Low Impact Development Why is LID Important

Traditionally, storm water management has involved the to the environment?

rapid conveyance of water via storm sewers to surface
waters. Low Impact Development (LID) is a different
• protects sensitive areas
• increases habitat for wildlife by preserving trees and
United States
Department of
Agriculture
Bioswales
approach that retains and promotes rainfall infiltration on- vegetation
Natural
site. The LID approach emphasizes site design and planning • protects local and regional water quality by reducing
sediment and nutrient loads
Resources ... absorb and transport large runoff events
techniques that mimic the natural infiltration-based, Conservation
• reduces streambank and channel erosion by reducing Service
groundwater-driven hydrology of our historic landscape. What are Bioswales? Existing swales can be enhanced with
Bioswales are one component of LID. the frequent surges/bounces of higher flows from storm Montana native plants. The thicker and heavier the
sewer discharges 2007 Bioswales are storm water runoff conveyance
grasses, the better the swale can filter out
• stabilizes stream flow by reducing variability of surface systems that provide an alternative to storm
runoff; restores ground water discharges into receiving contaminants. Additionally, subgrade
sewers. They can absorb low flows or carry
surface waters drains and amended soils may be needed to
runoff from heavy rains and snowmelt to
• reduces potential for flooding facilitate infiltration.
storm sewer inlets or directly to surface
to residents? waters. Bioswales improve water quality by Other considerations when designing or
• increases community character enhancing infiltration of the first flush of maintaining bioswales:
• improves quality of life storm water runoff and filtering the large
• Costs vary greatly depending on size, plant
• increases open space storm flows they convey. material, and site considerations. Bioswales
• pedestrian friendly are generally less expensive when used in
About 30 to 40 percent of Montana’s annual place of underground piping.
to developers? precipitation comes from small rain events.
• Deep-rooted native plants are preferred
• reduces land clearing and grading costs Much of the value of bioswales comes from to promote water infiltration and reduce
filtering nearly all of this water. maintenance. They are also better at
• reduces infrastructure costs (streets, curbs, gutters,
controlling erosion.
sidewalks) Designing a Bioswale • Evaluate site soil conditions. Soil
• increases community marketability
For best results, enhance and utilize existing infiltration rates should be greater than
to communities? natural drainage swales whenever possible. one-half inch per hour.
• balances growth needs with environmental protection Maintain riparian areas before and during • Avoid soil compaction during installation.
• reduces infrastructure and utility maintenance costs construction to act as “natural” bioswales. • A parabolic or trapezoidal shape is
A road ditch can serve as a bioswale. The rock trench and wetland recommended with side slopes no steeper
vegetation are notable features along with the natural drainageway than 3:1.
in the background that serves as a bioswale for residential runoff. For More Information
• Collaborative projects with neighbors and
Find more information about low impact development and adjacent property owners are usually more
bioswales by visiting the following websites: effective at reducing runoff.
• Swales should be sized to convey at least
www.lid-stormwater.net
a 10-year storm (or about 2.4 inches in 24
www.cwp.org hours).
www.nrdc.org/buildinggreen/links/site.asp
Maintaining a Bioswale
www.plant-materials.nrcs.usda.gov/technical/
Once established, bioswales require less
publications/wetland.html
maintenance than turf grass because they
http://www.mt.nrcs.usda.gov/technical/ecs/water/setbacks/
need less water and no fertilizer. Native
More information on this topic is also available from your grasses and forbs are adapted to Montana’s
local NRCS or county conservation district office. climate and soil conditions. Native plants
also resist local pests, disease, and weed
The U.S. Department of Agriculture (USDA) prohibits discrimination in all its programs and activities on the basis of race, color, national origin, age, disability, and where applicable, sex, marital
status, familial status, parental status, religion, sexual orientation, genetic information, political beliefs, reprisal, or because all or a part of an individual's income is derived from any public assistance
This bioswale is planted with native sweetgrass (Hierochloe odorata.) infestations.
program. (Not all prohibited bases apply to all programs.) Persons with disabilities who require alternative means for communication of program information (Braille, large print, audiotape, etc.)
should contact USDA's TARGET Center at (202) 720-2600 (voice and TDD). To file a complaint of discrimination write to USDA, Director, Office of Civil Rights, 1400 Independence Avenue, S.W.,
Washington, D.C. 20250-9410 or call (800) 795-3272 (voice) or (202) 720-6382 (TDD). USDA is an equal opportunity provider and employer.

Bioswales Helping People Help the Land Bioswales

06/07/MT
 Bioswale in a Corporate Setting

Adapted from original illustration by Doug Adamson

Native Landscaping
Deep-rooted native shrubs, forbs, and grasses Strong Deep Roots
build soil structure and allow water to infiltrate
into the ground more easily than nonnatives. Native plants have a tremendous root architecture that
Native plants are low maintenance, adapted builds soil quality and increases organic matter content.
to Montana climate and rainfall patterns, and High organic matter content helps soil hold water like a
resist local pests and disease. sponge making it available for nourishing plants.

Infiltration
Soil Amending Water infiltrated through bioswales helps
Along with native plantings, soils amended recharge groundwater, which supplies rivers
with compost and sand may be needed to and streams with a slow, purified seep rather
facilitate infiltration. A rock trench can be than surges of polluted surface runoff from
installed down the center of the swale. roofs and other impervious areas.

Helping People Help the Land