Low Impact Development Information for Developers

picture: downtown nashville buildings water spraying trees

The Low Impact Development (LID) Manual is a site design approach that utilizes Green Infrastructure to meet a development site’s post development stormwater runoff water quality requirements. This approach satisfies the new MS4 Permit requirement to infiltrate, evapotranspire, or harvest and use the first inch of rain.

Low Impact Development Manual 2021 (full version)

Green Infrastructure Practices

LID Manual Image

If a project in the MS4 area has sufficient site limitations that preclude it from meeting the Low Impact Development requirement, they will need to submit a Low Impact Development Waiver Application electronically to MWS LID Waiver ([email protected]). In certain cases where infiltration rates cannot be determined or a bioretention area is being placed on fill or in over excavated rock, there is a modified bioretention design that can be utilized.

Projects in the combined sewer area should contact MWS CSEP Projects ([email protected]).

Standard Drawings

If you are having difficulty opening the .DWG file format, follow the following steps:

Identify DWG file to download.
Right click link and select, “Save Link As.”
Navigate to the location you wish to save the file through the file explorer.
In the, “Save as type,” line item, select, “All Files.”
Manually type the .dwg file extension to the end of the file name.
Select, “Save.”

LID Site Design Tool

A Site Design Tool has been created to aid engineers in designing the water quality treatment for a project in accordance with the methodology in the LID Manual. This program can be downloaded onto your computer and used to calculate if a site meets Metro’s water quality requirements. To ensure we are able to send out any updates to this tool, we are now requesting you to enter your e-mail address before this tool can be downloaded.

Request the LID Site Design Tool

Rainwater Harvester

This cistern design tool was designed by Matthew Jones of NC State University and can help size a cistern, determine if it is meeting a site’s runoff reduction goal, and calculate the cost savings.

Rainwater Harvester - Cistern Design Model
Nashville's Rainfall Data - download to your computer
Nashville's User Manual - step by step instructions

building with 3 large cisterns courtesy of the Chesapeake Bay Foundation/cbf.org
Photo courtesy of the Chesapeake Bay Foundation

LID Manual Training Video

A training video was created to introduce the LID Manual methodology and describe how to design a site in accordance with the Manual. The video includes examples using the LID Site Design Tool. The video lasts approximately one hour and twenty minutes and the breakdown of the topics and their start times is listed below. The presentation is available for download in case you have trouble seeing the slides in the video.

Video time stamps and topics:

0:00:00 Overview of Green Infrastructure and the Runoff Reduction Method
0:28:52 Green Infrastructure Design Steps and Green Infrastructure Practices (GIPs)
0:45:54 LID Site Design Tool and Simple Example
1:02:07 Adjusted Curve Number
1:06:26 Nashville Site Example