Wholly H2o - California's Integrated Water Reuse Management Center

Rain gardens suit this goal remarkably well. A rain garden is designed around a porous gravel or sand catch basin, infiltration basin or contour ditch called a "swale." The aim is to first capture rainwater runoff from impervious/impermeable urban areas like roofs, driveways and walkways, and then allow the water to infiltrate by way of a natural water filtration process using soil and plant roots.

The rain garden system has an added benefit of biologically filtering and sequestering pollutants, excess nutrients and toxins through the porous medium of gravel, sand or porous soils. Infiltrating rainwater into the soil on-site keeps polluted storm water from being carried offsite into storm drains, and prevents pollutants from entering streams, rivers, estuaries, and oceans.

When designing rain gardens, the following elements should be incorporated whenever possible:

Berms and Swales
These contoured earthworks contain and direct the flow of water. Simply stated, a berm is a linear narrow level space, shelf, or raised barrier of soil. A swale is a ditch with a level bottom dug along the contour of a slope.

Diversion Ditches (V Ditches)
These ditches are dug slightly off contour to move water slowly away from areas designated not be saturated to rain gardens where water can provide a benefit. Example: upslope from building foundations.

Compost
Utilizing compost assists soil composition, feeds plants, and reduces organic waste in landfills.

Mulch
Mulches are coverings made up of organic matter that prevent weed growth, add interest and color to landscape, and conserve soil moisture. Mulches should be directly placed on soil or breathable fabric in planting areas and never on plastic sheeting. Rain gardens are constructed by filling basins in low-lying areas with a porous soil blend, hearty plants, mulch and sometimes a gravel layer.

Native and Drought Tolerant Plants
Appropriate plant selection is key. Native, perennial, drought- tolerant, low-maintenance flowers and grasses provide color and tolerate local climatic conditions.