Rain Garden vs. Lawn Runoff Study

ISEF Category: Earth and Environmental Sciences

Subcategory: Environmental Effects on Ecosystems  ·  Difficulty: Intermediate  ·  Setup: Home Setup  ·  Time: 1 to 2 Months

The Hook

A patch of garden can act like a sponge, while lawn can behave more like a slow leak. That difference changes how much water stays in the ground and how much rushes away after rain. Your backyard can reveal that in numbers. You can measure it with simple sensors and a bucket.

What Is It?

A rain garden is a planted area built to catch water and let it soak into the soil. A lawn is usually flatter, more compacted, and less likely to hold water for long. Think of the soil like a kitchen sponge. A loose, healthy soil soaks up water fast. A packed soil acts more like a plastic tray.

Your project compares how much water each surface absorbs, how much runs off, and whether the water that leaves the area carries less nitrate. Nitrate is a common nutrient in fertilizer. Too much of it can wash into streams and feed algae growth. You are not just asking which area gets wetter. You are asking which surface keeps water and dissolved nutrients in place better.

Why This Is a Good Topic

This is a strong science fair topic because you can measure real environmental change with simple tools and clear numbers. You can test water movement, runoff, and nutrient retention without a university lab. The topic connects to stormwater pollution, flood control, and lawn management, so your results matter beyond your yard. You can also learn how to design controls, compare paired sites, and turn messy outdoor data into a clean analysis.

Research Questions

• How does soil moisture recovery after rainfall differ between a rain garden and a nearby lawn?
• What is the effect of surface type on runoff volume collected after the same rainfall event?
• Does the rain garden retain more nitrate than the lawn runoff after storm events?
• To what extent does soil compaction explain differences in infiltration between the two sites?
• Which site shows the fastest drop in soil moisture after rain ends?
• How does plant cover change runoff reduction across repeated rainfall events?
• What is the effect of antecedent dry days on runoff from the rain garden and the lawn?

Basic Materials

• Soil-moisture sensors with data logging or readout capability.
• Bucket or container runoff collector with marked volume.
• Flexible tubing or gutter-style channel to direct runoff into the collector.
• Cheap nitrate test strips or colorimetric nitrate kit.
• Measuring tape or ruler.
• Digital kitchen scale with 0.1 g accuracy.
• Rain gauge or access to local rainfall records.
• Notebook or spreadsheet for field notes.
• Flags or stakes to mark sampling spots.
• Camera or phone for site photos.

Advanced Materials

• Automated soil-moisture probes with multiple depths.
• Portable flow meter or tipping-bucket runoff setup.
• Spectrophotometer or colorimeter for nitrate analysis.
• Filtered sample bottles and labeled storage containers.
• Replicate soil cores for bulk density and compaction estimates.
• Infiltration ring or double-ring infiltrometer.
• Data logger with timestamped sensor output.
• Reference standards for nitrate calibration.
• GIS or mapping software for site layout and drainage area estimates.
• Weather station or high-resolution rainfall dataset.

Software & Tools

• Google Sheets: Organizes field measurements, graphs runoff trends, and compares paired sites.
• ImageJ: Helps you extract color values from nitrate test strips or sample images.
• Python: Supports cleaning sensor data, making plots, and running basic statistics.
• RStudio: Lets you test differences between sites and model rainfall effects.
• NOAA Climate Data Online: Provides local rainfall records for matching your observations to storm events.

Experiment Steps

1. Define the two sites you will compare and make sure they receive similar rainfall exposure.
2. Choose your response variables, such as runoff volume, soil moisture change, and nitrate level.
3. Map the drainage area, slope, and plant cover so you can explain differences later.
4. Plan a repeatable sampling schedule that captures multiple rain events and dry periods.
5. Build your data table and decide how you will normalize results for rainfall size and site area.
6. Set controls that separate real infiltration effects from soil compaction, shade, or watering differences.

Common Pitfalls

• Placing the runoff collector in a spot where splash, overflow, or wind changes the collected volume.
• Comparing sites with different roof, driveway, or slope inputs, which makes the runoff data unfair.
• Reading nitrate strips under changing sunlight, which shifts the color match and weakens repeatability.
• Using only one storm event, which hides how soil moisture and infiltration change over time.
• Ignoring soil compaction or mulch depth, which makes it hard to tell whether plants or soil structure caused the effect.

What Makes This Competitive

A stronger project goes beyond one simple before-and-after comparison. You can build a paired design, match storms by rainfall intensity, and normalize runoff by site area. You can also test whether nitrate retention tracks soil moisture, compaction, or plant cover. If you add repeat measurements across many storms, your project starts to answer a real environmental question, not just describe one backyard.

Project Variations

• Compare a rain garden, a lawn, and a bare-soil control to separate plant cover from soil effects.
• Test native plants versus ornamental plants inside rain garden plots to see which holds back more runoff and nitrate.
• Use smartphone image analysis instead of strip reading to compare nitrate color changes across samples.

Learn More

• USGS Water Science School: Read plain-language pages on infiltration, runoff, and groundwater at the U.S. Geological Survey site.
• NOAA National Weather Service: Find local rainfall records and storm data through NOAA climate and weather resources.
• USDA NRCS Soil Health Portal: Learn how soil structure, compaction, and organic matter affect water movement on USDA pages.
• NIH PubMed: Search for review articles on stormwater runoff, rain gardens, and nutrient retention.
• NASA Earthdata: Explore land and water data tools that help you connect local observations to broader environmental patterns.