LID SITE PLANNING PRACTICES

Low Impact Development (LID) site planning practices focus on preventing excess stormwater runoff at the source rather than addressing it after development occurs. This contrasts with structural Green Infrastructure (GI) practices, which are often used as retrofits or mitigation measures. While structural GI elements remain important in the final phases of development, LID site planning begins at the earliest stages to minimize runoff from the outset.

Key objectives of LID site planning include:

• Preserving natural areas and maintaining existing flow paths
• Reducing and disconnecting impervious surfaces
• Minimizing soil disturbance and compaction
• Restoring previously impacted areas

The first three principles are most effective when integrated early in the design process and revisited throughout development. The fourth applies specifically to sites that have already undergone some form of environmental disruption.

Site Analysis
A comprehensive site analysis is the foundation of LID planning. Understanding the natural features of a site early in the process leads to a more efficient design and prevents unnecessary environmental and financial costs. Each site is unique, and a thorough assessment avoids imposing a rigid design that disregards local characteristics.

Key attributes to assess include:

• Floodplain boundaries based on existing maps
• Riparian habitat and shallow groundwater identified via regional maps and aerial imagery
• Natural drainage paths, swales, and depressions using topographic data
• Soil characteristics and infiltration potential from resource maps, site inspections, or testing
• Steep slopes that impact water flow and erosion potential
• Native vegetation, particularly protected or endangered species
• Existing utilities, easements, and sensitive areas (cultural sites, conservation lands, viewsheds)
• Previously disturbed areas that may be repurposed for development

Conservation Opportunities
The most effective conservation efforts occur at the earliest planning stages, such as rezoning or block platting. Understanding regional watershed dynamics helps integrate site-level planning with broader environmental goals. Watershed management studies provide insight into connectivity and stormwater infiltration opportunities, particularly in arid regions where preserving existing drainage patterns is crucial.

When possible, LID strategies should align with broader community design objectives. At a minimum, they should incorporate regional watershed influences into the site plan to enhance environmental resilience.

Key Design Features
To maximize LID effectiveness, site design should incorporate:

• Setbacks from natural flow paths to preserve hydrologic function
• Compact development footprints using multi-story structures and clustering to minimize land disturbance
• Reduction of impervious surfaces by integrating landscaped stormwater conveyance features

Each strategy influences the others. For example, preserving a drainage path alters site layout, which then dictates impervious surface placement. Reducing pavement through permeable materials and landscaped swales further minimizes runoff and allows for natural infiltration. These considerations lower the need for costly engineered drainage systems while improving stormwater management.
Collaboration among engineers, landscape architects, and hydrologists is key to integrating LID effectively. When these disciplines work together from the outset, the result is a development that enhances environmental and economic value for the community.

Site-Specific Design
Once a site’s ecological and hydrological characteristics are understood, their influence on the development should be carefully assessed. For example, if two areas contain native vegetation but only one can be preserved, choosing the one that maintains connectivity within a larger wildlife corridor will have a greater ecological benefit.

Set-aside areas should be clearly marked on construction plans, and road networks should follow natural drainage patterns. Designed swales can serve as both stormwater conveyance systems and wildlife corridors, as well as provide recreational and aesthetic benefits. Addressing these considerations early prevents costly changes later.

Traditional developments often replace natural channels with rigid concrete infrastructure, leading to habitat loss and increased runoff. Instead, parks and green spaces can be positioned at the end of drainage corridors to enhance LID benefits.

Strategic placement of buildings and infrastructure can optimize stormwater management. Placing elements that generate runoff (such as roofs and sidewalks) at higher elevations allows gravity to direct flow toward landscaped infiltration areas. Curved vegetated swales slow water, promote infiltration, and improve water quality before it exits the site.

Compact building design also contributes to LID goals. A two-story structure can cut building footprint in half compared to a single-story alternative, preserving more permeable land area. Structural GI elements, such as permeable pavement and green roofs, should be incorporated into the initial design rather than added later as retrofits.

Unique Opportunities
Some sites contain previously disturbed areas that provide ideal locations for new development, reducing the need for further environmental disruption. These areas can also be restored to enhance wildlife corridors, improve floodplain function, or create community amenities.

For roadway projects, LID opportunities may be limited by right-of-way constraints, but reductions in impervious surface can still be achieved. In some cases, planned road widths can be reduced if master plans are outdated. Using vegetated swales instead of curb-and-gutter designs allows for natural infiltration and decreases the need for expensive drainage infrastructure.

Benefits of LID Site Planning
LID practices often produce overlapping benefits. For example, directing runoff through vegetated swales into a preserved natural area achieves multiple objectives:

• Slows runoff and improves infiltration, reducing stormwater infrastructure needs
• Supports vegetation growth, which cools the site and mitigates the urban heat island effect
• Enhances soil quality, further improving filtration and reducing off-site water flow
• Provides habitat for native species, benefiting biodiversity

Other key benefits include:

• Water quality improvement: Native vegetation and soils filter pollutants before they reach water bodies.
• Habitat enhancement: Increased vegetation volume provides shelter and food for wildlife.
• Air quality benefits: Plants remove airborne pollutants through natural processes.
• Carbon sequestration: Native plants and soils store carbon, helping mitigate climate change.
• Urban cooling: Trees and vegetation reduce temperatures and provide shade, making communities more comfortable in hot climates.

Considerations During Construction
Pre-construction meetings with developers, contractors, and local officials ensure LID principles are understood and followed. Training sessions for all workers should emphasize the importance of preserving sensitive areas and outline prohibited activities. Providing illustrated guides can help reinforce these practices and ensure continued adherence throughout the project.

By integrating LID practices from the earliest planning stages through construction, developments can achieve long-term sustainability while reducing environmental and economic costs. These strategies are particularly valuable in arid regions, where preserving natural drainage systems and minimizing water loss are critical for resilience.