Foundation drain with concrete curb prior to rock or mulch.

Foundation or perimeter drains are often installed as landscaping around homes built on grade such as found in Florida. This BMP would not be suitable for locations with basements in that they are typically adjacent to the foundations. This technique utilizes a curbing system of some type with varying widths and is usually filled with gravel or landscape mulch. It is also common to install plants as part of the landscape plan, locally friendly plants are recomended.

For this BMP, a total depth of 4” is used and 2” of the depth is placed in rock or mulch. Porosity for the rock layer is default to 35% (default) and for mulch is 40% (Physical Properties of Woodchip: Compost Mixtures; C.S. Ima and D.D. Mann) (change the porosity under the "show advanced options" to 40% if using mulch). Both installations allow for the top 2” to allow full volume storage prior to overflow as well as includes a drain tile that can also discharge the water collected. If the drain tile discharges under the curb it should be routed to another BMP to allow a “treatment train” for the runoff.

For rock lined foundation drains it is recommended to place a filter fabric at the bottom of system to separate the soil from the rock to minimize clogging and allow free flow into the ground. For foundation drains that use woodchips it is recommended to rototill or mix the chips into the existing soil and then add the 2” of mulch on top of the amendment. The depth of the soil mixture also allows additional storage of rainfall and porosity based on the Ima and Mann study indicates 40% for porosity.