About Stormwater & Runoff



Stormwater is the flow of water that results from precipitation and which occurs immediately following rainfall or as a result of snowmelt.

When a rainfall event occurs, several things can happen to the precipitation. Some of the precipitation infiltrates into the soil surface, some is taken up by plants, and some is evaporated into the atmosphere. Stormwater is the rest of the precipitation that runs off land surfaces and impervious areas.

Runoff & Impervious Surfaces

Stormwater discharges are generated by precipitation and runoff from land, pavements, building rooftops and other surfaces. These hardened surfaces are called ‘impervious surfaces’ and they do not allow rainfall to infiltrate into the soil surface like natural vegetation, so more of the rainfall becomes stormwater runoff. Stormwater runoff accumulates pollutants such as oil and grease, chemicals, nutrients, metals, and bacteria as it travels across land. Heavy precipitation or snowmelt can also cause sewer overflows that may contaminate water sources with untreated human and industrial waste, toxic materials, and other debris.

Reasons for Concern

Stormwater runoff can have a number of impacts. As development and imperviousness increase in an area, the natural capacity of the soil and vegetation to infiltrate and take up rainfall decreases, and more rainfall becomes stormwater runoff. This can produce negative impacts by causing erosion of land areas and stream banks, by causing or increasing flooding, and also by carrying pollutants to surface waters. As Wilson County grows, development increases. When more houses, roads, and businesses are constructed, water has nowhere to go and can cause serious drainage, pollutant, and sanitation problems.

Continued development causes:

  • Increased Imperviousness
  • Increased Runoff
  • Increased Pollutants
  • Impact on Stream Banks
  • Erosion/Sedimentation

Stormwater Runoff

Stormwater runoff may be carried through natural or manmade drainage ways or conveyance systems. In some cases, stormwater runoff leaves a site spread out over a large dispersed area as “sheet flow.” It may also be conveyed through natural ditches, swales and natural drainage features. In most developing and urbanizing areas, stormwater is conveyed through a system of catch basins and pipes commonly referred to as a storm sewer system.

Public Awareness

Public awareness is an important part of stormwater pollutant reduction. Unfortunately, not everyone is currently aware that the decisions they make can have an impact on stormwater pollution. As an example, some people assume that stormwater runoff that enters a storm sewer system is being routed to some type of treatment process before entering our surface waters. In Wilson county, there is no pre-treatment of stormwater. Storm sewer systems are designed simply to capture the stormwater and convey it to the nearest surface water.

View The Culprits (PDF), a resource noting the potential impacts of stormwater runoff.

What You Can Do

There are activities that citizens can be involved with to help control stormwater pollution.

Many of our daily activities have the potential to cause stormwater pollution. Any situation where activities can contribute more pollutants to stormwater runoff is an area that should be considered in attempts to minimize impacts.

The list below is certainly not all-inclusive, but it gives an idea of things citizens can do to help control stormwater pollution:

  • Maintain buffer areas around stream segments to protect stream banks and to provide a mechanism for pollutant removal
  • Minimize impervious areas to reduce runoff
  • Design all new construction to prevent or minimize runoff and stormwater pollution - a major component here is planning upfront in the design process to consider and manage potential stormwater problems
  • Practice “good housekeeping” by keeping areas clean of potentially harmful pollutants - This also may involve changing activities or practices if they have potential impacts
  • Use lawn care practices that protect water quality - minimize the use of fertilizers and pesticides, and when used, do so in a safe manner - When possible incorporate native plant species since they are best adapted to the local growing conditions and tend to be naturally pest-resistant
  • Properly use and store household materials and be aware of and make use of local recycling and collection centers to handle household wastes
  • Remember that any materials that are poured or placed on the ground, streets, driveways, etc. can be picked up and carried by stormwater runoff to our surface waters
  • Report any pollution, illegal dumping, or soil erosion that you see to the appropriate authorities
  • Get involved with local efforts for public education, water quality monitoring, stream cleanup, recycling, etc.