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Irrigators worry as West's reservoirs run low
Availability far below average in some areas of West

Mateusz Perkowski, Capital Press 9/21/2007

Irrigation reservoirs in parts of Oregon and Idaho have been largely depleted this growing season, limiting water availability to many irrigators now and placing them in a vulnerable position for the future.

"It really sets the stage for a lot of reservoirs being really low across the state," said Jon Lea, Oregon snow survey supervisor at the USDA Natural Resources Conservation Service.

"We'll definitely need some good rainfalls or snow packs to even get us close to normal for next year," he said.


In Oregon, the Burnt, Powder, Pine, Grande Ronde and Imnaha basins have been hit the hardest: the five reservoirs in that region are at 7 percent of capacity, or about 15 percent of average, according to the USDA NRCS.

The Owyhee and Malheur basins aren't faring well either, filled to 21 percent of capacity, or 41 of average.

A few reservoirs within those regions - Warmsprings, Thief Valley and Wallowa Lake - have no water available for irrigation: zero percent of capacity, zero percent of average. Others are also expected to be "fully utilized" by the end of season, Lea said.

"The reservoirs have been used pretty heavily, and some of them have run out of water," he said.

Across the rest of Oregon, the situation is mixed. Some reservoirs have above average water levels, while others in the same basin are largely drained.

In the Willamette Basin, for example, reservoir levels range from 100 percent of average to 25 percent of average.

The variation is even greater in the Rogue and Umpqua basins: between 141 percent of average and 25 percent of average.

Overall, these basin groups, as well as the Klamath Basin, come in at above 50 percent of average.

The Upper Deschutes and Crooked basins are seeing the best reservoir levels in the state, with 90 percent of average. The Umatilla, Walla Walla, Willow, Rock and Lower John Day basins are at 74 percent of average, while the Lake County and Goose Lake basins are at 77 percent of average.


In Idaho, the Wood and Lost River basins were the most exhausted, filled to 7 percent of capacity, or 19 percent of average.

Reservoirs in the Snake River Basin were also parched. The two reservoirs in the mainstem Snake River Basin are filled to 33 percent of capacity, or 47 of average. The upper Snake River Basin, with eight reservoirs, is filled to 23 percent of capacity, or 39 percent of average.

The Bear River Basin's water levels are also insufficient, with its two reservoirs at 29 percent of capacity, or 41 percent of average.

In general, the southern and central portions of the state bore the worst of the water shortage this year, said Phil Morrisey, an NRCS hydrologist in Idaho.

"When the reservoirs become drawn down so far, (irrigators) become completely dependent on snow pack and runoff. It's a precarious position to be in," he said.

Idaho's reservoirs saw increased demand from irrigators this year due to a lack of rainfall and a change in cropping systems brought about by increased ethanol production and higher corn prices, Morrisey said.

"We've heard there's been more corn being grown," he said. "Corn is a very heavy water-use crop."

Not all of Idaho is feeling dehydrated, though. With its five reservoirs filled to 92 percent of capacity, or 99 percent of average, the northern Pan Handle has been the least affected.

"They don't see the big irrigation demand we see in southern Idaho," said Morrisey.

The Clearwater River basin and Payette River basins, are both above 80 percent of average, and other basins are at roughly 70 percent of average or above.


Reservoir levels in California are uneven as well.

For example, the Pyramid Lake reservoir in southern California filled to 89 percent capacity, or 111 percent of average, according to the California Department of Water Resources.

The Pine Flat and San Luis reservoirs in the center of the state are in much worse shape: roughly 20 percent of capacity, or 50 percent of average.

All the other key reservoirs in the state fall between these two extremes, according to the California Department of Water Resources. Unlike USDA NRCS, the department publishes figures for major reservoirs rather than basins.


Since the beginning of the year, Washington has enjoyed better snow packs, stream flows and reservoir levels than the rest of the West, and that trend has continued through the growing season.

Virtually every basin area is above roughly 90 percent of average in stored capacity, and several - the Spokane River, Lower Yakima River and north Puget Sound River basins - are above 100 percent of average.

"The water supply in Washington is in really good shape," said Scott Pattee, Washington water supply specialist for USDA NRCS.

Heavy rain in November 2006 contributed to the state's comparatively satiated reservoirs, with runoff filling reservoirs before the snow pack even had a chance to accumulate, he said.

When the snow pack did melt the following spring, "it really just topped them off," he said.

Demand from irrigators was also lighter than expected, Pattee said. "We didn't have these extreme temperatures, so I think water consumption was down from normal."

Staff writer Mateusz Perkowski is based in Salem, Ore. E-mail: mperkowski@capitalpress.com.
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