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Keeping the Potomac River Running
By Michael E. Ruane September 29, 2002 Follow @michaelruane

Erik Hagen and Julie Kiang were in search of the water thieves: whoever, or whatever, in these parched times, seemed to be filching precious water from the Potomac River between Point of Rocks and Little Falls.

The two experts weren't sure how, but about 200 million gallons a day appeared to be vanishing between the first spot, south of Frederick, and the second, about 35 miles down river, outside Washington.

On a recent afternoon, armed with a hammer, wrenches and surveying equipment, the two officials of the Interstate Commission on the Potomac River Basin tromped through the woods along the Potomac just below Seneca Creek to check out a hunch.

As they walked into the underbrush, they were suddenly surrounded by the suspects -- silent, gnarled, towering characters. Trees.

It was just as they hypothesized, the pair concluded after taking measurements and checking the level in a freshly sunk well at the river bank. The drought is so bad that the trees' water consumption, which usually affects mainly groundwater, may now be detectable in the flow on the river.

Normally, Hagen said, it wouldn't be much noticed. But these days every drop is missed.

All season, Hagen, deputy director of the basin commission co-op that monitors local water resources, and Kiang, a water resources scientist, have been watching the river, which helps supply water to 3.6 million people in Maryland, Virginia and the District.

And it is they who have been orchestrating the releases of water to the river from two large reservoirs, created decades ago for just such emergencies.

Lately, as conditions have worsened and more and more reservoir water has been required to sustain the proper supply and quality in the Potomac, the task has become increasingly complex and demanding.

"We have to do a lot of forecasting, and a lot of thinking ahead," Hagen said recently. "The river never sleeps."

Among other things, he said, the combined level in the 30 billion-gallon Jennings Randolph reservoir, 200 miles upstream on the Potomac's north branch, and the 3.8 billion-gallon Little Seneca Reservoir, in Montgomery County, has dropped to the lowest point since their creation in the early 1980s.

The combined levels stand at about 65 percent of capacity, Hagen said. The previous low level, during the drought in 1999, was 78 percent, he said.

Joseph K. Hoffman, executive director of the commission, said that when the combined reservoir level drops below 60 percent and stays there for five days, the commission then recommends that the area begin voluntary water use restrictions. Such restrictions could be called for in about two weeks if conditions don't improve, he said.

Hagen said, however, that with the passing of the summer, the consumption of water naturally eases. "We're through the meat, the worst of the drought season," he said. "Now the tree leaves start to come off." With that, the environment's demand for water drops and river flows will start to come up, he said.

In one Potomac tributary, levels are starting to inch up, he said. "It's really amazing."

Even so, the region's water deficit continues to loom, though it was helped by substantial precipitation that fell recently in outlying areas of the Potomac river basin. While the Washington area got a few sprinkles, said Kiang, the water scientist, some areas around the Shenandoah Valley were soaked with more than two inches.

It was enough that a water supply release that was underway at the Jennings Randolph reservoir was halted last week, at least for the moment, Hagen said.

But that still left the question of the missing water, and he and Kiang, who are working on the mystery with the U.S. Geological Survey, took their equipment to the river recently to do some detective work.

Their theory was that the underground aquifer around the river is shallow, sandy and porous, and that trees, which on a hot day can each consume 100 gallons of groundwater, might be indirectly taking water from the river via the aquifer.

Hagen said experts knew that trees could drink up groundwater. "We didn't realize that there'd actually be water coming out of this system to the point where it would be drawing water from the river," he said.

His plan was to compare the level of the river with the adjacent level of the groundwater. A low groundwater level might suggest where the river water was disappearing.

As he and Kiang surveyed the river and dropped an electrode into a shallow well to compare the groundwater, Hagen said: "If the water's lower [in the well], we know that water's coming out of the river and moving into the forest."

When they finished their calculations, they found that the groundwater level was almost a foot lower than the river. "That means that water's moving from the river . . . into the forest, all up and down, probably both sides of the river."

"You start looking at all these trees," Hagen said, indicating the quiet suspects bent toward the Potomac, "and you can see why there's this big gradient."

The real culprit, though, arched overhead: It was clear and blue and held not a single cloud.

Scientist Julie Kiang of the Interstate Commission on the Potomac River Basin checks the water level inside a pipe along the river, which helps supply water to 3.6 million people.Erik Hagen and Julie Kiang monitor the river's water levels. The two control the releases of water to the river from two large reservoirs.