1. I don’t see that any rain leaves my yard when it rains, and my gutters drain into my lawn. Why doesn't my lawn and garden areas count as stormwater BMPs so that I can get a credit?
While a rain shower of a few tenths to one quarter of an inch may not result in visible runoff, there are several reasons that lawns and gardens do not function as adequate stormwater BMPs. Typically, soil in a yard is heavily compacted. The roots of common turf grasses and many garden plants are very shallow, therefore not capable of absorbing much moisture. During heavy rains, these areas become saturated beyond capacity, not allowing them to retain moisture. This generates runoff that is transported to receiving bodies of water. Stormwater BMPs, like rain gardens or sand filters, are designed to allow filtration and infiltration of stormwater runoff, thereby helping to reduce the transport of pollutants to area lakes and streams.
2. If pervious pavers qualify as a stormwater BMP, why do existing gravel driveways or brick patios and sidewalks count as impervious areas?
For pervious pavers to function effectively, both the surface and subsurface structure must be properly designed to allow for infiltration of stormwater runoff. A gravel driveway lacks this required substructure. Because the soils are compacted by vehicles, the surface becomes nearly as impervious as asphalt or concrete during a significant rain. For areas paved with standard bricks, lack of adequate spacing between individual pavers and the absence of a substructure properly designed to allow infiltration, results in a nearly impervious surface. Only those paved areas constructed with materials and techniques specifically designed to act as stormwater BMPs qualify for the Stormwater Quality Credits.
3. Does a rain barrel qualify as a Stormwater Credit?
Installation of one rain barrel alone does not qualify as a Stormwater BMP, however, for Residential parcels, a 40% credit can be obtained by installing 4 rain barrels on the parcel. A single rain barrel capacity is too small to have an appreciable effect on the quantity or quality of stormwater runoff from a site. During a one-inch rain storm, a 1,000 S.F. area will generate over 700 gallons of water and with an average capacity of approximately 50 gallons. Typical rain barrels are unable to adequately hold or treat this amount of runoff. Even if you don't have room for 4 rain barrels, a rain barrel or two is still an environmentally sound and useful tool for water conservation, by providing water to irrigate gardens between rains.
4. Why is there no credit on my bill if there is no rain?
The Stormwater Utility must maintain the stormwater conveyance system to be ready for the next precipitation event. During a dry spell, there is considerably more street sweeping done to remove debris and litter in the streets and the stormwater retention ponds require mowing and maintenance to the banks, while City bio-retention cells and rain gardens need ongoing maintenance. In addition, utility crews must inspect stormwater lift stations and stormwater outfalls that discharge the water to the Mississippi River to ensure proper functioning.
One of the more labor intensive maintenance items stormwater utility staff does is clean catch basins during and after a rain event. Debris clogs the catch basin grates inlet and slows or stops stormwater from entering the stormwater conveyance system and actually causes street flooding in some areas of the city. This debris is mainly grass clippings, leaves and debris from streets.