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Center for Advancing Research in Transportation Emissions, Energy, and Health (CARTEEH)

A USDOT University Transportation Center

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Reduction of Runoff Velocity

There are various structures and design techniques that can lower the runoff velocity to prevent erosion and encourage sedimentation.1 Since runoff can carry a lot of sediment and other pollutants, urban areas can install different devices to allow runoff to flow at slower rates so that these materials can be absorbed into the soil, a process known as infiltration.2 Some of these devices may include concrete structures or porous barriers.3 Drop structures are concrete designs that can be used to stabilize waterways, serve as outlets for water flow, or act as sediment traps. Riprap is an example of a porous barrier that consists of a layer of stones or cobbles lining a channel for the purpose of increasing surface roughness and slowing runoff velocity.4 In addition, grassed waterways can reduce runoff velocity and remove excess runoff by absorbing sediments and other substances.5,6 This solution can divert water while reducing both soil erosion and flooding.

Considering this strategy will help achieve the goal of the following objectives

  • Less Contamination
  • Less Emissions
  • Less Traffic Noise
  • Connectivity and Inclusion
  • Healthy Destinations
  • Less Traffic Violence
  • Active Transportation
  • Green Space

Transportation lifecycle phases

This strategy is associated with the following transportation lifecycle phases:

  • Construction
  • End of Life
  • Maintenance
  • Material Selection
  • Operations
  • Policy and Planning
  • Project Development

Who's involved

  • Drainage engineers
  • MPOs
  • Private developers
  • Transit agencies

There are various structures and design techniques that can lower the runoff velocity to prevent erosion and encourage sedimentation.1 Since runoff can carry a lot of sediment and other pollutants, urban areas can install different devices to allow runoff to flow at slower rates so that these materials can be absorbed into the soil, a process known as infiltration.2

Some of these devices may include concrete structures or porous barriers.3 Drop structures are concrete designs that can be used to stabilize waterways, serve as outlets for water flow, or act as sediment traps. Riprap is an example of a porous barrier that consists of a layer of stones or cobbles lining a channel for the purpose of increasing surface roughness and slowing runoff velocity.4

In addition, grassed waterways can reduce runoff velocity and remove excess runoff by absorbing sediments and other substances.5,6 This solution can divert water while reducing both soil erosion and flooding.

How it Helps

Since climate change is expected to increase the frequency of severe storm events, heavy precipitation can increase runoff velocity and lead to erosion issues and prevent nutrients from absorbing into the soil.7 Erosion prevention practices and other efforts to decrease runoff velocity can promote soil infiltration and lead to less polluted runoff entering the storm drain system.

Implementing

Flooding Potential:

Although reducing runoff velocity has several positive impacts, including preventing soil erosion and removing polluted runoff, it may not be applicable in certain areas where higher velocities are required to maintain drainage rates.1 Some highways and roadside surfaces may need to be drained quickly to prevent flooding and other roadway safety hazards. Therefore, planners and drainage engineers should consider these factors when determining where to implement devices to slow runoff velocity.

Design Characteristics:

Depending on the surrounding environment, engineers and other experts will have to choose which structures and designs to reduce runoff velocity are best suited for a particular area. Drop structures, ripraps, grassed waterways, and other strategies each have advantages and disadvantages for certain situations that should be carefully analyzed prior to construction.

Examples

1) Drop Structure Design

There are many examples of drop structure, riprap, and other possible designs available for drainage engineers and planners to utilize when determining how to construct one of these structures. Many of these publications or reference manuals provide comparisons between the various subtypes of structures, details regarding the necessary supplies, and other design considerations.

https://www.hec.usace.army.mil/confluence/rasdocs/ras1dtechref/latest/modeling-gated-spillways-weirs-and-drop-structures/drop-structures

1. Maestri, B., et al. Managing Pollution from Highway Storm Water Runoff. Transportation Research Record 1166. https://onlinepubs.trb.org/Onlinepubs/trr/1988/1166/1166-003.pdf
2. Water Science School. (2018). Runoff: Surface and Overland Water Runoff. USGS. https://www.usgs.gov/special-topics/water-science-school/science/runoff-surface-and-overland-water-runoffWater Science School. (2018). Runoff: Surface and Overland Water Runoff. USGS. https://www.usgs.gov/special-topics/water-science-school/science/runoff-surface-and-overland-water-runoff
3. World Environment Library. Sustainable Management of Soil Resources in the Humid Tropics: Structures to reduce runoff velocity. http://www.nzdl.org/cgi-bin/library?e=d-00000-00---off-0envl--00-0----0-10-0---0---0direct-10---4-------0-1l--11-en-50---20-about---00-0-1-00-0--4----0-0-11-10-0utfZz-8-10&cl=CL1.6&d=HASH01f1aaf596c48d8344b21037.10.3.3>=1
4. Minnesota Pollution Control Agency. (2023). Minnesota Stormwater Manual: Erosion prevention practices - Riprap. https://stormwater.pca.state.mn.us/index.php?title=Erosion_prevention_practices_-_Riprap
5. Soil Management. Grassed Waterways: Construction and Maintenance. https://www.soilmanagementindia.com/soil-erosion/grassed-waterways/grassed-waterways-construction-and-maintenance-soil-management/15235
6. Fiener, P., et al. (2003). Effectiveness of Grassed Waterways in Reducing Runoff and Sediment Delivery from Agricultural Watersheds. Journal of Environmental Quality, 323, 927-936. https://doi.org/10.2134/jeq2003.9270
7. Janowiak, M., et al. (2016). Adaptation Resources for Agriculture: Responding to Climate Variability and Change in the Midwest and Northeast. USDA Climate Change Resource Center. https://www.fs.usda.gov/ccrc/approach/reduce-peak-flow-runoff-velocity-and-soil-erosion