Rain Gardens, Bioretention, Bioswales, Hedgerows, and more
Effective landscape techniques that beautifully put plants to work for you
Bioretention Cells, Bioswales, and some Hedgerows are sometimes referred to as "Rain Gardens", because they are basically doing the same thing in different situations. For example, a "Bioswale" is basically a kind of rain garden where water is slowed and filtered, but much of the water is directed to another location.
Bioretention is a more complex rain garden with drainage systems and amended soils.
Hedgerows are not technically rain gardens but can be used to slow surface water as it heads down slope, as an edge to a Bioswale, or as check dam
Example of a yard before and after installation of a raingarden.
What is a rain garden?
A rain garden is a landscaped depression in the land, with specially design soil that collects rainwater from a roof, driveway or other impervious surfaces and allows it to soak into the ground.
Curb cut extension
Curb cut raingarden
Curb cut inlet
A Bioretention cell (strip or trench) is more complex rain garden with engineered drainage systems in a slightly recessed landscaped area constructed with a specialized soil mixture, an aggregate base, an underdrain, and site-appropriate plants.
A bioswale is a slightly recessed landscaped area constructed downstream of a runoff source. At the beginning of a rain event, a bioswale absorbs and filters water runoff. Once the soil-plant mixture below the channel becomes saturated, the swale acts as a conveyance structure to a bioretention cell, wetland, or infiltration area.
There is a range of designs for these systems. Some swales are designed to filter pollutants and promote infiltration and others are designed with a geo-textile layer that stores the runoff for slow release into depressed open areas or an infiltration zone.
A Hedgerow, Filter strip, or vegetated buffer is a row of plants at the edge of an area, whose purpose is to slow surface water runoff, to assist in infiltration, and prevent soil erosion.
Using plants as a nonstructural LID technique can significantly reduce the impact of rainwater.
Vegetated areas provide a pervious surface for groundwater recharge, particularly during dormant or non-growing seasons. In addition, vegetation can remove pollutants from the runoff flowing through it.
The preservation of existing natural vegetated areas is a nonstructural LID-BMP that should be considered
throughout the design of a land development. Ideally, the more natural area to be preserved, the better.
Rain gardens are designed to be self-sufficient. Some weeding and watering will be needed in the first two years, and perhaps some thinning in later years as the plants mature, but a well-planned raingarden can be maintained with little effort after the plants are established.
Rain gardens function only as well as they are designed. Planning is needed as well as knowledge of soil and local weather conditions. Take the time to plan effectively.
Note: Don’t locate a rain garden within 10 feet of a building foundation, near the edge of a steep slope or bluff, in low spots that do not drain well, where groundwater is within one foot of the bottom of the finished rain garden, over a septic drain field or tank, over shallow utilities (call before you dig), or in areas that would require disturbing healthy native soils and vegetation. For more in depth information, see the online books below.