Low Impact Development Practices
Green Solutions to Site Design and Project Construction
May 27, 2009
Land developers are always looking for an edge in an increasingly competitive market. The ideal goal is to decrease site development costs and the time it takes for project permitting, while increasing public acceptance and market approval. One way to accomplish these objectives is by using Low Impact Development practices in planning and implementing projects.
Low Impact Development (LID) practices are the nuts-and-bolts techniques used by savvy land planners in designing sustainable developments. Many were pioneered in Europe (Germany particularly is an active player in this field). Prince George's County, Maryland adopted and then adapted the practices for use in the United States. LID practices are most effective in helping control a project’s stormwater runoff, from point of origin to final outlet. There are several underlying LID principles.
Low Impact Development Practices Conserve Natural Areas
First, conserve the site’s natural areas. Undisturbed woodlands, meadows, and drainage courses capture runoff, filter pollutants, and prevent erosion.
Stormwater Low Impact Development Practices
Next, disconnect stormwater flow. LID practices route runoff from hard surfaces to pervious areas, avoiding paving and pipe systems where possible. Conventional development practices treat water like a pollutant, using gutters and pipe systems to move it rapidly off-site. LID practices encourage developers to manage water as a resource. They capture the water at its source, slow it down, and create opportunities for it to infiltrate into the ground.
Stormwater impacting a site occurs first as rainfall. LID defenses first come into play here. The most effective LID option is to save as much undisturbed natural cover as possible. Mulch or temporary grassing can protect freshly graded ground until permanent landscaping is installed. Native or naturalized plants suitable to the region are easier to establish, and cost less to maintain. Undisturbed vegetative cover and appropriate landscaping are front-line defenders in the battle to control stormwater, helping to prevent erosion and protect property downstream. They'll nip a lot of potential problems in the bud.
Green Roofs
Some developers are now using green roofs to cover primary residences and commercial buildings. Green roofs act as biological cushions to subtract energy from falling rain. Plants growing on the roofs absorb some water, and the remainder drains from the roof at a slower rate.
Low Impact Development Practices Utilizing Biological Treatment
Once on the ground, the water flows into other LID features in the stormwater chain. Bio-retention facilities and rain gardens intercept the water, and then use the natural chemical, biological, and physical characteristics of plants, soil and mulch to absorb and neutralize pollutants. Treated water stored in these facilities soaks into existing ground or a prepared sub-surface. Infiltration basins and constructed wetlands can also be used to capture and filter runoff.
Cisterns and Rain Barrels
As an interim step in the stormwater chain, developers can install cisterns and rain barrels at downspouts, and collect and store the runoff for irrigation or washing cars. Land planners can help decide which LID practices to use for any situation.
Pervious Paving and Grass Swales
Some rainfall will fall on drives, patios, walkways, and other hard surfaces. Installing pervious concrete or paving blocks gives runoff from these surfaces another opportunity to infiltrate.
Design hard surfaces to direct remaining water to minimum-sloped grass swales. An undulating swale increases the time stormwater remains in contact with the ground. This enhances the chances for infiltration. Swales transport excess water to bio-retention ponds, infiltration basins or constructed wetlands, for further treatment and infiltration.
Low Impact Development Practices Benefits
What are the bottom-line benefits obtainable from using LID practices? For one, land developers may save money. Applying LID techniques to control water quality and peak discharge could eliminate detention ponds, or reduce their size. Eliminating pipes and paving saves construction costs.
A well-planned sustainable project that preserves natural area also tends to cluster land uses. Clustering allows land developers to build less infrastructure.
Preserving natural area also means a more aesthetically pleasing, marketable product. And rainwater stored in cisterns is available for irrigation – saving the cost of municipal main line water. These factors contribute to quality of life in the community, allowing land developers to set higher sales prices.
Spending less, while earning more, equals higher profits. And don’t overlook the community goodwill generated for environmental sensitivity.
The Down Side to Low Impact Development Practices
There are potential snags. Not all ordinances recognize LID technical solutions as viable stormwater controls. And some urban infill sites may be unsuitable for LID solutions due to the intensive nature of the development.
But change is on the horizon. Regulatory agencies are looking closer at the benefits of LID practices, and sustainable development in general. The public demands that developers protect property values and the environment. Lenders look kindly on projects designed as sustainable, integrating human spaces seamlessly into natural places. Done right, these projects cost less to develop. The market is attracted to well-designed conservation communities that include protected areas, thoughtful amenities, and mixed uses, while preserving the character of the land.
Increasingly, developers are looking for solutions that save water, time and money – and aid them in building reputations within their communities as stewards of the land. In the competitive world of land development, utilizing LID techniques in projects will allow land developers to meet these goals and deliver a project responsive to the needs of regulators, the public and the market – all while honing an edge just a little finer than their competition.
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