Ephemeral Stream as Stormwater management ?????
Ephemeral Stream as Stormwater management ?????
(OP)
I did a land development for a single family house. The area for the project is 1.72 ac approx. The runoff from the new development is about 50cfs. There is an ephemeral stream on the site which I thought could be used for drainage. So, I have graded my site such a way that all the water gets dumped on the stream by overland flow. I am trying not to have a structured BMP for this project coz the runoff generated is really small. Now, the problem is county wants me to show that it meets state and local Stormwater management requirement. I am wondering if any one of you has any idea about incorporating drainage on ephemeral stream through overland flow. This project is in Montgomery County, Maryland. Any suggestions will be highly appreciated.





RE: Ephemeral Stream as Stormwater management ?????
Thats probably your problem right there, the county guy hears 50 cfs, which is like the 100 year storm event for a 6 acre commercial development in Texas.
RE: Ephemeral Stream as Stormwater management ?????
RE: Ephemeral Stream as Stormwater management ?????
Common stormwater regulations require treatment of the peak runoff from the 2 yr storm.
Why are they designing the BMP to treat a hurricane?
RE: Ephemeral Stream as Stormwater management ?????
RE: Ephemeral Stream as Stormwater management ?????
I'm not familiar with the exact stormwater requirements for Maryland, but some pretty common ones are no increase in the peak runoff rates for the 2, 10, and 100 year storm events and BMP should be designed to treat the runoff from a 2yr storm or the volume of runoff from a 1 to 1.5 inch rainfall.
The rules vary by location, but it sounds like you'll need to do some basic hydrology calcs to show that the increased runoff from your site isn't affecting anything downstream.
RE: Ephemeral Stream as Stormwater management ?????
jgd2, maybe post a pdf of the county ordinance pertaining to this issue. I'd be curious to read it.
RE: Ephemeral Stream as Stormwater management ?????
RE: Ephemeral Stream as Stormwater management ?????
It really only says you need to convey additional water from new impervious areas away from adjacent properties so as not to adversely affect them.
In your case, I would indicate that you will utilize overland release (sheet flow/swale flow) across landscaped area into a natural drainage course. Then certify (if you can) that flows from the new impervious areas will not go to adjacent properties. (If some must go to the ROW, you'll need another permit per the odinance).
This allowance comes under the 'natural topography/buffer' on pp8. As long as the lot does not exceed 5% slope (does it?)
RE: Ephemeral Stream as Stormwater management ?????
RE: Ephemeral Stream as Stormwater management ?????