Stormwater Ditch modeling

[JTugwell]

Hello,

I am currently designing a stormwater retention system for a 257 acre surface mining area. I have to provide adequate capacity to contain a 25 year event (8.5 inches in 24 hours). I have the ability to construct a drainage ditch around the perimeter of the mining area which would route drainage to an area that has been previously mined. This ditch will be approximaely 8500 feet long, and I am concerned that I am not modeling it correctly.

What I have done in the past is break the mining area up in to smaller watersheds by looking at the topographic data and creating a subcatchment for each. I will then have the catchment report to a reach. Each reach will then input into the next successive reach until I have the entire watershed accounted for. I am attempting to model a ditch that is receiving input along its entire length. I am sure there is a better way to do this and was hoping someone could help me out here. I have read something in the user manual about including the ditch as a channel flow segment in the subcatchment modeling, but I don't understand how that works. Any assistance will be greatly appreciated.

-Jonathan

 

[psmart]

Since you are feeding the channel at multiple points, you will need to use multiple reach segments, exactly as you have done. Modeling the reach as a flow segment within a subcatchment would only apply if the reach were contained within a single subcatchment.

For further details please see

http://www.hydrocad.net/reach.htm

Peter Smart
HydroCAD Software

http://www.hydrocad.net

 

[JTugwell]

Would there be any benefit to modeling the entire 257 acre area as one subcatchment, and then including the ditch as a flow segment within? Or would I find more accurate results using the method described previously?

 

[psmart]

Your approach (multiple reaches and subcats) is probably more accurate. I would try it both ways and compare the results.

Peter Smart
HydroCAD Software

http://www.hydrocad.net