Outlet protection for 6" pipe

[drhenne]

I am designing a storm water detention system which utilizes a horizontally run 6" PVC pipe as the primary outfall structure. Since the discharge is onto lawn, I need some type of difuser or splash guard at the outlet. Stone riprap is not desireable in this residential application. Can anyone offer a suggestion?

 

[mikolay]

You might consider capping the end of the pipe or providing a cap with a hole in it for reduced outflow with the additional provision of using perforated pipe for the last couple of lengths so that the area of the total openings exceeds the area of the single 6-inch opening with a F.S. Then the outflow won't be concentrated at the outlet end. From there the water needs to get away on a almost level surface so it doesn't tend to channelize again into a singular flow. You will probably need some type of erosion mat to hold the soils and vegetation in place in the flow path. The erosion mats have various life capabilities, allowing for biodegradation, etc. if that is the long-term goal.

 

[waterguy]

Something that I have used in the past was the idea of an "up-welling" outlet. Basically (in your case), you might consider having the 6" horizontal pipe buried, and at the very end you would install a vertical bend (pipe with elbow or small manhole type device ??). It might work depending on the elevations involoved and weather you have enough head driving the system. Outflowing water will spillout more gently rather then at a concentrated flow. This configuration will raise other issues with respect to the hydraulics involoved and the potential for increase backwater affects. I have used it in the past where a manhole structure was actually used as the "up-welling" structure to provide a more gentle introduction of pond outflow to a nearby creek. I've included a very crude sketch below.

[tt] flow wells-up from vertical riser
________________________
| * * |
| * ^ * |
| * | * |
*********** | * |
pipe * |
**************** |
| |
| clear stone trench
|_______________|
[/tt]