Minivillage mimics urban sprawl’s impact on water pollution

COSHOCTON, Ohio – Feeling cramped by the busy streets and noise of the city, couples are packing their bags and heading for the country.

The new homes, construction, paved driveways and manicured lawns change the face of the agricultural land and no doubt affect water runoff.

Researchers know this but haven’t been able to do a controlled study. Thanks to a U.S. Environmental Protection Agency grant, researchers with USDA’s Agricultural Research Service now have that chance.

During the multiyear project, water runoff will be scrutinized in miniature residential communities built on four watersheds at the North Appalachian Experimental Watershed in Coshocton, Ohio.

Room to soak. Open farm fields provide plenty of soil and vegetation for rain to soak into before reaching the waterway.

However more people moving to the country means more houses, driveways and roads – and less area for the rain to soak into. This increases the volume and speed of water runoff, risk of flooding, soil erosion and transport of chemicals to waterways.

With this study, researchers will be able to quantify these changes and see exactly when urbanization starts to influence water runoff.

A goal, according to hydraulic engineer James Bonta, is to develop best management practices for builders and home owners – in other words, where to build homes in proportion to the stream channel, the spacing between the houses and ways to use downspouts and tiles.

Another goal of the Coshocton study is to use the information to create a national program to trade runoff credits, just as air pollution credits are now traded.

Slow steps. Scientists will start small, building 3-foot house structures, plowing the soil to simulate construction work, planting lawns, and using pesticides and fertilizers just as homeowners do.

Roofs, driveways and other hard surfaces are called impervious surfaces, and they do not allow rainwater to permeate the soil.

For the first phase of the building, just 5 percent of each watershed will be covered with impervious surface.

Although Bonta doesn’t expect there to be significant changes with so little construction, he stresses that they need to start slow and record data at each step.

As a comparison, Bonta uses an example of plywood in a field: If you put one piece of plywood in the field, water runoff won’t change, but with 20 sheets of plywood, it will certainly change.

“So exactly how many pieces of plywood do you need to start affecting water runoff?” he asked.

Ultimately, impervious surfaces will cover 40 percent of each watershed. Bonta predicts significant water runoff changes at this level.

Advantageous. The advantage of having this experiment at an experimental watershed station is that years of nitty-gritty details are already registered.

Twenty-five years of records on pasture runoff, water quality, nutrients and erosion from agricultural land will help scientists see the changes when the land is “urbanized.”

These records are from the same four watersheds, ranging from 1 acre to 7 acres, that will be used in the mock village.

Put prediction to the test. Bonta already has his predictions about changes that occur with more imperviousness: more volume of water runoff, peak runoff will increase and the time to peak will be sooner.

Researchers will evaluate ways to reduce this runoff, such as building roof gardens to trap rainwater and intermixing natural areas with homes and paved areas, to give water a chance to soak in before reaching waterways.

In the experiments, two housing arrangements will be tested. In one, the houses will be built in a cluster, and in the other, they will be spread over the watershed; both will have the same amount of impervious surface.

Other experiments will test how the proximity between the houses and stream channel affects water runoff.

They will also build tile systems that bypass the stream channel and downspouts that drain into the soil, giving water a chance to infiltrate into the yard before it reaches the stream channel.

Other components of the study include rainfall simulation and computer modeling.

Completion. Researchers plan to start building the village next year but are unsure when it will be complete.

“We’re at the mercy of the weather,” Bonta said. “If there’s a drought, we can’t collect data.”

They also want to see how runoff varies seasonally at each level of urbanization.

(Reporter Kristy Hebert welcomes reader feedback by phone at 1-800-837-3419, ext. 23, or by e-mail at

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