Water Services

Low Impact Development

picture: downtown nashville buildings water spraying trees

The LID (Low Impact Development) 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.

LID Manual 2016 (full version)

Green Infrastructure Practices (GIP's)

If a project 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 Steve Mishu.

Incentives

These are the incentives that are currently offered. Please check back for others.

Table 1. Green Infrastructure Incentives
Incentive	Requirement/Benefit
Stormwater User Fee Credit	Sites designed in accordance with the LID Manual can receive a 75% downward adjustment in their Stormwater User Fees.
Redevelopment Credit	Certain previously developed sites can meet a Runoff Reduction goal of 60% instead of 80%. A site must have a current, pre-development runoff coefficient (Rv) greater than 0.4 to qualify.
Green Roof Rebate	MWS provides a credit of up to $10 per square foot of green roof installed within the combined sewer system. The credit is applied to the site’s sewer bill for up to five years. Please visit the Green Roof Rebate page for more information.
Reduced Detention Requirement (see Chapter 3.2.5.)	Certain sites designed in accordance with the LID Manual can reduce their required stormwater detention quantity.

* Sites cannot receive both the 75% Stormwater Fee reduction and redevelopment incentives. Sites receiving the redevelopment incentives may still receive up to a 50% Stormwater User Fee reduction as outlined in the Stormwater User Fee Credit Manual.

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.

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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

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

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 & 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