Webinar Q&A: Climate-smart BMPs: Building resilient stormwater quality measures

In partnership with the Stormwater Equipment Manufacturers Association (SWEMA), SWS presented this webinar on December 4. Climate change is significantly altering precipitation patterns and intensifying extreme weather events, posing a growing threat to stormwater quality. This webinar explored the multifaceted impacts of climate change on stormwater systems, especially BMP design. The speakers, Dr. Mike Trojan, Dr. Elizabeth Fassman-Beck and Dana Stayer, dived into how rising temperatures, changing precipitation patterns, and more frequent and intense storms are affecting runoff volumes, pollutant loads, and the overall health of our waterways.

Below, find answers to common audience questions. The webinar can be viewed on-demand here.

Key topics to be covered include:

• Understanding the relationship between climate change and stormwater quality.
• Examining the specific impacts of climate change on stormwater systems, such as increased flooding, erosion and pollution.
• Exploring innovative strategies for mitigating the negative effects of climate change on stormwater quality with an emphasis on innovative technologies.
• Discussing the importance of sustainable stormwater management practices and the use of BMPs in treatment trains for building resilient communities.

Audience: How much effect does a long dry spell effect the infiltration rates?

Mike Trojan: Several factors affect infiltration rate into soil. If a soil is dry and water is applied to the soil, initial infiltration rates are typically high and decrease over time until reaching steady state. High soil roughness which results in micro depressions, and presence of macropores will influence infiltration rate as there may be areas where infiltration rates are very high initially. High organic matter can impede initial infiltration since it is hydrophobic. Once wet, organic matter typically increases infiltration rate compared to similar soils with lower organic matter content. Sorry if the answer is complicated, but that is the nature of infiltration in soils, and the answer depends on the soil conditions at the location of interest.

Audience: If runoff volume reduction substantially exceeds design, that could that indicate an urban karst situation where runoff is "leaking" from the system? For example around pipe connections or utility corridors which can cause downstream seeps. Will these sites also be flagged for follow up?

MT: This question is intended for Elizabeth, but I’ll add that a situation like this points out the importance of characterizing soil infiltration in the field, including taking the appropriate number of measurements across the area where the SCM will exist. Once steady-state infiltration is achieved, these underground features should not influence the rate of infiltration, but they will affect the flow pathways for infiltrated water.

Audience: Could you please expand little more in depth on the infiltration bank credit mentioned in the 1st presentation?

MT: An infiltration banking credit operates similar to other trading programs, such as with wastewater treatment plants. For example, if a permit requires you to infiltrate 100 cubic feet of runoff, but you can infiltrate 200 cubic feet, you can put the extra 100 cubic feet into a “bank”, which you can either withdraw from and apply at sites where you can’t achieve the necessary volume reduction, or trade (sell) to somebody else. For a system like this to work, there need to be incentives. The incentives can be regulatory (e.g. a permit), or something else, such as reduced costs if you achieve volume beyond a requirement. An example in the case of a homeowner is a reduction in their water bill if they retain water on their property. There also needs to be an accounting mechanism, including an entity tracking all this. I showed an example from the City of Minneapolis, but there are other similar programs.