Better site design

Increases in the quantity, rate, and frequency of runoff can be linked to two root causes:

1. the conversion of undeveloped or agricultural land cover to urban uses, and
2. the application of storm sewer systems.

The goal of LID site design strategies is to minimize these two sources of hydrologic impacts. Avoiding downstream impacts through non-structural, innovative site design methods is more economical, operationally efficient, and aesthetically pleasing than concentrating all stormwater management efforts on treating and controlling runoff downstream.

Site designers should exhaust all opportunities for non-structural methods to prevent runoff from being generated before determining how to mitigate the land cover change and storm sewer impacts through structural LID practices and detention ponds.

LID site design strategies can be grouped into four themes:

1. Preserving existing hydrologic features and functions;
2. Siting and layout of development;
3. Reducing impervious area; and
4. Using natural drainage systems.

The strategies need to be considered together as they all overlap and relate to each other. For example, preserving a natural channel will impact the layout of the site, and the layout of the site determines the extent of impervious area and optimal locations of structural BMPs.

The portion of water precipitated onto a catchment area, which then flows as surface discharge from the catchment area past a specified point.

Water from rain, snow melt, or irrigation that flows over the land surface.

Low Impact Development. A stormwater management strategy that seeks to mitigate the impacts of increased urban runoff and stormwater pollution by managing it as close to its source as possible. It comprises a set of site design approaches and small scale stormwater management practices that promote the use of natural systems for infiltration and evapotranspiration, and rainwater harvesting.

The temporary storage of stormwater to control discharge rates, and allow for sedimentation.

A hard surface area (e.g., road, parking area or rooftop) that prevents or retards the infiltration of water into the soil.