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Green Basics

Stormwater: Rain Gardens and Drywells

Temporary Water Storage Helps Recharge Aquifers and Reduce Water Pollution


Returning water to the earth gently

A rain garden is a depression in the ground that’s been filled with permeable materials and capped with plants such as wildflowers, shrubs, and small trees. Unlike roadside swales, rain gardens are intended to hold the runoff that enters rather than act as a pass-through.

Water disperses slowly through percolation and the transpiration of water back into the atmosphere through plant leaves. The process is called “biofiltration.”

A less expensive alternative

The rain garden is a relatively new concept in landscape design, but it is growing in popularity.

Rain gardens were originally developed in 1990 by a developer of a residential housing project in Maryland who was looking for an alternative to conventional retention ponds for runoff control. Each house in the subdivision was designed with a rain garden that covered between 300 square feet and 400 square feet. The approach was effective and cheaper.

Since then, rain gardens have been used in projects all over the country. In one Seattle demonstration, rain gardens incorporated into an overhaul of a residential street cut the amount of stormwater runoff by 98%.

Rain gardens mimic natural ecosystems

Residential development creates impervious surfaces that prevent runoff from dispersing slowly and percolating into the soil. Erosion, the pollution of lakes and streams, and more strain on municipal sewage plants and stormwater systems are three unfortunate results.

Rain gardens are a relatively simple but highly effective tool for managing runoff. They work in much the same way as an undisturbed ecosystem.

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