Stormwater Management in Michigan: Why LID? - Low Impact Development and Sustainable Stormwater Management - page 217

The impacts of stormwater runoff
Stormwater runoff is rainfall or snowmelt that runs off the land and is released
into rivers and lakes. Problems related to stormwater runoff are most evident in
areas where urbanization has occurred. As mentioned above, the change in the
water cycle has a dramatic effect on our water resources. This impact is based on
both the quantity and quality of stormwater runoff reaching our rivers and lakes.
The impacts of stormwater runoff are well documented in Michigan and
throughout the country. They include:
• Increased flooding and property damage. Increased impervious
surfaces decrease the amount of rainwater that can naturally infiltrate into
the soil and increase the volume and rate of stormwater runoff. These
changes lead to more frequent and severe flooding and potential damage
to public and private property.
• Degradation of the stream channel. One result of runoff can be
more water moving at higher velocities through stream channels. This condi-
tion is called ''flashy flows'' and happens at increased frequency as an area
is developed. As a result, both the streambank and stream bed are eroded
more frequently. This can result in widening and deepening the channel, as
well as a decline in stream substrate quality, and degradation of habitat.
• Less groundwater recharge and dry weather flow. As impervi-
ous surfaces increase, the infiltration of stormwater to replenish groundwater
decreases. Groundwater is important because many people rely on ground-
water for their drinking water supply. In addition, the groundwater ''feeds''
rivers and lakes especially during the dry season to ensure a steady flow.
Streambank erosion and degraded habitat. Source : Wayne County Department of Environment.