SWMM Green Infrastructure for Storm Sewer Overflow

ISEF Category: Environmental Engineering

Subcategory: Water Resources Management  ·  Difficulty: Intermediate  ·  Setup: Home Setup  ·  Time: 1 to 2 Months

The Hook

A single storm can push a neighborhood sewer past its limit. When that happens, dirty water can spill into streets, basements, and rivers. You can test whether green infrastructure, like rain gardens and permeable pavement, lowers that risk. SWMM lets you turn that question into a real model instead of a guess.

What Is It?

This project uses SWMM, the Storm Water Management Model, to simulate how water moves through a neighborhood sewer system. Think of the sewer network like a set of pipes, drains, and storage bins. If rain falls faster than the system can carry it away, water backs up. Combined sewer overflow, or CSO, happens when stormwater and sewage share the same pipes and extra flow spills out during big rain events.

Green infrastructure changes how rain behaves before it reaches the pipes. A rain garden acts like a sponge with plants. Permeable pavement lets water soak through instead of running straight into a drain. In your model, you test how adding these features changes runoff, peak flow, and overflow volume under today’s rain and under climate-projected storms.

Why This Is a Good Topic

This is a strong science fair topic because you can test a real engineering idea with measurable outputs. You do not need a wet lab, but you do need careful modeling, clear assumptions, and good data handling. The topic connects to flooding, water pollution, and climate change, which makes it easy to explain why your results matter. You can also compare retrofit options, which gives your project a clear decision-making angle.

Research Questions

• How does adding rain gardens change combined-sewer-overflow volume in a model neighborhood storm sewer?
• What is the effect of permeable pavement coverage on peak runoff during intense rainfall?
• Does combining rain gardens and permeable pavement reduce overflow more than either retrofit alone?
• To what extent do climate-projected rainfall patterns increase overflow risk in the baseline sewer model?
• Which retrofit mix gives the largest overflow reduction per unit of area converted?
• How does soil infiltration rate change the effectiveness of rain garden retrofits?

Basic Materials

• Computer with internet access and enough storage for model files.
• SWMM software installed on your computer.
• Local GIS data or public storm sewer maps, if available.
• NOAA Atlas 14 rainfall data or local precipitation records.
• Climate projection rainfall summaries from a public source.
• Spreadsheet software for organizing input data and outputs.
• Graph paper or digital notebook for tracking assumptions and scenarios.

Advanced Materials

• Computer with enough memory for repeated SWMM scenario runs.
• SWMM software and model files for scenario comparison.
• GIS software for mapping drainage areas and retrofit placement.
• Local sewer network shapefiles or utility map data.
• High-resolution land cover data for impervious surface estimates.
• NOAA precipitation frequency data and downscaled climate rainfall projections.
• Python or R for batch analysis and statistical comparison.
• ImageJ or GIS tools for measuring retrofit area from maps, if needed.

Software & Tools

• EPA SWMM: Simulates runoff, pipe flow, and overflow for storm sewer systems.
• QGIS: Helps you map drainage areas, land cover, and retrofit locations.
• Excel: Organizes scenario inputs, compares outputs, and makes charts.
• Python: Automates repeated SWMM runs and compares many design scenarios.
• NOAA Climate Data Online: Provides rainfall and climate records for baseline and future comparisons.

Experiment Steps

1. Define the neighborhood boundary and decide which parts of the sewer system your model will include.
2. Gather rainfall data, land cover data, and sewer layout data, then choose a baseline model condition.
3. Identify the one retrofit variable you will change first, such as rain garden area, permeable pavement coverage, or both together.
4. Plan how you will measure success, such as overflow volume, peak flow, runoff delay, or flood duration.
5. Build a set of comparison scenarios, including the original system and several retrofit designs under present-day and projected storms.
6. Design a data analysis plan that compares each scenario with the same metrics and checks whether the effect stays consistent across storms.

Common Pitfalls

• Using a neighborhood boundary that does not match the sewer watershed, which makes the model’s runoff flow paths unrealistic.
• Mixing climate-projected rainfall with current drainage assumptions without labeling scenarios clearly, which makes results hard to compare.
• Treating all green infrastructure as the same, which hides big differences between rain gardens and permeable pavement.
• Ignoring soil infiltration or surface storage assumptions, which can make the retrofit look more effective than it is.
• Comparing scenarios with different storm sizes or durations, which confuses the effect of the retrofit with the effect of the weather.

What Makes This Competitive

A competitive project does more than ask whether green infrastructure works. It tests which retrofit mix works best under different storm types and explains why. Strong projects also compare performance across multiple climate scenarios, not just one. If you add sensitivity analysis, uncertainty checks, or a cost-per-overflow-reduction metric, your project starts to look like real engineering decision support.

Project Variations

• Model a school campus instead of a neighborhood to compare how small watershed shape changes overflow risk.
• Test a green-roof scenario alongside rain gardens and permeable pavement to compare distributed retrofit options.
• Use two different climate projection sources and see how much the choice of future rainfall data changes your conclusions.

Learn More

• EPA SWMM User Manual: Search the EPA website for the official SWMM documentation and example models.
• NOAA Atlas 14: Search NOAA for precipitation frequency estimates to build baseline storm scenarios.
• NOAA Climate Data Online: Search for local rainfall records and historical storm data.
• USGS Water Science School: Read plain-language background on runoff, infiltration, and watersheds.
• MIT OpenCourseWare, Civil and Environmental Engineering: Search for open course materials on hydrology and stormwater systems.
• PubMed: Search review articles on green infrastructure performance and urban stormwater management.