Miscellaneous runoff reduction practices

These runoff reduction techniques as less popular than rain barrels or rain gardens, but offer a way to adapt projects to fit the individual needs of a site. 

Canopy provision (Tree planting) 

This best management practice or BMP, includes planting canopy trees such that their canopy will grow to cover impervious areas. As rain falls on the tree, it will cling to the leaves and be absorbed in a process called "interception." In most of Chattanooga's rains - which are under 1 inch, most or even all of the rain hitting the trees will be captured and evaporated back into the atmosphere. 

• Trees planted must be over impervious surfaces to qualify for this rebate.

 Impervious surface reduction (Pavement removal)

  Impervious surfaces are surfaces that water cannot get through or soak into.These have become more common as civilization expands and continues to develop more roads, buildings, and surfaces covering the ground. When water can't get through, the build-up of pollutants on these surfaces gets swept off when it rains, contaminating the surrounding areas and going into creeks and streams. The City may consider supporting the removal of impervious surfaces such as pavement or driveways, or replacement of these surfaces with semi-permeable surfaces such as permeable paving or grassy pavers.

 Bioswales

 Bioswales are vegetated channels that provide treatment and retention to stormwater runoff as it moves through them. They help slow the movement of the water, help infiltrate it into the ground, and allow pollutants to filter. 

 Filter Strips 

 Vegetated filter strips are vegetated surfaces that are designed to treat sheet flow from adjacent surfaces. Filter strips function by slowing runoff velocities and filtering out sediment and other pollutants, and by providing some infiltration into underlying soils. Filter strips were originally used as an agricultural treatment practice, and have more recently evolved into an urban practice.

 Retentive Grading 

Retentive grading is a series of small depressions and berms (artificial ridges made of ground) that help slow or detain stormwater runoff. These dips and ridges are subtle, leaving the lawn looking relatively the same as one without. 

Infiltration Trenches

An infiltration trench is a rock-filled trench with no outlet that receives stormwater runoff. Stormwater runoff passes through some combination of pretreatment measures, such as a swale and detention basin, and into the trench. There, runoff is stored in the void space between the stones and infiltrates through the bottom and into the soil matrix. The primary pollutant removal mechanism of this practice is filtering through the soil.