Runoff Reduction & Green Infrastructure

Over the past 20 years of urban stormwater quality regulation, research and experience has lead to an emphasis on runoff reduction and green infrastructure as goals of stormwater management. The reason is that urban development otherwise seriously affects the hydrology of nearby streams. Increased imperviousness prevents ground infiltration of stormwater, which dries up seeps and springs and depletes streams of water in the summertime. Also, the greater volume and rate of runoff from impervious areas results in greater, more frequent, and more erosive flows in a stream.

On-site Management

Tennessee’s latest (2010) stormwater general permit sets forth a standard of on-site management of the first inch of rainfall: “this first inch of rainfall must be 100% managed with no stormwater runoff being discharged to surface waters.”

Achieving runoff reduction will rely on a combination of infiltration to the ground, evaporation, transpiration by vegetation, and rainwater harvesting and use.

Revising Murfreesboro’s runoff management standards

The City is drafting (June, 2015) changes to its stormwater ordinance to adopt the one-inch on-site management standard. But since much of the landscape in Rutherford County is karst, or because seasonal groundwater levels are near to ground surface (situations where concentrated infiltration is not recommended or infiltration will not occur), on-site management will not be a good option on all sites; so other options will be allowed.

UT and TDEC Guidance

Tennessee Permanent Stormwater Management

The Tennessee Division of Water Resources has released tools for design of permanent stormwater control measures, including TNRRAT design assessment tool, training videos and the Tennessee permanent stormwater management manual.

Environmental Protection Agency Resources