Low+Impact+Development

A variety of measures can be implemented to optimize the landscape surrounding a building. Among these, preservation of existing landscape features should be the designer’s first course of action. Mature trees and vegetation are valuable resources that take many years to replace. Preserving them not only allows for their use in natural shading (and in some climates, as a wind break or shelter belt), it also maintains existing wildlife habitats, existing drainage patterns, and soil conditions. Tree preservation reduces the need for excavation, transportation, and relocation of soil. In addition, it reduces the need for supply and transportation of fill and landscape materials. When adding new vegetation to a site, use regionally consistent landscaping strategies, composed of locally grown, native plants.

Definition of Low Impact Design (LID)
Low Impact Development (LID) is a sustainable storm water management strategy that is gaining rapid acceptance in the United States to meet regulatory compliance and resource protection goals and is practiced extensively in Europe. The increased use of LID is in response to burgeoning infrastructural costs of new development and redevelopment projects, more rigorous environmental regulations, concerns about the urban heat island effect, and the impacts of natural resources due to growth and development. The frequency of droughts and concern about water quality issues have also prompted interest in the treatment and the reuse of storm water as a viable resource and has resulted in a shift in the way planners, developers, architects, engineers, and the public approach the control of storm water and conservation of rainwater. Many municipalities across the nation have embraced LID due to its holistic approach to site design and overall sustainable design. There are countless examples of jurisdictions that have proactively revised their development policies, codes, growth and management plans and implemented LID technologies to manage storm water at its source and collect rainwater for secondary use. The LID strategy controls water at the source—both rainfall and storm water runoff—which is known as 'source-control' technology. It is a decentralized system that distributes storm water across a project site in order to replenish groundwater supplies rather than sending it into a system of storm drain pipes and channelized networks that control water downstream in a large storm water management facility. The LID approach promotes the use of various devices that filter water and infiltrate water into the ground. It promotes the use of roofs of buildings, parking lots, and other horizontal surfaces to convey water to either distribute it into the ground or collect it for reuse. The LID approach differs from conventional conveyance systems as it promotes the highest and best use of the intrinsic land form and built structure(s) to both distribute storm water and collect rainwater. The uniqueness of LID is the interaction and function of water on a site. It capitalizes on the integration of infrastructure, architecture, and landscape in order to create a balanced, hydrologically functional and sustainable site. The LID approach handles water like the valuable and viable resource that it is, for the water that reaches a project site is a valuable commodity and can be used in innumerable ways. LID encompasses the use of structural devices (engineered systems) and non-structural devices (vegetated, natural systems). It uses a combination of these technologies, or a "suite of technologies," to maintain or restore the natural hydrologic functions on a site with the goal of reducing the impact of development. The goal is to structure the development of a site so that the pre-development conditions are not altered excessively. Of particular concern are the rate of storm water runoff, the pollutants in the water, and recharge of water into the ground. By reducing water pollution and increasing groundwater recharge, LID helps to improve the quality of receiving surface waters and to stabilize the flow rates of nearby streams. The integrated LID devices that are available allow the designer to restructure the built environment to control storm water and capture rainwater in order to minimize the impact of development. The integration of LID devices permits the developer and designer to use an array of storm water management devices that are both cost-effective and environmentally sound. The LID strategy is not a static design approach, however, is very dynamic and adaptable. LID has been proven to reduce development and infrastructure costs, minimize operations and maintenance costs, and improve the marketability of projects.  Fig. 1: Key Elements of LID The Benefits of LID
 * The primary benefits of LID are:
 * 1) To prevent degradation of water quality and natural resources,
 * 2) To manage storm water more efficiently and cost effectively,
 * 3) To protect groundwater and drinking water supplies, and
 * 4) To help communities grow more attractively.

Achieved through design to:
 * Reduce imperviousness by using permeable paving or landscaping to break up expanses of impervious surfaces.
 * Direct runoff into or across vegetated areas to help filter runoff and encourage groundwater recharge.
 * Preserve, or design into the infrastructure, naturally vegetated areas that are in close proximity to parking areas, buildings, and other impervious expanses in order to slow runoff, filter out pollutants, and facilitate infiltration.
 * Reduce street widths.
 * Remove curbs and gutters from streets, parking areas, and parking islands to allow storm water sheet flow into vegetated areas.
 * Use devices such as bioretention cells, vegetated swales, infiltration trenches, and dry wells to increase storage volume and facilitate infiltration.
 * Grade to encourage sheet flow and lengthen flow paths to increase the runoff travel time in order to modify the peak flow rate.
 * Disconnect impervious areas from the storm drain network and maintain natural drainage divides to keep flow paths dispersed.
 * Disconnect roof downspouts and direct storm water into vegetated areas or into water collection devices.
 * Install cisterns or sub-surface retention facilities to capture rainwater for use in irrigation and non-potable uses.
 * Install vegetated roofs or garden roofs.
 * Use native plants (or adaptable species) to establish an adaptable and low maintenance landscape that requires less irrigation and are appropriate for the climatic conditions.
 * Use naturally occurring bio-chemical processes in plants located in tree box filters, swales, planter boxes.
 * Divert water away and disconnect from the storm drain or CSO using correctional drainage techniques.
 * []