I have a pretty good handle on most typical situations using the software, but have two more complex situations arising. Can anyone tell me how I can effectively model the following situations:
Situation 1.
I have overland flow paths that lead to a detention basin intended to be used for first flush quality improvement. Located in this basin is a manhole with a frame and grate 6" above the basin floor. As the basin fills up, it is intended that the excess flow be relieved by the frame and grate. However, due to upstream pipe connections to the manhole and the downstream system being undersized, I actually end up with surcharge through the manhole in larger events. MY SOLUTION: I added a detention basin and routed the overland flows flows to the basin. I connected the basin to the manhole using a orifice (bottom) and set the crest elevation appropriately. For the manhole I allowed surcharge and set the ponding area to match the footprint of the basin. MY QUESTION: The top water elevations for the basin and manhole don't match of course. How should the model be set up so that the levels interact with each other?
Situation 2.
From above, lets say, my basin can't handle the surcharge volume and I want excess flow above a certain elevation to flow out of the basin and into an earthern channel. MY SOLUTION: I converted my manhole to a diverter with weir diversion to the earthern channel. MY QUESTION: Again because the basin (with orrifice to diverter) and diverter (needs to divert flow from basin with its own weir) are two seperate elements, I am not sure that the model is accurate.
I know that this is long winded and confusing but, if anyone has any thoughts, please let me know.
Regards
Jesse
Note that I have reviewed your question. I believe that the way you have the model setup is correct for the first part. You can have the detention pond connected to a junction using an orifice (or pipe) and model the interconnection through the storm drain that you have at the bottom of the detention pond. Alternatively, you can have a small detention pond replace the junction. In that way, you can more accurately represent the storage area associated with the storm drain.
Note, however, that you will want to run your model using the hydrodynamic routing method. As such, you do not want to use a flow diversion structure, since it will be converted to a junction when operating the hydrodynamic routing method. However, to model the overflow, simply connect the weir structure to the appropriate storage element. (This is were it got a little confusing in your description.) If the overflow is from the detention pond, then connect the weir to this element. If the overflow is from the storm drain junction box, then connect the weir to this element.
If you continue to have questions, please provide me with a sketch of what you are trying to represent and your StormNET model file.
SITUATION1: Based upon the attached info, do you think that I am adequately modeling for the backwater effect from the overloaded stormdrain? (Note, I rely on the volume calculation of excess water out of the junction, not elevation because ponding in my parking lot is irregularly shaped)
SITUATION2: Basically, instead of letting water back into the parking lot, if I wanted to divert excess backwater above a certain elevation via overland flow path, where could I fit a diverter into this scheme?
I reviewed your PDF diagram and StormNET model file. The model appears to be handling the setup as you described.
The only concern I have about your model is that you are using the Rational Method for your runoff computations, and this method is really inadequate to check the detention pond size since it does not include the storm duration in its computations. I recommend either switching to the Modified Rational Method or one of the other event-based hydrology methods (i.e., TR-55, TR-20, EPA SWMM, HEC-1, etc.).
Linear Mode
