Question
My backyard has a low area that repeatedly floods. Researching for solutions all suggest drainage tubing, berms, swells, ditches, etc. Due to the small size of my yard,the proximity of my neighbors, and the main fact that all of the surrounding area is uphill from the low area, these are not workable. I've looked at dry well kits sold at local home stores, but I don't think they would be able to handle the amount of water I get.
Any suggestions?

Answer
Hello,

The plastic drywells from the kits can be placed together in battery form. It would be a matter of determining the volume of water involved and placing the required number of drywells accordingly. You would have to excavate an area approximately 4 to 6 feet deep to place the drywells. A more shallow excavation containing permeable material such as gravel or rocks or sections of sealed large diameter corrugated drain pipe could also be a possibility but this would have to spread over a wider area than drywells. Any retention area containing gravel or rocks or any permeable material reduces the volume of water that can be contained because the material takes up space in the area. Drywells and drain pipe contain only empty space and so can hold more water. The drywells you saw at your local home store may be smaller than drywells available elsewhere.

Another possibility could be to install a cistern. This could be constructed of concrete or masonry. This method would prevent water from saturating the surrounding soil and would also aid in maintenance as it would be easier to service in the way of cleaning than a filled retention basin. Over time a filled retention basin will fill with silt and the materials must be replaced. The water could slowly leak out through a hole in the bottom or sides. An overflow pipe would relieve any excess water. This method would also allow you to use the water for your garden or some other purpose. Water could enter the cistern from a top drain inlet,screened to exclude debri. Covered with a layer of soil of about 18 inches,this method would allow you to use the ground above and would offer more storage volume than a filled retention basin. Prefabricated plastic cisterns are available.

I would also suggest a retention basin,which is sometimes also called a rain garden or bioretention basin. It could simply be an area of permeable soil or some type of "engineered soil" placed in various layers to achieve the greatest degree of drainage possible. With a rain garden you will have to accept a certain amount of water for up to 48 hours and this will restrict your use of the area but if you want to use the area for planting,then you could fill the area with plants that thrive in rain gardens. These plants could also include certain edible types. The soil surrounding the retention basin must be permeable enough to allow the water to drain sufficiently.

An outlet for some of the water may be desirable. You may want to try to get permission from your municipality to connect to the storm drain. Most often the connection must be done by a licensed plumber. It may also be possible to discharge some of the water off site,say onto a low traffic road but there must be no possibility of water standing on the road. This water could cause a traffic hazard and can freeze in winter.

The lifespan of these structures can be extended by using some type of device to trap sediment before it reaches the structure. These sediment traps require periodic cleaning. Good luck. Let me know if I can be of further help.

Mark Harshman
http://www.mahdrafting.com
Email: [email protected]

http://www.allexperts.com/ep/724-104627/Landscaping-Design/Mark.htm