H&H Study Question

[Engdawg]

I have a project where I am analyzing a neighborhood for a 100 yr storm event. The current design drains each street into a canal. When the canal rises above the outfall culverts, valves close and the ditches are alowed to backwater until they spill over into a ditch on the far upstream end of the ditches. This ditch then drains into a retention pond where it is pumped into the canal. The site is flat and the current ditches are at slopes of 0.25% to flat.

I need to model the above scenario, but can not come up with a reasonable means of analysis. I need to take advantage of the flow that gravity drains into the canal because the sit can not drain a 100 yr flow into the pond without flooding (which is one reason for the study). I know improvements have to be made, but have to justify them via some means of analysis....

 

[TerryScan]

With a slope of 0.25% to flat...for modeling purposes of a 100 year event, I would call it flat. Model the culverts as storage with an outlet to the canal at a lower stage and the overflow at an upper stage.

 

[Engdawg]

TerryScan,
Thanks for the reply. Thats how I began modeling the project, but my issue is with modeling the valves so that the outflow into the canal stops once the canal is higher than the culvert (valve closed). I am using Hydrocad to do the modeling.

 

[gbam]

Engdawg - for future reference there is a seperate forum just for hydroCAD. From what I have read Peter ids the go to guy for that program.

As to your modeling question, since i am a bit old school I would create rating curves reflecting the stage storage and discharge which including the zero discharge for when the shutoff valve is off.

 

[psmart]

HydroCAD will do exactly what you want with the one-way flow. By default, the outlet devices only pass flow in one direction. If a reverse head situation occurs, you'll get a warning, but there is no flow through the device (unless you explicitly model a reverse flow, but that's another story.)

Peter Smart
HydroCAD Software

http://www.hydrocad.net

 

[TerryScan]

To supplement Peter's comments, be sure you are using Dynamic Storage-Indication as the calculation method. This will take into account tailwater effects on the pond routing (the plain storage-indication method does not). With this method, flow will go to zero when tailwater reaches the pond elevation.