 |
31% of Ann Arbor is covered by impervious surface. (Note that this analysis does not include streets or rights-of-way.) The City adjusted its stormwater rate system in 2007 to provide incentives for reducing imperviousness.
Source: 2004 State of Our Environment |
|
Imperviousness for Ann Arbor* |
| Total Area |
|
|
| Water |
415 |
3% |
| Impervious Area |
4,616 |
31% |
| Pervious Area |
9,795 |
66% |
| *This analysis does not include streets or rights-of-way. |
What is impervious surface?
An impervious surface is any surface that does not allow water to be absorbed into the ground. In Ann Arbor, there are many impervious surfaces, including roadways, parking lots, sidewalks, driveways and roofs of buildings and homes.
How does impervious surface affect the environment?
Studies have shown that the health of streams begins to decrease after 8% of their watershed is rendered impermeable.
- Streambeds may experience considerable erosion as a result of high stormwater flows. In particular, small stream channels cannot accommodate such unnaturally high flows of water. The sediment dislodged by this erosion is a significant non-point source pollutant, which degrades the habitat quality for aquatic organisms.
- Stormwater runoff that flows over concrete is frequently much warmer than groundwater and will increase the water temperatures. Warm water cannot hold as much oxygen as cold water so the temperature change is an additional stress to many native aquatic species.
More information
- Ann Arbor Stormwater and Stormwater Rates Site