Wetland Berm Design

[PBW2]

I am in the process of designing a small berm to be located along the edge of existing wetlands at the back of private lots. Currently when the WWTP discharges into the basin (series of interconnected ponds/pipe/wetlands) the water encroaches onto the private property. The intent is to design the berm to keep the water out of the yards. However, the yard slope is from the road to the back of the lot (wetlands)so we also need to direct the storm water to the wetlands.

The challenge will be to design the berm to keep the water out of the backyard but also allow for drainage from the lots into the wetlands. To put it in perspective we are looking at a 2' high berm approximately 500 lf across the back of 4 lots. Any and all suggestions are welcome.

Thanks

 

[francesca]

I assume that the water level in the wetland is usually below the base of the berm and that you're trying to protect against storm/flood conditions.

If so, turn the back of your lots into a detention basin with a check valve on the outflow pipe. Actually I've seen devices as simple as a rubber sheath on the end of the pipe that opens in response to flow down the pipe but doesn't allow return flow. Well, I've seen them in catelogues, not actually in use, but presumably you'd be able to remove the rubber sheath pretty easily to flush the pipe if it gets blocked.

 

[DMcGrath]

The valves in the picture from francesca are called "Tide Flex" valves by the Red Valve Co. They look simple, but they are not by any means cheap (inexpensive). Remember that water needs a downward gradient to flow, and if the water level on the wetland side of the berm is higher than the lot side, you won't be able to get any water to flow out of the lots. Richmond (VA) has a wonderful flood wall to keep the James River from flooding downtown. Recent storm events have shown that the flood wall works both ways - keeps water out and keeps water in!

 

[blueoak]

I've used flapgates from waterman which are similar (only for ag and wetland projects, no homes). The one thing to remember is that maintenance is important. I have seen them plugged shut with sediment on the downstream side after large storms and the next storm couldn't open them. This was for a diversion from a creek to a wetland. I assume that after the water levels equalized the flap shut and then sediment on the wetland side settled.

Also I have seen trash holding them open so a screen is sometimes needed.

My friend's house is in a similar situation. They keep a pretty good sized pump in their garage. Is the wetland the natural drainage path or just a depression?