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Scientists and environmental activists are increasingly alarmed by the waning amount of water running through North Carolina's streams and rivers. The deficits aren't smalland depending on climate, growth, and water use, they could affect the general public. In fact, according to a recent study by the U.S. Geological Survey, water measured in low-flow periods dropped by nearly a fifth between 1998 and 2011.

The net effect of the 18 percent decreasecaused by such factors as increased development and water withdrawals, as well as climate changeis that less water is available for drinking and for diluting effluents and other pollutants discharged into streams.

Chris Goudreau, a biologist with the state Wildlife Resources Commission, says North Carolina's rapid growth should make the state's water quality and quantity a priority.

But state and local governments in North Carolina have "very limited" power over water withdrawals, says Richard Whisnant, a professor of public law and policy at UNC-Chapel Hill. In fact, towns such as Rocky Mount have run out or nearly run out of water during droughts.

By comparison, people who want to divert water from a river in California have to, among other requirements, file an application with the state, pay fees, show that their project would not harm natural resources, and demonstrate that the project is in the public interest.

Environmentalists say the state should toughen the requirements on permits for withdrawals to reflect the lower water flow. But a state government dedicated to dismantling regulations shows no signs of taking that step.

"The stream flow is really important to permits and the health of the streams, and basically the regulatory system hasn't really kept up with the science," says Bill Holman, state director of the nonprofit Conservation Fund and former secretary of the N.C. Department of Environment and Natural Resources. "The 7Q10 is barely enough water to keep the stream system alive."

The measurement called 7Q10 is used as a standard in discussions of water availability. It reflects a disastrous situation: "The lowest stream flow for seven consecutive days that would be expected to occur once in ten years," according to the EPA.

The landmark study conducted by USGS hydrologist Curtis Weaver looked at 7Q10 data from gauges in sixty-three streams across the state between 1998 and 2011, a period when the state experienced extremes in weather.

"We've had several off and on drought periods since the late nineties," Weaver says. "One of the questions we wanted to pose was, has the 7Q10 discharge across the state decreased? Do we have evidence yes or no? [The study] suggest it's yes."

The state Division of Water Resources also found downward trends in a 2014 study of three North Carolina river basins.

Even though the last full year Weaver studied was 2011, statewide levels of rain and heat are unlikely to have appreciably changed the stream-flow levels since then, says Rebecca Ward, extension climatologist at the State Climate Office. Droughts in 2002 and 2007-08 could have affected the short-term result but wouldn't affect the trend over time.

"What we can say with confidence is that long and severe droughts are a part of our history, and it's likely we will see such climate events again," she says.

Lowered stream flows can have far-reaching effects that might not immediately spring to mind, says Peter Raabe, state conservation director for the nonprofit American Rivers. For instance, low-flow conditions in streams can make life tough for benthic macroinvertebrates, or "benthos," small creatures that live on the bottom of streams, eating algae and in turn being eaten by fish. The presence or absence of these creatures also serves as an indicator of water quality.

Municipal and industrial use of North Carolina's rivers can lead to reduced water flowpractices as small as watering your lawn and as large as using rivers to cool power plants.

Hydrologists have measured stream flow for decades, in many cases to determine the relationship of water quantity and quality. And state legislators grew concerned enough about the issue in 2010 to pass a law directing environmental regulators to create plans to find the stream flow for each of the state's seventeen river basins to protect their ecological integrity. (That means its ability to support a climate of biodiversity, to recover from disruption, and to "continue to provide the natural goods and services that normally accrue from the system.")

The law's passage led to the creation of the Ecological Flows Science Advisory Board, which met for three years and issued a report that proposed possible approaches to assessing the basins' viability. They included measuring critical low flow and/or "biological response"in other words, changes wrought by stream volume.

The response from the McCrory administration's environmental agency: "DENR does not plan to implement the biological response or critical low-flow recommendations at this time, pending further evaluation."

But officials at several levels continue to deal with the lessening flow.

Tom Fransen, water planning chief at the Division of Water Resources, says the city of Raleigh's 2014 objections to the advisory board's recommendations as potentially too restrictive meant new rules had to be approved or state law had to be modified. That didn't happen in the recently concluded legislative session.

Ed Buchan, Raleigh's environmental coordinator, says citizens have done well in reducing water usage since the drought of 2007–08. But that doesn't mean the city can ignore the possibility of the reduction in Falls Lake's "safe yield" or the consistent water supply from the lake during a drought.

"We would be concerned about a trend of declining average flows in the Neuse River basin (especially in the Upper Neuse Basin)," Buchan writes in an email. "In reviewing 80+ years of inflow data into Falls Lake (or more properlythe Falls Lake area since it wasn't constructed until 1983), it appears there has been a slight decline in average inflows during this time period."

A new EPA tool predicts that increased rainfall levels may be on the way, Raleigh officials say. Writes Buchan: "It is a bit of a mixed bag when it comes to water resources in the Neuse River Basin, but as water providers to over 550,000 residents, we tend to be pretty conservative and have integrated the declining inflow trend into our ongoing planning efforts."

"The biggest concern is that when our streams have reduced flow, that's our drinking water," says Raabe. "How do we manage that water so that we meet all our needs? The environmental part of it is, these ecosystems are designed to have a certain amount of water in them. Just like it's a drinking water source for us, it's drinking water [and habitat] for all those animals. When that changes, it could be a really delicate change."

This article appeared in print with the headline "Low Flow"