world, the approach velocity is almost always neglected in favor of conservatism. The computed EGL loss is based on V^2/2g. To take into account the approach...
BeeJ67 is correct. What you're seeing is simply the energy loss (entrance, exit and friction) between the Manhole and the Pond.
Terry Stringer
Better Hydraulics & Hydrology Software
http://www.HydrologyStudio.com
Sorry for the late reply but perhaps you can file this for future reviews where a storm sewer system outfalls into a detention pond. The way to model that is like this:
1. After the storm sewer analysis has been completed (assuming Rational method was used), note the total C x A value at the...
Hydrology Studio is currently developing an equal to Hydraflow Express (acquired by Autodesk in 2007). Express was a great simple tool that included culverts, open channels, hydrology, weirs & orifices. It's exactly what you're looking for. Stay tuned.
Terry Stringer
Better Hydraulics &...
As for oscillations, I agree with beej, they're occurring naturally and we shouldn't be over alarmed. After all, we're typically stuffing a large amount of water through an orifice or something similar and it's going to create an immediate backwater, regardless of the Time Interval used. We have...
