Runoff and Groundwater Recharge
Editors Note: Guest post feature by Sarthark Pal Mahajan and Aadhavan Muralidharan, rising 11th-grade students in the Global Ecology Program at Poolesville High School.
Reducing Urban Runoff and Protecting Groundwater
Urban runoff is a growing problem caused by the spread of pavement and other impermeable surfaces in suburban areas. Water that should soak into the ground instead rushes into storm drains, reducing groundwater recharge and polluting waterways. In fact, the average suburban area is 75–100% covered by surfaces that don’t absorb water. This results in 55% of rainfall becoming runoff, compared to only 10% in natural ground cover areas.
In Montgomery County, Maryland rapid suburban development has replaced forests and fields with roads, parking lots, and buildings, drastically reducing the amount of rainwater that can soak into the ground. According to the Montgomery County Department of Environmental Protection, up to 60% of rainfall becomes runoff in urbanized areas. This runoff carries pollutants like oil, fertilizers, and litter into local waterways such as Rock Creek and the Potomac River, threatening wildlife and drinking water. These rivers are part of the Chesapeake Bay Watershed, one of the largest and most vital estuaries in the United States. The bay supports thousands of species and supplies economic and recreational value to the region, meaning local pollution has far-reaching environmental, economic, and societal impacts. By implementing green infrastructure (such as rain gardens, green roofs, and permeable pavements) we can reduce runoff, improve groundwater recharge, and protect local ecosystems.
A rain garden in Silver Spring, Maryland. Image from Maryland Dept of Environmental Protection.
By the Numbers
4% is how much groundwater recharge decreases due to a 12% increase in urban area.
60% of rainfall becomes runoff in highly developed Montgomery County neighborhoods.
1 inch of rainfall on a 1,000 sq. ft roof generates over 600 gallons of runoff—enough to fill 10 bathtubs.
350 green streets and rain gardens that are actively reducing runoff in Montgomery County.
Five Ways You Can Help
Responsible lawn care. You can do this by minimizing your use of chemical fertilizers and pesticides. Only apply fertilizer that is needed and don’t spread it near surfaces such as sidewalks and driveways, where it is prone to washing into storm drains. Store fertilizers and other chemicals at least 100 feet away from wells, drains, and water sources.
Plant native vegetation. Native plants help conserve water, reduce erosion, and they even help support wildlife. Native plants are suited for local conditions which can mean they don’t need as much maintenance or fertilizer. They are helpful in a variety ways to the environment.
Help install rain gardens. Rain gardens capture and filter runoff from hard surfaces. They help reduce pollution and recharge groundwater. Here is an in-depth guide that shows how you can build one.
Pick up after pets and dispose of waste properly. Pet waste has harmful bacteria which can pollute waterways. Carry pet waste bags when you walk your pet and make sure to dispose of the waste in a trash can, don’t leave the waste outside or in storm drains.
Advocate for change. Support local policies and programs that support water resources and other environmental causes. Testify to the County Council on issues relevant to water runoff and write to politicians advocating for green infrastructure and stricter pollution regulation.
Infographic from NEEF.