We often think of thermal pollution in water as a small-scale issue, and that it’s typically associated with large power plants that use surface water as a coolant and then discharge that warmed water back into the environment. However, thermal pollution is defined as any deviation in the natural temperature of a habitat and is becoming a more extensive issue as the climate changes and regions become more heavily urbanized. Sudden temperature changes negatively affect aquatic environments. Smaller and shallower waterbodies, such as streams and lakes, are among the first affected.

Stormwater is a known source of thermal pollution, especially in urban regions. Paved surfaces like roads and parking lots store the sun’s energy. As water flows over these areas, it is warmed and routed, often untreated, into local waters. In events such as summer storms, where surface temperatures are exceptionally high, the result is often thermal shock to local waters. For example, stormwater being discharged directly into Mobile Bay, Alabama, has reached temperatures of 122°F in July, much too high to support aquatic life. To complicate the issue, traditional stormwater retention systems have also been linked to thermal pollution. As water sits and absorbs sunlight, it often becomes much warmer than it would in a more natural system. Discharging this water into local streams and lakes can also cause negative effects such as increased anoxic zones and harm to local fauna.

Urban regions have begun utilizing green infrastructure and bioretention systems to better treat stormwater effluent and mitigate these thermal effects. A study in Virginia determined that bioretention systems can negate thermal pollution by providing a cooler environment and also by slowing the flow rate of release back into the environment. Research is also being done on developing permeable pavements and other building materials that do not trap and store as much heat to be transferred into local waters. More research on the contributions of both stormwater and stormwater treatment systems to thermal pollution of local waters is warranted, especially as we experience a warming climate. StormSensor is up to the challenge! Our sensors track temperature along with flow, allowing you to immediately correlate these factors. We are also developing machine learning algorithms that can aid in tracking flow and temperature changes over time. Contact us if you’re interested in learning more or launching a pilot study in your region.

About the author

Suzie Housely

Talk stormwater with Suzie has over a decade of experience in the Stormwater industry including both government and academic work. She leans on her experience to meaningfully interpret scientific studies and government policies to communicate a practical message. Suzie lives just outside Nashville, TN and gets outside whenever she can to explore nature with her husband and two small children.