Vegetated bioswale channel with native plants and boulders at the UGA GSI demo site

Stop 6: Bioswale

Overview

A bioswale is a vegetated, gently sloped channel designed to convey, filter, and infiltrate stormwater runoff. Planted with native and adapted species and lined with stone, bioswales slow water velocity, filter pollutants, and allow infiltration as water moves through the landscape—combining conveyance with treatment.
Practice Type: Vegetated conveyance and filtration channel

Quick Facts

DimensionsApproximately 15 ft. long x 6 ft. wide
Channel SlopeLess than 2% downstream
FeaturesNative plants, 18-inch boulders, medium flat river rock
Cost Range$5 to $25+ per square foot (materials and labor)

The Problem

When stormwater flows across developed landscapes, it picks up pollutants—sediment, fertilizers, pesticides, oils, and other contaminants—and carries them directly to streams, rivers, and lakes. Fast-moving runoff also causes erosion along its flow path, damaging landscapes and infrastructure.

The Solution

Bioswales transform drainage channels from simple conveyance systems into living water-treatment features. By combining gentle slopes, native vegetation, highly permeable soil mixes, and strategically placed stone, bioswales slow water velocity (allowing sediment to settle), filter pollutants through plant roots and soil, and promote infiltration into the ground.

How It Works

At the demonstration site, the bioswale receives water flowing from the existing dry creek bed, downstream of the foot bridge. As water moves through the channel, plants and boulders slow its velocity and spread the flow across the swale width. The slowed water has time to infiltrate into the soil, reducing the volume of stormwater reaching the rain garden downstream.

Design Specifications

Key Specifications

  • Channel length approximately 15 feet, width approximately 6 feet
  • Maximum downstream slope of 2% (no more than 4 in. drop from beginning to end)
  • Maximum side slopes of 2:1
  • 18-inch boulders placed to slow and spread water flow
  • Medium flat river rock for channel bed stabilization
  • Native and adapted plant species for filtration

Water flow: Receives water from the dry creek bed and directs flow to the rain garden (Stop 7).

Try It Yourself

Bioswales can be adapted for residential properties wherever water naturally flows across the landscape. Even a small swale along a property line or between a driveway and lawn can significantly reduce runoff velocity and filter pollutants. Home-scale bioswales are typically narrower (3-4 feet wide) and can be designed as attractive garden features using native perennials and ornamental grasses.

For Professionals

Bioswale design for compliance applications should reference the Georgia Stormwater Management Manual for sizing calculations, vegetation specifications, and maintenance requirements. For larger commercial projects, bioswales are often integrated into site drainage plans as a pre-treatment measure before water enters detention or retention systems.

Resources

Download fact sheets, design guides, and technical resources for this practice.