How to model ditch

[Jmeng1026]

I am trying to determine how big (depth and width) a roadside ditch needs to be to act as a detention basin. Do I use a reach or a pond for this? The ditch will be a consistent depth and width but it will follow the slope of the road so it will have a 2% slope.

 

[psmart]

A reach is used only for modeling conveyance by normal open-channel flow. If you want to model the reach as a detention basin then you will need to use a pond.

The easiest way to model storage in the sloped channel is to use the "Pipe Storage" option, with a shape that most closely approximates the ditch. For other shapes you will need to use "Custom Storage" and enter stage-area data based on a topo of the ditch.


Peter Smart
HydroCAD Software

http://www.hydrocad.net

 

[Jmeng1026]

I have used the custom storage before to model a detention basin that is basically a pond but if I use custom storage for a sloping ditch how do I account for the slope of the ditch. I can't say the elevation of the ditch is say 105.0 because it goes from 105.0 down to 103.0 (depends on slope and length of ditch but I just threw this number in).

 

[psmart]

Draw contour lines across the ditch and enter the surface area at each contour, just as you would for a graded pond.

Or use the Pipe Storage option, which can be sloped.

Peter Smart
HydroCAD Software

http://www.hydrocad.net