Where has Montana’s water gone?

An old compact may not be enough to keep the Tongue River from running dry

  • Precision irrigation near Gillette, Wyoming, in the Yellowstone River Basin, where new, more efficient methods lead to less water for Montana in the rivers downstream.

    Joel Sartore, National Geographic, Getty Images

The first thing Roger Muggli learned about irrigation was that water runs downhill.  His grandfather managed an irrigation district near Miles City, Mont., and together they tended the ditch. From the fields they would trace the water's passage to an oxbow on the Tongue River. Now, Muggli, 62, works the same job alone, patching pipes, scouring the canal and cutting debris from the banks.  When the soil thaws and alfalfa sprouts, he opens the headgates, and water rushes into the main ditch. There, it meets smaller ditches and seeps into the furrows like blood across a weathered palm.

Muggli has seen dry years, but never like 2004 and 2006, when his irrigation district had only half its water right fulfilled. A normal season yields 100 barley bushels per acre, but he threshed no more than 45. Where the Tongue River crosses into the state from Wyoming, a reservoir that often overflowed never even filled. "It was a logistical nightmare," says Muggli. "People don't like you turning off their water."

Meanwhile, in Wyoming, water commissioners fielded calls from senior water-rights owners who weren't seeing their share. In response, they cranked headgates closed, shutting off newer rights first in accordance with basic water law. In one drainage in 2006, the only user left operating had rights dating to 1890. But along the main stem of the Tongue, a few junior water rights holders operated all season. There was nobody downstream to complain, but Montanans.

"First in time, first in right" guides how water is divvied up within states but doesn't always apply across borders. Wyoming and Montana instead rely on the 1950 Yellowstone River Compact, which governs how the states share four Yellowstone tributaries -- the Powder, Tongue, Bighorn and Clarks Fork -- in times of scarcity. It guarantees both states continued access to any rights issued before 1950. To satisfy later rights, the states are promised fractions of each river's remaining flow.

The Compact's drafters suspected that the Yellowstone's tributaries were already fully allocated in 1950. They hoped the agreement would satisfy Montana's older water rights in dry years, even if Wyoming kept issuing new ones. But post-1950 rights were not Montana's only trouble. Over time, water use changed: Irrigators swapped ditches for center-pivot sprinklers, and energy companies drilled the first coalbed methane wells, pumping vast amounts of water from deep aquifers.

For years, water was plentiful, so Montana didn't worry. Only when the state's senior water users received less than ever before did they begin to wonder where their water had gone. In both 2004 and 2006, Montana asked Wyoming to release water from storage to satisfy the pre-1950 rights it thought were guaranteed. Wyoming refused. In 2007, Montana sued Wyoming for violating the Yellowstone River Compact. The case landed in the Supreme Court this January.

Montana attorneys can't say for sure where their state's water went those years. But they suggested four possibilities that made Wyoming liable: groundwater extraction; excessive water storage; new uses like coalbed methane; and advances in irrigation technology that allowed farmers to consume more of their water right than before. (Wyoming's explanation was simpler: drought.) The special master -- a water-law expert appointed to review the case and advise the Supreme Court -- sided with Montana on the first three claims, but with Wyoming on the fourth. Montana objected on that last count, so the question was put to the High Court itself, which on May 2 decided in Wyoming's favor. The decision allows Wyoming farmers to switch to advanced irrigation technology even if it means consuming water that otherwise would flow back to the river for another user.

Irrigation efficiency has its merits, but it's created unexpected downstream shortfalls that Montana farmers may now be forced to live with. Unlike many similar agreements in the West, the Yellowstone Compact never quantified the minimum amount of water Wyoming must deliver to Montana each year.  And it was written at a time when gravity, not pumps, governed water use. "People don't always anticipate what's going to happen over time," says Barbara Cosens, professor of law at the University of Idaho. "The older compacts did not account for groundwater development. Nor did they anticipate that irrigation efficiency works very different in practice than in theory."

When an irrigator applies water to a field, some of it transpires through the plants, and some evaporates. The rest -- the return flow -- seeps across the floodplain or through the aquifer to recharge the river's loss.  One farmer's backwash becomes another's water source.

But from an upstream farmer's perspective, water that evaporates, percolates or runs back to the river is a loss -- one that modern technology is designed to curtail. In 1997, when the Farm Bill began providing financial incentives for efficiency upgrades, Tongue River farmers replaced flood-irrigation systems with center-pivot sprinklers, which promised higher yields and water savings. Sprinklers applied water evenly, and crops flourished. In theory, irrigators were conserving water: The plants absorbed more of what was applied, so they didn't need to take as much from the river.

