Problem Designing Stormwater Management Adjacent to Existing Brook 1

[StormMaster]

Hi All,

I am presently working on a project that involves the construction of 4 new residential buildings adjacent to an existing residential building, on a 0.65 acre parcel. Stormwater runoff from this site in both pre- and post-development conditions drains towards an existing brook located, on average, approximately 50 ft. from the rear of the proposed buildings. That said, the seasonal high groundwater surface elevation is very close to the surface of the ground, so infiltration would be minimal.

I would like some ideas as to how I can address stormwater management on this site. I was thinking about utilizing a vegetated swale with check dams, not for infiltration purposes, but to slow down the volume and flow of runoff tributary to the brook from the site.

I am open to any other ideas that you guys/girls may have.

Thanks...

 

[dicksewerrat]

you have the right idea. Extend the vegatative swale downstream to give the water more time to slow down and deposit the fines. this will also give the plants some time to absorb some of the lawn fertilizers.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[harringr]

You have not defined the problem ... if you are trying to control quantity or quality of discharge. If it is quality the Maryland SWM Design Manual has a whole chapter on nonstructural devices you can use (credits). There are also some low impact development techniques such as rain gardens. Prince Georges County has a very good ESD (Environmental Site Design Manual). You should find an acceptable solution there.

Vegetated swale with check dams are undesirable in the rear of yards ... expect a boatload of complaints about standing water, mosquitos and west nile virus. A rain garden with nice planting would also have standing water but would be more aesthically acceptable.

If it's quantity that is an issue - good luck. BTW if it is within 50 ft of a stream consider a floodplain study so you don't end up with flooded houses.

 

[sammyk]

Im with Harring. Do you need Detention? Or are you trying to acheive a reduction in soil erosion?
Some other things to consider:
Is there floodplain encroachment from the Brook
Are there proposed basements?
A vegetative swale with check dams will not provide you with detention. A proper shallow detention facility is what it sounds like you need. Try using a retaining wall and dig out the rear yard with a positive outfall to Normal Water Level.
That way even with floodplain you wont have to provide comp storage.

 

[blueoak]

I like the idea of a little created channel system. Dig a few deep areas where groundwater will help form longer duration pools, put in some drop structures using large diameter stones as a waterfall effect. You can claim a multitude of credits for detention, bio-removal, and any new hot words being thrown around. Also this will let you define the path for something up to a 10yr event and armor an entrance (I mean armor in a bio-sensitive swale/berm way). With backyards against a creek it is this uncontrolled overflow that can really chew up a nice stretch quickly.

 

[civilperson]

A granular dike between the runoff detention and the stream will allow seepage into the stream. Adjust speed by gradation.

 

[tsgrue]

.

Normally I wouldn't recommend such as these are systems which require regular maintenance (or inspection at least), but this sounds like a situation that may be partially addressed with cisterns (above ground). You may be familiar with these already (images at "

http://www.lid-stormwater.net/raincist/raincist_home.htm").

Cisterns could handle all the roof drainage and then either filter out slowly (maybe to supply a trickling bird bath), be used for wash water, or something else. Make sure the tanks are opaque to retard algae growth. As you have a high soil water table, the above ground type facilitates drainage out of the container without the need for pumps.

The parking lot and other hardscape stormwater runoff is tough given the high soil water table and proximity of stream channel. (The prior flooding comment also seems appropriate). I focus on infiltration for stormwater management. You could try a long and narrow berm/bioretention/infiltration area along the back of the lot (between the buildings and the stream). This depends on site relief/topography, but you might be able to implement one of these that would focus on lateral (horizontal) seepage flow through the berm to the stream channel as opposed to vertical (downward) flow. (For those unfamiliar with this in general, see images at "

http://Britannica/be/art-3242/Paths-of-seepage-through-embankment-dams",

“

http://www.duluthstreams.org/stormwater/toolkit/images/berm.gif”

and “

http://edis.ifas.ufl.edu/images/1285397791”).

I have done this before and have 3 on a current project on the edge of a perennial stream. These work well if you have the relief. (With tight/clayey soils, you may have to build the berm from sandier imported material or build the core with rip-rap overlain with a geotextile - the latter not prefered). These lateral seepage systems can double as a sediment basin/pool/trap during construction (just be sure to scrape out the fines and scarify well when converting from the temporary erosion/sediment control measure to the permanent stormwater management measure). You can achieve very good retention and detention performance with these (if designed and built appropriately - and you have the proper site conditions). This could also double as a nice landscaped area. Thick, evergreen vegetation works well, but you can use a turf grass as well and achieve good results. If you are not familiar with suitable plants/turf for your area, I suggest contacting your State extension service or the horticulture, forestry, and turfgrass academic program that serves your area.

I don't recommend permeable/pervious pavement for the vehicular areas or any areas which come into even moderate contact with greases, oils, or fines. These can have high failure rates when exposed to such constituents, even with relatively regular maintenance. Once the greases, oils, or fines get down into the pavement matrix, it is very tough to get it out (and expensive and time-consuming). Even a little coat can easily seal these. (You've probably seen the very little amount of clays it takes to clog a sediment pool). Permeable/pervious pavement also costs more to repair than standard pavements and that may be required for reasons other than the pavement failing (such as underground utilities or general landscape changes).

Let me know if you need any assistance/direction on the analysis for the infiltration system (including seepage or mounding).

You may have thought of all of this already, but I hope this helps!

.


tsgrue: site engineering, stormwater
management, landscape design, ecosystem
rehabilitation, mathematical simulation

http://hhwq.blogspot.com