It’s Getting Hot in Here: Why We Monitor Stormwater Temperature

At StormSensor, our goal is to deliver regional-scale stormwater data within a typical monitoring budget. When designing our system, we interviewed many industry experts to help determine what parameters were the most useful to monitor on a continual basis, while also keeping cost in mind. After this intensive research phase, we learned that, outside of flow, water temperature is one of the most valuable parameters to track because it is directly tied to so many other factors related to aquatic health and can quickly and cost effectively be used as a proxy to screen your system. Here, we outline a few advantages of continually tracking stormwater temperature, both at outfalls and upstream within your system.

 

Illicit Discharges and Connections:

A sudden, unexpected change in temperature within your stormwater system can indicate an illicit discharge. Meanwhile, a consistent, yet unexpected temperature can indicate an illicit connection. Some typical illicit discharges/connections have known temperature signatures. For example, human (sanitary) sewage is known to have an average temperature of 60°F, so continually monitoring temperature can not only alert you to the presence of an illicit discharge or connection, but it can also give you some indication as to what the source may be.

Detecting Combined Sewage Flows: Continually monitoring temperature is a known method for cost-effectively detecting combined sewage overflows (CSOs). In a recent study, a team in Australia was able to accurately identify CSO start and stop times nearly 100% of the time using temperature fluctuations as an indicator. Once their method was calibrated, they found that a 0.2-0.4°C change in temperature was nearly as accurate at identifying CSO start and stop times as monitoring actual flow.

Tracking Effects to Receiving Waters: Temperature is one of the most important water quality indicators as it has a direct connection to dissolved oxygen and other biogeochemical processes. As global temperatures warm and our urban and sub-urban regions become increasingly impervious, temperatures of stormwater runoff are rising. In fact, stormwater runoff to Mobile Bay, AL, was tracked at over 120°F in the Summer of 2018.  With stormwater increasingly becoming a source of thermal pollution to our waterways. Continually tracking stormwater effluent temperatures can help determine effects to receiving waters, such as fish kills or algae blooms, in a timely fashion. This knowledge can also be used to prioritize basins for improvements if temperature is found to be a contributing factor to water quality degradation.

Determining Effectiveness of Best Management Practices: It is becoming increasingly frequent for stormwater best management practices (BMPs) to target not only water quantity, but quality as well; and, as previously mentioned, temperature is an important indicator of water quality. Green infrastructure (GI) projects in particular work to regulate the temperature of stormwater runoff. However, much of the monitoring of GI projects is focused on flow. Continually monitoring stormwater temperature, in addition to flow, can help evaluate what sucess these projects are having at mitigating local thermal pollution.

The StormSensor System: The StormSensor system is a powerful combination of hardware and software. Our Scute™ sensors are sold in arrays of 5 to 10 units, each of which measures water level, velocity, and temperature on a continual basis. All measured data are pulled into our web-based Terrapin™ software where it is paired with local weather data. On the StormSensor dashboard, you can view all of your Scute™ sensors in map view, or you can click on each one individually to view time-series data. We are also building machine learning algorithms to learn expected base flows and temperatures, and that means we can flag any unexpected changes as potential illicit discharges or connections. If you’re interested in learning more about how StormSensor could work in your system contact us and we’ll set up a time to talk.

About the author

Suzie Housley

Suzie sees her role in the stormwater world as a “go between” the technical and the general communities. She uses her years of experience to decipher scientific studies and government policies to communicate a practical message.