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Thursday, November 17, 2016

An Engineered Approach: Integrating Low Impact Development for Sustainable Growth

Vegetated Swale

A LID practice to decrease the quantity and increase the quality of stormwater runoff.

"P1000808" by Thomas Le Ngo

Written by Ryan Bare, Research Assistant, Hydrology and Watersheds, and Satish Ravindran, P.E., CEM, LEED Green Assoc., Senior Research Associate, Clean Energy Technology

The Need for Low Impact Development
Throughout the history of civilization, humans have altered, managed and controlled our environment with fire for agricultural land clearing, animal domestication, and the building of cities. Population growth and expanding development are often accompanied by the negative effects of urban sprawl. Atmospheric greenhouse gases have also substantially risen in the past 70 years, alongside global population growth. These and other deleterious effects of growth are amplified around concentrated human populations in large urban centers.1 Continuing in this trend, the Houston-Galveston region is projected to grow by more than 3.5 million people in the next twenty years. Rapid urbanization and densification of neighborhoods will bring with it more impervious surfaces and loss of vegetative cover. Additional impervious cover increases stormwater runoff, flooding low-lying areas and degrading water quality in our bayous and Galveston Bay.

Houston’s stormwater code requires conventional methods of stormwater management such as detention ponds and storm sewers. Existing stormwater infrastructure struggles to drain the enormous volumes of runoff from major rain events, as illustrated by the flooding that occurred in 2015 and 2016. One potential solution is to integrate Low Impact Development (LID) stormwater management practices with our built environment. LID offers a suite of engineered and applied practices that promote sustainable growth, improve community health and wellbeing, and foster economic prosperity.

What is Low Impact Development?
LID practices are designed to mimic natural hydrological and ecological processes that promote retention and infiltration of stormwater on site. This serves to reduce the overall volume of runoff and improve the quality of water that does flow from the site as runoff. LID is gaining interest because the ecological engineering approach provides tools for cost-effective management of stormwater at the point of origin. LID encourages residents, developers and municipalities to incorporate stormwater management practices such as bioretention systems, rainwater harvesting, permeable pavements, green roofs, and vegetated swales into their landscape or development projects. The primary objective is to preserve the original hydrology (how water flows) of the project site by incorporating native vegetation and natural landscape features. Incorporating LID practices into a project can generate economic and environmental benefits for developers and communities.

Economic Benefits of LID
LID practices can leave more developable land per parcel compared to traditional practices that require unsightly, acreage-intensive detention basins. Less detention means a reduced cost per parcel for drainage infrastructure. In a study comparing traditional development practices with LID, the Houston-Galveston Area Council estimated that LID could result in an additional 24,000 square feet of leasable floor space and save 15% in landscaping and stormwater infrastructure costs for an eighty-acre commercial site.2 To encourage sustainable growth, smaller parcels can be engineered using LID design techniques that benefit the developer’s bottom line. Municipalities can also utilize LID to naturalize and modernize roadway development projects. The installation of a center median vegetative swale coupled with a High Performance Modular Biofiltration System instead of a traditional storm sewer saved Harris County 7% per mile in roadway construction costs.3 Other developer benefits include reduced land clearing and grading costs, increased project marketability, improved aesthetics, lower maintenance costs, and generation of green jobs.

Environmental and Community Benefits of LID
A variety of environmental and community benefits can be achieved by incorporating engineered green space at the site or neighborhood scale. Infiltration is often disrupted by impervious land cover such as roadways, parking lots and sod lawns. In a 2009 study of a residential roadside bioretention project, the average annual stormwater volume was reduced by approximately 64% and a peak flow reduction of 60 to 70% was achieved.4 Many LID practices mimic natural hydrologic patterns while reinfusing the landscape with once abundant native vegetation. The preservation and restoration of native vegetation is a core LID principle that promotes human health and wellness by integrating walkable green space into urban environments. Residential and commercial parcels developed with LID practices have more park and green space. This sustained nearness of nature translates to higher social capital, stress reduction and enhanced community economics.5 Preserving the original hydrology of the site and incorporating native vegetation also enables stormwater to infiltrate below the ground surface. Properly engineered and maintained LID infrastructure is a powerful tool for urban stormwater management that promotes infiltration and groundwater recharge as well as environmental, economic and societal well-being. Supplanting impervious cover with vegetation and permeable surfaces should also reduce energy consumption and other inputs, thereby reducing greenhouse gas emissions.

The State of LID in the Houston-Galveston region

As we consider the potential impacts of growth, past, present, and future, humankind is at a crossroads. We can either become better stewards of the earth or continue with business-as-usual.1 We must move past merely thinking about sustainability to becoming a society that lives, acts, and builds sustainably. The benefits of incorporating sustainability in our region are evidenced in approximately 75 LID projects and have been implemented or are currently in design. However, to achieve optimized benefits on a watershed scale, LID must become the new normal. LID practices are part of the solution to balance development with healthy natural and societal systems. Everyone stands to benefit from smarter water resource management that incorporates LID to reduce flooding and pollution with robust, sustainable stormwater infrastructure. An engineered future that integrates LID and green infrastructure starts with a vision to manage urban development with progressive city and county ordinances, and making smarter decisions on every parcel of land. Increased green infrastructure throughout the region will multiply the collective benefits for communities, the environment and the economy.

For a closer look at LID in our region, select a blue pin for project specific LID features. Click to view map in an independent tab.

More Information
For an in depth discussion on the state of LID incentives in Houston see: Incentives for Natural Drainage Systems in Houston Area Development Projects?

To find out what kind of incentives can encourage adoption of LID practices and what may work for our region see: EPA Low impact Development Incentives.

To explore how one can incorporate LID practices in a development project see: Harris County Low Impact Development & Green Infrastructure Design Criteria for Storm Water Management.

1Steffen, W., P. J. Crutzen, and J. R. McNeill. 2007. The Anthropocene: Are humans now overwhelming the great forces of nature. Ambio 36:614-621.
2Houston-Galveston Area Council. Designing for Impact: A Regional Guide to Low Impact Development, 2016. http://www.h-gac.com/community/low-impact-development/documents/Designing-For-Impact-Guide-for-Governments.pdf
3Anthony Kendrick, ENV SP. Lessons Learned from LID-Based Roadway.
4Tetra Tech. 2009. City of Toledo, OH, Maywood Avenue Stormwater Volume Reduction Project Plan Set.
5Kathleen L. Wolf, Ph.D. Encouraging Human Health and Wellness: LID Planning & Design for Co-Benefits, 2015.