According to the EPA, stormwater is,
"generated when precipitation from rain and snowmelt events flows over land or impervious surfaces and does not percolate into the ground. As the runoff flows over the land or impervious surfaces (paved streets, parking lots, and building rooftops), it accumulates debris, chemicals, sediment or other pollutants that could adversely affect water quality if the runoff is discharged untreated."
In Ann Arbor, all stormwater (and any pollutants carried by storm water) are discharged, untreated, to the Huron River and its tributaries.
The stormwater drainage infrastructure in Ann Arbor includes:
The system is managed by multiple owners and operators including the City of Ann Arbor, Washtenaw County and the University of Michigan.
Why is stormwater a problem?
Both the quantity and quality of stormwater runoff can negatively impact the local water resources that provide drinking water, recreation and wildlife habitat.
Water Quantity - Once land is urbanized, very little water is able to infiltrate into the ground, and instead, is rapidly conveyed via storm drains or surface runoff to the nearest water resource. Higher volumes of stormwater runoff can cause flooding, erosion, and property damage. This results in significant changes in stream flow and wetland hydrology, which can cause stream bank erosion and loss of aquatic habitat.
Water Quality - Stormwater runoff picks up anything in its path and delivers it to the nearest creek or river. The pollutants carried by stormwater can degrade the quality of our waterways, making them unhealthy for people, aquatic life, and wildlife. Stormwater from the initial half inch of rain tends to carry the most pollution as it washes fertilizers, automotive fluids, animal waste, deicers, and dirt from the land surface into the storm drains.
Urban watersheds typically exhibit:
Increased run-off volume due to greater impervious surface and lower tree canopy
Increased peak discharge rates due to highly efficient drainage systems
Diminished baseflow, or dry weather flow, due to decreased groundwater infiltration
Stormwater management is any vegetative, structural, or managerial practice used to treat, prevent, or reduce the volume of runoff water that impacts surface or groundwater. The City of Ann Arbor works to manage stormwater in conjunction with land use change in order to protect water quality and reduce impacts of stormwater on local water resources.
What is the City doing?
Stormwater rates and credits
Learn about Ann Arbor's tiered stormwater rate structure, which is based on a property's amount of impervious surface.
Credits could help property owners reduce their rates:
Find out how the City of Ann Arbor works with other Middle Huron River Watershed partners to meet
state and federal stormwater permit regulations.
Stormwater Management Requirements for Residential Construction
A stormwater management plan is required for residential construction projects with 200+ sq. ft. of impervious surfaces. Learn about the code changes and download an impervious area worksheet to determine the code affects your project.