Using Low Impact Development to Enhance Communities

landscape architecture design low impact development

Bioswales capture a storm’s first flush, which contains most of the pollutants from paved surfaces.

It doesn’t rain very often in the desert, but when it does, we often lose the opportunity to capture an increasingly important resource: water. Stormwater provides a free source of irrigation water for landscapes and reduces the burden on city storm drainage systems. Where low impact development (LID) practices are used, naturally occurring storms can help conserve water use and reduce flooding hazards in urban areas. By capturing stormwater and using it close to its source, LID can enhance communities and reduce the impacts of development on downstream communities, streams and rivers.

LID was originally developed to reduce flows to combined sewers in coastal cities, and improve water quality at outfalls into natural water bodies. It is a landscape architecture design approach that can provide low tech, user friendly ways to apply water resource conservation at a local level. LID is now being adapted for use in arid areas of the Southwest where infrequent and unpredictable storms can wreak havoc in urban areas.

The cities of Mesa and Glendale, Arizona recently used a grant from the Water Infrastructure Finance Authority of Arizona to develop a LID Toolkit to educate and provide guidance for city agencies, businesses, and residents about more sustainable stormwater design and management practices.

The Toolkit identifies current and new stormwater best management practices and how they might be designed and integrated into a variety of contexts in the urban environment. It also identifies possible incentives that can be used by the cities to encourage LID use in both public and private development and redevelopment.

The Southwest’s population is still growing, and more people want to live in urban areas, where higher densities of buildings and more pavement increases the volume of stormwater runoff (and pollutants) during storms. Rapid runoff of rainwater from rooftops and paved surfaces causes potentially dangerous flash flooding downstream. LID tools are now available for landscape architects, planners, and engineers to use to help reduce stormwater impacts while improving landscapes and saving water.

The Southwest desert environment doesn’t support many plants in urbanized areas without the need for supplemental irrigation. As witnessed in California this year, drought and demand are straining existing water resources. When stormwater is directed into landscape areas instead of into runoff and storm drain systems, it can provide enough supplemental water to sustain a greater number and variety of native and non-native plants.

The natural quality of desert washes, streams, and rivers are diminished by development encroachment, creating inconsistent stream flows, increased peak runoff and impaired water quality. This reduces their ability to support riparian vegetation, wildlife habitat, and recreational use. Natural areas are highly valued in the Southwest for their visual beauty, diverse wildlife, and access to open space and recreational trails. Integrating natural open space into urban environments increases both livability and property values.

Urban areas also tend to be much warmer than they were before development. This is caused by pavement and buildings that absorb the heat and release it at night, and cooling systems that generate outdoor heat to cool building indoors. Shade created by enhanced landscaping can greatly reduce this “urban heat island” effect. And LID tools help support enhanced landscape using natural water sources.

How LID Works

While conventional management strategies treat stormwater as waste to be eliminated as quickly as possible, LID recognizes it as a resource that can utilize rain close to its source to support landscape vegetation and a downstream stormwater runoff regime that more closely reflects predevelopment conditions. LID is adaptable and scalable to a broad range of land uses and project types.

Increased storm runoff is directly related to the amount of the impervious services in an area and how land has been developed and improved. The tools identify as design elements that can be crafted to greatly enhance design appeal by marrying form and function with the movement of water across a site. Bioswales, landscape catchments, curb cuts, cisterns, and porous pavements are just a few of the tools the Toolkit suggests. These features provide multiple benefits for city residents and businesses by reducing the cost of storm infrastructure, and increasing the quality of life and property values, and by improving streets, parks, and home landscapes.

LID tools included in the Mesa LID Toolkit are based on best practices that have been developed throughout the country, refined to work in the Desert Southwest. Several resources are available for more information about LID, stormwater management in urban landscapes, and green infrastructure. These include research and professional organizations such as American Society of Landscape Architects, the Environmental Protection Agency, and others. The Watershed Management Group is actively developing pilot projects and testing best practices in desert southwest landscapes. Learn more about their Green Streets Primer here.

In summary, LID provides a user-friendly and local mechanism for helping manage flood risk and improve the quality and uses of urban stormwater runoff. The application of LID can yield multiple benefits for cities, communities, businesses, and homeowners by creatively integrating naturally occurring rainfall into visible and functional landscapes that balance the needs of people and environment. The Mesa LID Toolkit provides an easily understandable graphic presentation of what LID is and how it can be used to improve the urban environment.  More information and a copy of the Mesa LID Toolkit is available at MesaAZ.gov.

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Craig Coronato, FASLA, LEED-AP

Craig Coronato, FASLA, LEED-AP