Human development that minimally disturbs the flow of water in the landscape is nothing new. Think of cave dwellings or tee-pees on the plains, for instance. However, as urban and suburban areas expand and more of the Earth’s surface is graded and paved, our impact on natural water systems has become increasingly problematic. Water continues to fall on the landscape as precipitation, but where and how it flows after it lands can be vastly different for a drop of water that falls on a developed landscape.
Urbanized areas are typically designed and engineered to transport water away from buildings and people as swiftly and efficiently as possible. Water that falls on a city lot flows either directly to the sewer or storm drain system from the roof or landscape via a drain, or it runs into the street. Streets act as water conveyance systems that collect all runoff water in gutters and distribute it to storm drains. Usually this water is transported to the edge of the city in a separate storm sewer system, and then dumped into a water body such as a creek, river, wetland, lake, or the ocean.
When runoff water enters these water bodies, it does so in a different way than it would in a natural system. For one, it is carrying pollution that it picked up on the way, including volatile organic compounds and heavy metals from automobiles and fertilizers, as well as debris and fecal matter. Unlike natural watershed systems, the storm drain system does not provide an opportunity for such pollutants to be filtered in the landscape. Stormwater from storm drains also enters water bodies more rapidly and in greater volume than it naturally would. This results in increased flooding downstream, as well as erosion and siltation problems. Furthermore, valuable ecological habitat and ecosystem services are lost as natural creeks are buried underground to become storm drains, rivers are channelized, and wetland areas are paved over and marginalized.
Low Impact Development (LID) is a response to these conditions of development, seeking to create a new development regime that preserves natural hydrologic function as much as possible. Instead of trying to mitigate affected water bodies downstream, LID treats water in the landscape close to where it falls. In LID, according to Coffman (2000), “Hydrologic functions of storage, infiltration, and ground water recharge, as well as the volume and frequency of discharges are maintained through the use of integrated and distributed micro-scale stormwater retention and detention areas, reduction of impervious surfaces, and the lengthening of flow paths and runoff time.” LID also incorporates preservation for high-value and sensitive ecological site features such as riparian buffers, wetlands, steep slopes, mature trees, flood plains, woodlands and highly permeable soils (EPA 2000). Typical components of LID include: vegetation, including trees, living roofs, and vegetated swales; permeable pavements; bioretention systems such as rain gardens, bioswales, buffer strips, dry wells, etc.; and stormwater capture for later use, such as with rain barrels, tanks, or cisterns (EPA 2000).
LID has only been around for a short while in the United States, but momentum is growing rapidly. The early adopter of LID in the US was Prince George’s County, Maryland, who pioneered techniques and implemented test projects during the 1990’s. Over the last 15 years LID has spread to other parts of the country, including California. Local governments have begun to incorporate LID into their Stormwater Management Plans (SWMP) which are required along with NPDES (National Pollution Discharge Elimination System) permits by the EPA for cities and counties with municipal separate storm sewer systems (MS4). SWMP’s are required to address pollution levels in water bodies and establish total maximum daily loads (TMDL’s) for pollutants, but the means of enforcement by which these water quality improvements are achieved are largely up to local governments. LID, when incorporated into new developments and retrofits, can be a cost effective and sustainable way to accomplish water quality goals. Additionally, the EPA is encouraging communities to use Green Infrastructure, which overlaps with LID in application, to meet Clean Water Act requirements such as NPDES permits, and has issued a Strategic Agenda to that end. The EPA hopes to have a final ruling to enforce green infrastructure by the end of 2012.
I recently had the opportunity to attend a forum put on by Wholly H20 entitled “Incorporating Low Impact Development (LID) into Municipal Stormwater Management.” The forum had a panel of speakers that included city, county, nonprofit, and federal stormwater policy experts from the Bay Area. I got to see a number of examples of LID projects in the Bay Area, as well as hear about various policy strategies. Governmental forerunners in the Bay Area include San Mateo City and County Association of Governments (C/CAG) and San Francisco Public Utilities Commission (SFPUC), both of which have worked hard to encourage LID through publishing guidelines, creating regulations and implementing demonstration projects. San Mateo County has a provision that enforces LID through NPDES permitting, with checklist categories that include site design, stormwater treatment, and hydromodification controls. The requirements for including these features are based on the proposed change in impervious area of a development. Additionally, any small project must include at least one LID measure. C/CAG has been able to fund numerous LID projects through a countywide vehicle registration fee that funnels money to stormwater management. Similarly, San Francisco has a Stormwater Management Ordinance (2010) that ensures that any development that disturbs over 5,000 square feet must incorporate LID-style stormwater management. In addition, numerous other sustainable stormwater management projects, such as Doyle Hollis Park in Emeryville, have been implemented throughout the Bay Area with the help of nonprofit organizations.
Design Ecology strives to be at the cutting edge of low impact development and green infrastructure. By retrofitting buildings with living roofs, we are demonstrating integrated ways that development can contribute to reduced runoff and cleaner stormwater. Other benefits of an integrated green infrastructure approach include reduced energy costs, reduced water demand, providing habitat for native species, reducing the heat island effect, and a more beautiful and inviting urban environment. We are currently working with the Sonoma County Water Agency (SCWA) to create a demonstration of LID in action at their offices. SCWA has recently published their Water Smart Development Guidebook, which includes LID practices. The City of Santa Rosa also has an LID Technical Design Manual, which provides more specific tools to meed NPDES requirements. The SCWA campus looks to demonstrate principles of these guidebooks by capturing, treating, and infiltrating as much stormwater onsite as possible. Some strategies might include rain gardens, bioretention swales, permeable paving, and water storage.
Water should be treated as a valuable resource rather than a nuisance. By designing with LID principles we can contribute to changing the pattern of development and its impact on natural water cycles. Not only that, but designing this way allows us to tap into a free and abundant resource that can enhance our lives and contribute to sustainability in our built environment. By taking full advantage of water resources on-site, our structures and landscapes can become more productive, more efficient, more beautiful, and more integral to the ecological systems that surround and support us. In this way, we hope the nature of human development will soon surpass even “low impact”, to become “high benefit”.