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What is stormwater?
Stormwater is runoff from rain or snowmelt that flows off streets, rooftops, and lawns into storm drains. From storm drains, runoff flows directly into streams, lakes and rivers. Unlike wastewater, which is treated at a wastewater treatment plant, stormwater receives no treatment before being discharged to surface waters. In Ann Arbor, all stormwater (and any pollutants carried by stormwater) are discharged to the Huron River and its tributaries. |
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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. Increased 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 Huron River. The pollutants carried by stormwater can degrade the quality of our waterways, making them unhealthy for people, fish, and wildlife. The initial half inch of stormwater tends to carry the most pollution as it washes fertilizers, automotive fluids, animal waste, deicers, and dirt into the street and down the gutter.
Urban watersheds typically exhibit:
- Increased run-off volume due to greater impervious surface
- Increased peak discharge rates due to highly efficient drainage systems
- Diminished baseflow, or dry weather flow, due to decreased groundwater infiltration
Managing Stormwater
Land use change from a natural to a more urbanized environment presents significant challenges for the management of aquatic ecosystems. 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.
Last Update: January 19, 2010