As new homes and other development gobble up more and more land, a new study shows a direct link between land use and quality and quantity of water supply.
According to a recent report by three environmental, nonprofit organizations, suburban sprawl is shaking up the way water moves from rain clouds to rivers and streams in ways that have yet to be fully explained.
The three groups — American Rivers, the Natural Resources Defense Council and Smart Growth America — found that sprawl exacerbates drought, erodes streams and hurts water quality.
The results stunned the researchers, according to Betsy Otto, the senior director for watershed programs for American Rivers and a co-author of the report.
"There's something very big going on," she said.
The study provides reinforcement for many Montgomery County landuse policies, including the designation of Potomac as a low-density buffer for the Potomac River, the preservation of open space in the agricultural preserve through Legacy Open Space.
“We may not be able to do too much about the weather in the short-term, but by using our land resources more wisely, we can protect our water supplies for the long term,” said Neil Fitzpatrick, a Potomac resident and executive director of the Audubon Naturalist Society in Chevy Chase.
“By applying smart growth principles, we can not only protect our critical water resources, but also create better places for people to live.”
When rain or snow falls in an undeveloped area, water percolates into the ground, while some of it runs off into streams and rivers. The water that seeps into the ground, known as the ground water, replenishes underground aquifers over a period that can be as short as less than one day, or as long as over a million years, depending on the type of soil. Those underground aquifers will eventually empty into streams and rivers, which constitute surface water.
Streams and rivers get about half their water flow from groundwater, so failing to replenish groundwater supplies results in failing wells and reduced water supply in rivers as well.
The Metropolitan Council of Governments (COG) monitors ground water levels around the region, and as of the end of August, 2002, 12 of the 18 groundwater observation wells in the COG region were below normal, including three of the four observation points in Montgomery County.
When land is blanketed with roads, parking lots and shopping plazas, rain and snow are immediately drained to streams, cutting off the underground aquifers from their main water source, Otto said. This means that there is less water for plants to suck up through their roots. It also interferes with the complex water cycle, according to Otto.
"We're changing the timing of when the water comes into the stream. And how [it enters the stream]," she said.
"If you pave over a site, water is not going to go into the ground, it's going to run off," said Noel Kaplan of the Department of Planning and Zoning's Planning Division in Fairfax County, Va. "The water is going to run off into the surface water system."
The water also picks up pollutants as it runs over roads and parking lots. When it is allowed to percolate into the ground, the soil acts like a filter, blocking the pollutants and sending relatively clean water to replenish the underground water tables. When the water is siphoned off straight to the surface water, those pollutants are dumped into the stream.
"It's sort of like a pump of pollutants that goes into our water bodies," said Otto.
Water that runs off a parking lot can also be up to 15 degrees warmer than water that seeps through the ground. Aquatic life forms are affected. Algae bloom in streams, which can choke fish.
Otto mentioned smart growth development and better storm-water management as possible solutions. The idea, she said, is to treat storm water as a resource rather than as a waste product.
"The ideal storm-water management approach is designed to infiltrate and to also provide habitat for birds and insects and wildlife," she said.
How Much Is Enough?
How much water needs to flow in the Potomac River to maintain a healthy environment for fish and wildlife that depend on it?
Until recently, state and county agencies worked with the assumption that 100 million gallons a day was the magic number, but that number was not based on any scientific research. Now the Maryland Department of Natural Resources has embarked on a study, assisted by the Department of Environmental Protection in Montgomery County, to determine what amount of water is really needed.
In recent months, water has been released from upstream reservoirs just to maintain the 100 million gallon level.
“Absent careful water-use planning, the ecosystem functions of the Potomac River could be seriously impaired in the coming decades,” wrote Ronald Lambertson of the U.S. Fish and Wildlife Service in 1999, seeking to bring some science to minimum water flows. “The service does not agree that 100 million gallons per day minimum flow-by is adequate to protect the Potomac River ecosystem.”
The ongoing studies will determine how much water is needed both to provide adequate drinking water and protecting the natural and biological resources of the Potomac River, said Keith Van Ness, biologist with the county Department of Environmental Protection. Van Ness and other county water monitors will provide some of the labor for the state evaluation.
“This gives us an opportunity to collect data and understand the impacts of low flow habitat, and to understand what impacts those low conditions have on aquatic abundance and diversity,” said Neil Fitzpatrick of the Audubon Naturalist Society. “In our view, we need better, more recent, more scientific data to understand the impact on the ecosystem of the river under low flow conditions.”
—Ken Moore