Planning Strategies
Low Impact Development
Low Impact Development (LID) is an approach to site planning design and is also sometimes termed Conservation Design. The objective of LID is not to avoid development or to alter the building program, but rather to accomplish the building program under the existing zoned densities in ways that reduce site impacts, especially impacts to stormwater quantity and quality.

LID is an innovative stormwater management approach built on the basic principle to manage rainfall at the source using uniformly distributed decentralized micro-scale controls. The goal of LID is to mimic a site's predevelopment hydrology by using design techniques - small, cost-effective landscape features - that infiltrate, filter, store, evaporate, and detain runoff close to its source, usually at the lot level.

While LID typically translates into reduction of imperviousness, this strategy also includes conservation of natural features, hydraulic disconnection, disbursement of runoff, bioretention, grass swales and channels, rain barrels and cisterns, vegetated roof gardens, Green Solar Canopies, permeable pavements, and vegetated filter strips.

Cahill Associates applied LID stormwater management techniques for a proposed 259-unit residential development of a 59-acre site in Campbelltown, Pennsylvania. The stormwater design incorporates several LID and sustainable stormwater management techniques, including infiltration beds under vegetated areas, infiltration beds under porous and traditional asphalt, swale/trench systems along the roadways, surface infiltration basins, infiltration trenches,vegetated swales, and disconnection of rood leaders. These BMPs are capable of permanently retaining and infiltrating the 2-year storm, resulting in zero site runoff.

For Pennsylvania State University, Berks Campus, Cahill Associates applied Low Impact Design concepts to the design of Dormitory Buildings and expanded parking area serving 400 new resident students. The new dorms were carefully situated along contours in the woods, with significant tree preservation up to 15' of the structures. Roof leaders discharge stormwater to a subsurface infiltration bed located beneath the walkways, or into a perforated pipe situated laterally along the contour in the preserved woods. Parking lots were constructed using porous asphalt pavement underlain by subsurface infiltration beds.

For more information on these and other LID projects, contact Cahill Associates.
Applications

At the Pennsylania State University, Berks, this new dormitory was constructed within 10 feet of an existing wooded stand.