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Rapid Washington snowmelt fills streams

Dan Wheat

Capital Press

Published on May 5, 2016 9:34AM

Last changed on May 6, 2016 2:55PM

The Wenatchee River runs full under railroad and highway bridges at the north end of town, May 4. Rivers draining the east slopes of the Cascade Mountains have been full for a month from substantial mountain snowmelt.

Dan Wheat/Capital Press

The Wenatchee River runs full under railroad and highway bridges at the north end of town, May 4. Rivers draining the east slopes of the Cascade Mountains have been full for a month from substantial mountain snowmelt.

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YAKIMA, Wash. — April was a month of rapid snowmelt in the Washington Cascades giving irrigators plenty of water, but it may not last into late summer in valleys with little or no reservoirs.

Pear orchards in certain parts of the Wentachee Valley, orchards to the north in the Entiat Valley and orchards and hay fields even farther north in the Methow and Okanogan valleys may run low on water in August and September.

Junior water right holders in the Yakima Basin are forecast at 85 percent of the normal supply by late summer, the U.S. Bureau of Reclamation announced May 5. That shouldn’t affect irrigators such as the Roza Irrigation District and Kittitas Reclamation District but means they and other juniors will need to be careful with water, a USBR official said.

“We’ve seen the fastest melt rate we’ve ever seen — record rates or second-fastest rates in over 80 percent of our SNOTEL (snowpack telemetry) sites with 15 years or more of data,” said Scott Pattee, water supply specialist with the Natural Resources Conservation Service in Mount Vernon.

“Sites below 5,000 feet have melted out two to three weeks early and right now the snow level is 5,000 to 5,500 feet,” Pattee said.

Statewide snowpack was 107 percent of normal on April 5 but had dropped to 73 percent of normal by May 4, he said. The best snowpack all winter was in the upper Columbia (Okanogan and Methow basins), but that’s now 68 percent versus 134 percent a month ago, he said.

May 5 through September streamflow forecasts are reflecting the earlier than desired loss of snowpack, Pattee said.

Some of those forecasts by percent of average flow are: Spokane basin, 78 to 98; upper Columbia, 86 to 101; central Columbia 87 to 103; upper Yakima, 67 to 74; lower Yakima, 72 to 94; lower Snake, 75 to 93; lower Columbia, 89 to 99; and Olympic Peninsula, 73 to 75.

Rapid snowmelt has caused the highest unregulated flows in the Yakima River at the USBR station at Parker, which is 3 miles southeast of Union Gap, in the past 35 years and the second-highest in the past 90 years, said Chris Lynch, USBR hydrologist in Yakima.

The Wenatchee River and other rivers draining the east slopes of the Cascades have been running full for a month. The only thing that’s prevented flooding has been that there was little to no rain, Pattee said.

Precipitation at the five water reservoirs in the Yakima Basin was 14 percent of average in April which is a new record beating 15 percent for that month set in the 1930s and 1950s, Lynch said.

“I don’t want to raise any big alarms, but it’s a very interesting statistic,” he said.

It means April was a very dry month which by itself may not mean much but would if March had been dry, he said. May usually is drier than April.

As of May 3, the five Yakima reservoirs were 94 percent full and 126.7 percent of the average from 1981 through 2010.

“We hope to have them full by mid to late May and be able to make it into June before we start drawdowns for irrigation,” Lynch said.

Irrigation diversion for the Kittitas, Roza and all other irrigation districts upriver from Parker were at 5,065 cubic feet per second on May 3. But that’s all water passing through the reservoirs, spilled to regulate the reservoirs with irrigation being a byproduct, Lynch said. He hopes to stave off drawdowns for irrigation until early June. It started in early April in last year’s drought and the Roza and Kittitas districts lost crops to substantial loss of normal water supply.



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