In practice, it wasn't so simple. Flood a field with 100 units of water, the plant takes 40. Sprinkle it with 80, the plant takes 60. More water stays in the river initially, but more is also consumed in the field. And when less returns to the river, in the long run, the basin sees a loss.

Both Montana and Wyoming know how much water irrigators take, but not how much crops are consuming or what volume returns to the river. Agencies, in turn, regulate the quantity of water a user diverts from a source, not the amount consumed. "If water rights were based on water depleted rather than water applied, then there wouldn't be this problem," says Frank Ward, professor of water resource economics at New Mexico State University. "But depletion is really tricky to measure."

Sprinklers have grown popular in both Montana and Wyoming. But the federal subsidies that lubricated the switch were given with different conditions. In Montana, farmers must agree to return saved water to its source or take less from the river. In Wyoming, if farmers have water left, they can use it on a field they may have neglected during drier years, leaving less for downstream users.

"A general rule in water law is that you can't force someone to not improve efficiency," says Cosens. "If they do a better job on the acres they irrigate, you can't do anything about it." That's been true within states. But now the Supreme Court has stretched this rule across borders; if Wyoming farmers have a right to a certain amount of water, who is to tell them they can't consume it all?

Montana attorneys are at least relieved to have won on coalbed methane, which poses a greater water sharing problem than sprinklers. A year ago, near the Powder River headwaters in Wyoming, L.J. Turner's well went dry; the aquifer beneath his ranch had dropped five feet. Nearby, the drawdown was more than 600 feet. "In the summertime, you used to hear the frogs crying for rain." he says. "Now there isn't anything." There are more than a dozen coalbed methane wells on Turner's ranch. Down slope, a tawny haze hangs over Campbell County's gas rigs. Drilling began here in earnest in the mid-'90s, and in the last few years, companies have pumped between 20 and 30 billion gallons of groundwater annually.

If groundwater pumping reduces surface flows, the special master concluded, then those wells must be considered post-1950 uses under the Yellowstone River Compact. But in order to force Wyoming to curtail groundwater pumping for coalbed methane in times of scarcity, Montana will have to prove that Wyoming's deep aquifers do, in fact, feed its rivers. That won't be easy. Groundwater flow, guided by local geologic formations, is tricky to map. And water takes time to move underground, making it difficult to demonstrate cause and effect.

In the absence of data, the debate has pivoted more on faith than fact. "My sense is that coalbed methane aquifers are deeper aquifers. I do not believe that they're affecting surface water flows," says Harry LaBonde, Wyoming's deputy state engineer. His logic may stem from the fact that water law and hydrologic science have not advanced at an equal pace. Most Western states still appropriate surface and groundwater separately, under the assumption that aquifers are disconnected from streams -- an idea hydrologists dispute. But even Wyoming is starting to see flaws in this thinking. "As water tables drop more and more, that's when conflicts arise between users," says LaBonde. "And that's when we become very concerned."

In the spring of 2009, Muggli went looking for irrigation records in the old file cabinet on his grandfather's porch. He found a bundle of letters, more than 100 pages in all, thin and delicate, on carbon paper. They were all addressed to members of the Yellowstone River Compact drafting committee, of which his grandfather was a part.

"It was just a treasure trove of stuff," he says. The letters gave Muggli a sense that the drafters left some things unwritten because they trusted the states to interpret the Compact fairly. But what Muggli sees as trust could have been a simple lack of foresight -- that as water grew scarcer and technology more advanced, irrigators would scramble to make the most of their rights.

The precedent set by the Supreme Court's ruling may not reach far, particularly not to downstream states whose water allotments are quantified in interstate compacts. (The Colorado River Compact, for instance, appropriates 7.5 million acre-feet a year each to groups of upper and lower basin states.) But in states like Montana, where compacts are less specific, the decision could become problematic.

"Nobody complains in good years," says Montana Assistant Attorney General Jennifer Anders. "But what's going to happen five years down the road if Wyoming keeps consuming more without regard for downstream users?" The Supreme Court's interpretation still guarantees Montana its pre-1950 rights, at least on paper, but Anders will be watching closely when the next dry year comes. "We have a lot at stake," she says.  "It's the ability of our farmers to make a living off the land as they've done for generations."

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