An Introduction to Stormwater
What is stormwater? Stormwater is exactly what it sounds like! Stormwater is the water resulting from rainfall and storms.
When it rains, stormwater can move in three ways:
- Rainfall can evaporate and go back into the atmosphere,
- Rainfall can infiltrate and nourish plants trees and can also replenish groundwater.
- Rainfall can runoff as "stormwater runoff." Stormwater runoff occurs in areas where surfaces do not allow for infiltration. Such surfaces are called impermeable or impervious, as they do not allow for water to permeate into the ground. Examples of impermeable surfaces include: parking lots, sidewalks, roads, and rooftops.
Picture courtesy of The U.S. EPA
Figure 1. Shows how runoff is increased (from 10% runoff to 55% runoff) with increases in impervious surfaces associated with urbanization.
Common Pollutants in Stormwater Runoff
Of evaporation, infiltration, and runoff, stormwater runoff is the least desirable. Stormwater runoff has been shown to cause a myriad of environmental and safety hazards such as: soil erosion, degraded lakes and streams, algal blooms and fish kills, and flooding.
Typically, as cities grow and urban sprawl continues to rise, more and more impermeable surfaces result in increased stormwater runoff. As the runoff travels across these impermeable surfaces, it collects pollutants such as dirt/sediment, motor oils, fuels and metals from vehicular use, trash, and nutrients from fertilizer. This polluted runoff then enters stormwater inlets, where it moves through a series of underground pipes, and ultimately discharges, untreated, into surface waters such as rivers, lakes, streams, or wetlands.
In addition to the direct negative impact of the pollutants, runoff discharges often contain large volumes of water, travel at high velocities, and can cause stream levels/depths to rise rapidly. The increased stream flow often results in rapid erosion of stream banks and quickly degrades wildlife species and their habitat. To summarize, here is a list of pollutants and relative impacts associated with stormwater runoff:
- Nutrients (Nitrogen, Phosphorus, etc.) - can cause algal blooms which may have a direct impact on water recreation and fishing (and thus tourism and the economy). Algal blooms are not only physically harmful to the environment; they are also visually degrading and often smell bad.
- Trace Metals - are often bound to sediments in stormwater runoff and may pose a threat to both the environment and human health.
- Sediment/Trash/Debris - as with nutrients, sediment and debris can result in degraded aquatic habitat and health. This impacts water recreation and the environment.
- Oil/Grease - results in degraded aquatic life and habitat and reduces the aesthetic appeal of waterbodies and can be harmful to the environment and human health.
- Salt - results in degraded aquatic life.
- E.Coli and other Bacteria - excess E.Coli and bacteria are harmful to human health and, when elevated, may result in beach closures.
Another (commonly overlooked) negative impact of stormwater runoff is an increased cost to treat drinking water. Most drinking water is taken from natural sources such as lakes and reservoirs and the more polluted these waters are, the more difficult and costly it is to treat the water to meet drinking water standards.
Decreasing Stormwater Pollution at the U
Decreasing stormwater pollution is a responsibility shared by all members of the community. In both our work and private lives, we all must adopt measures to control the pollutants. Some people have jobs that involve direct responsibility for the reduction of stormwater pollution; however, everyone should utilize environmentally sound practices both inside and outside of the workplace, during everyday activities, in order to keep our waters clean. Students, staff, faculty, vendors, and visitors at the University of Michigan should be concerned about stormwater pollution, both on and off campus. Remember, pollution is difficult to handle once it occurs. It is easier and less expensive to control pollution before it happens, rather than to clean it up afterwards.
In the pages that follow, you will discover the many facets of stormwater. You will see how University employees can reduce stormwater pollution throughout daily operations. You will also find the special programs and investigations the University is implementing in an effort to determine and eliminate the sources of stormwater pollution on campus. But, most importantly, you will learn what you can do at home and at work to help reduce the pollution of our surface waters.
We all need to do our part to:
"Keep our Michigan Waters BLUE!"