While not originally considered as a thermal pollution treatment mechanism, stormwater BMPs do have an impact on runoff temperature. A description of stormwater BMPs common to North Carolina and background on their potential effect on runoff temperature can be found below.

Bioretention Area

Overview

• Bioretention areas function by collecting stormwater runoff and allowing the runoff to infiltrate through soil
• These BMPs often contain some type of underdrain network and are designed to only temporarily retain water
• For more information on bioretention area background and design, visit these BAE publications:
  • Designing Rain Gardens
  • Bioretention Performance, Design, Construction, and Maintenance

Factors Relevant to Runoff Temperature

• Decreased daily fluctuations with greater soil depth
• Shading from vegetation
• Underdrain depth
• Outlet configuration
• Soil media properties

Stormwater Wetland

Overview

• Stormwater wetlands are constructed wetland systems containing regions of deep pools, shallow water, and shallow land
• Stormwater wetlands are vegetated with a variety of plants suited to the water depth and climate where they will be planted
• For more information on stormwater wetland background and design visit this BAE publication:
• Designing Stormwater Wetlands for Small Watersheds

Factors Relevant to Runoff Temperature

• Shading from vegetation
• Exposed surface area
• Water depth
• Inlet and outlet structure design

Wet Pond

Overview

• Wet ponds are open pond systems with a water depth between 4 and 10 feet.
• This BMP is often installed near shopping centers or other areas with larger watersheds
• Wet ponds differ from stormwater wetlands in that they have a relatively uniform depth and contain less vegetation
• For more information on general BMP designs, including wet ponds, visit this BAE publications:
• Urban Stormwater Structural Best Management Practices

Factors Relevant to Runoff Temperature

• Exposed surface area
• Water depth
• Inlet and outlet structure design