Precipitation data throughout the region indicates that larger storm events are occurring more frequently. The 10-year storm event, which theoretically has a 10% chance of occurring in any given year, is occurring more than once every 10 years. Shorter, more intense rain events also occur which rapidly overwhelm existing infrastructure. This excess runoff flows overland, flooding businesses, homeowners, and streets; making them inaccessible for significant durations of time.

There is no single solution to managing increased rainfall and keeping priority roads and buildings accessible. Options include expanding underground storm sewers or enhancing above-ground stormwater management. Both require careful planning and investment.

A stormwater master plan can assist communities in cost-effectively planning for regional or local improvements, including green infrastructure, conventional detention facilities and/or storm sewer conveyance improvements. A multi-dimensional stormwater model and master plan can analyze a community's current infrastructure system and identify priority areas, allowing for appropriate planning and budgeting.

Understanding 2D vs. 3D Stormwater Modeling

Stormwater modeling takes the municipality’s existing storm infrastructure and calibrates the program to what one would see for a typical 10-year, 50-year, or 100-year storm event. The modeling utilizes traditional 2D modeling efforts as well as 3D modeling functions. The difference between the modeling is shown in the table below. 2D modeling efforts are utilized to calibrate the model. 3D modeling functions allow for the visualization of the spread of overland flow when the storm sewer infrastructure no longer has the capacity to maintain the runoff within the pipes underground. This is done by utilizing terrain data that captures the slope on the ground and any open channel flow ways.

2D Stormwater Modeling

Utilize pipe and manhole characteristics in calculations

Determine when pipe is at capacity and when the manhole will over-top and contribute to overland flow
Typical profile view of system

3D Stormwater Modeling

Utilize pipe, manhole, and terrain slope in calculations

Determine what depths the overtopping at the manholes will be
Spread of stormwater across a terrain

The stormwater model allows for different storm scenarios to be completed with instant visual results of flooding extents. Storm scenarios can include anticipated increases in storm events or larger than 100-year events.

The instant visualization of the depths and spread of the runoff assists in the prioritization of improvement areas. Other factors such as primary access routes for emergency vehicles, proximity to lift stations, and number of flooded structures also contribute to what areas are considered high priority and need improvements.

Stormwater model and master plan can also perform high-level alternatives on the types of improvements that would have the greatest impact on the flooding extents and depths. The actual size of the pipe to mitigate the overland flooding is sometimes not feasible to fit underground along with the other existing utilities. Sometimes a combination of storm sewer infrastructure upsizing and above ground storage is utilized to meet the goals of the municipality.

Utilizing the anticipated size of the improvements needed based on the high-level alternatives can assist with budgets and planning. This allows for more specific budgetary line items for the yearly budget and how many projects can be completed each year.

A Picture Speaks 1,000 Words

The 3D modeling methods of a stormwater plan allow a significant amount of information to be presented visually. Visualization allows for clear and concise information to be presented to the community. Project storyboards can help convey to the community certain aspects of a project such as timeline, but also visually present the improvements to the flooding extents and depths before and after the implementation of the project. Videos, in addition to photos, showing simulated flooding over time are great tools to convey technical information to elected officials and residents.

With storm events becoming more frequent and intense, municipalities must take proactive steps to reduce flooding and keep roads accessible. Stormwater master plans help identify problem areas and guide decisions on infrastructure improvements, whether through larger underground pipes or above-ground storage solutions.

Using advanced 3D modeling, communities can better visualize flood risks, prioritize critical areas, and explore cost-effective solutions. R/M can help municipalities develop smart, data-driven flood mitigation strategies.

R/M Can Help

About the Author

KATELYN VANDENBERG, P.E.
Project Engineer

Katelyn’s background includes construction review and the study of wetlands, soil, and ecology. She received her Bachelor of Science in Environmental Engineering with a Minor in Ecology from Michigan Technological University, where she also served as the President of the Society of Women Engineers.

Innovative 2D/3D Flood Mitigation for a Resilient Future