Low Impact Development Manual
As of July 1, 2020, Utah’s Small MS4 permit and Jordan Valley Municipalities MS4 permits require retention of the volume associated with the 80th percentile storm event using LID practices for new and redevelopment projects greater than 1 acre. See part 22.214.171.124. of the permits:
As a community grows, vegetation is removed and the surface area is covered by parking lots, roads, and rooftops. Precipitation cannot soak through these hard (impervious) surfaces. Traditional storm water conveyance systems carry precipitation offsite through a conventional “collect-and-convey” system of pipes, ditches, and storm drains. The volume of storm water (runoff) that is discharged to and transported by municipal storm-drain systems is one of the main causes of water quality issues in most urban areas.
Low Impact Development Principles
Low Impact Development (LID) principles utilize storm water as a resource to retain precipitation onsite.
- LID costs less than conventional “collect-anrd-convey” systems because of fewer pipes, fewer below-ground infrastructure requirements and less impervious surfaces
- Space once used for storm water ponds can be used for additional development or conservation
- Precipitation infiltrates into the soil, reducing the volume of water flowing through the site, mimicking the site’s predevelopment hydrology
- Infiltration contributes to groundwater recharge
- Precipitation provides irrigation for trees and other vegetation, which in turn shades and cools streets, and increases property values in neighborhoods, commercial and industrial areas
- Fewer pollutants are caught up in the runoff and transported to receiving waters
- Other benefits include: improved wildlife habitat, thermal pollution reduction, energy savings, smog reduction, and enhanced wetlands protection
Examples of LID Techniques
LID principles mimic nature by using techniques that infiltrate, evapotranspire, and/or harvest/reuse the runoff generated.
Reduction of Impervious Surfaces
Minimize ground disturbance by identifying the smallest possible land area that is cleared, graded, and paved. Other examples of ways to reduce the amount of impervious surface on a site include narrow streets, shared driveways, and shared parking. Streets, roads, driveways, and sidewalks can be narrowed within the local zoning regulations.
A cluster development places homes closer together on smaller lots. Typically, the remaining 40% to 50% of the land in the development remains undeveloped, resulting in less ground disturbance.
Disconnect Impervious Areas
Runoff is redirected from roof leaders, roadways and other impervious areas onto pervious surfaces such as vegetated areas, reducing the amount of directly connected impervious areas and reducing the runoff volume and filtering out pollutants.
Bioretention–A bioretention area or rain garden is a shallow planted depression designed to retain or detain stormwater before it is infiltrated or discharged downstream. Evapotranspiration–Evapotranspiration (ET) is the sum of evaporation and plant transpiration from the Earth’s land and ocean surface to the atmosphere. Evaporation accounts for the movement of water to the air from sources such as the soil, canopy interception, and waterbodies. Hydrology–Hydrology is the science that includes the occurrence, distribution, movement and properties of the waters of the earth and their relationship with the environment within each phase of the water cycle.
- 2019 LID and Retention Training Presentation (10 MB)
- EPA’s Reducing Stormwater Costs through Low Impact Development (LID) Strategies and Practices (771 KB)
- Guide to Low Impact Development within Utah (10 MB)
- Low Impact Development Center
- Low Impact Development Center’s LID Urban Design Tools
- Jordan Valley Water Conservation Garden Park