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Below-Average Snowpack in Clearwater Basin Calls for Early Fill of Dworshak Reservoir by Staff Columbia Basin Bulletin, April 24, 2015

Below-average snowpack in the Clearwater sub-basin and uncertain inflows from future weather conditions add up to an earlier-than-normal fill planned for Dworshak Reservoir, according to U.S. Army Corps of Engineers water-management officials.

"This is an unusual year for water management," said Steve Hall, water management program manager at The Corps' Walla Walla District. "The water-supply forecast for April through July is 70 percent of normal; last year at this time, the water supply forecast was 128 percent of normal. As a result, we have to manage the reservoir quite differently this year.

"We plan to fill the reservoir several weeks earlier than usual to ensure adequate water supply to meet flow-augmentation requirements in the Snake River and offer optimal reservoir recreation conditions for as long as possible," said Hall. "Analysis indicates we still need to maintain some space in the reservoir for flood-risk management purposes, but we are well on our way to being within 10 feet of full pool (1,590 feet in elevation) by the end of April. And, unless the weather brings in significantly greater precipitation than what the National Weather Service forecasts currently project, we plan to bring the reservoir to full pool (1,600 feet) around the end of May, or earlier if flood-risk analysis allows it."

Because snowpack in the sub-basin is 64 percent of normal, there is a possibility the Corps may be required to start flow augmentation earlier this year, but it is too early to tell because future precipitation and temperatures are unknown variables. Water managers say they will continue to monitor inflows and snowpack, and will keep the public informed of significant changes in reservoir operations.

Dworshak's natural resources staff and maintenance crews are preparing lakeshore recreation sites for early season visitors and campers.

"Conditions are already great for visitors -- all boat ramps are open, the reservoir is only 12 feet from full making access to shoreline campsites unusually easy for this time of year," said Paul Pence, Dworshak NRM. "Lots of bass fishermen have been heavily using the lake, and coming back with smiles and reports of very large fish being caught. We're also seeing an increase in special-use permit applications by small clubs to hold fishing tournaments."

Managing water levels to reduce flood risk throughout the reservoir system requires constant monitoring of weather and snow-pack, plus making appropriate adjustments to ensure enough water is stored in reservoirs to meet operational requirements while still maintaining adequate space for flood-risk management purposes.

The Corps advises Clearwater River boaters and other people using regulated waterways to always be alert to changes in water elevation and volume of flow. Current water-management conditions can be viewed online at www.nww.usace.army.mil/Missions/WaterManagement.aspx.

Water managers are sensitive to the increased drought potential this year and are collaborating with regional partners to manage regional water supply to meet critical obligations, Hall said.

Because many reservoirs had some fill carry-over from last year, water managers anticipate adequate water supply in most sub-basins within the Corps' Northwestern Division, this year, Hall said. Although snowpack in the Cascade Mountains is extremely low (single digits), snowpack in the upper-Columbia Basin, primarily Canada, is closer to normal levels. Eastern Oregon basins, however, have experienced significant lower snowpack and inflows than other sub-basins.

A fact sheet about Dworshak Reservoir operation is available on the Walla Walla District website at www.nww.usace.army.mil/Portals/28/docs/dworshak/FS_DworshakReservoir150420.pdf.

Meanwhile, in the Yakima Basin, the Bureau of Reclamation released a mid-April 2015 Total Water Supply Available forecast because of the decline in reservoir storage and low stream flows.

The TWSA indicates a full water supply for senior water rights during the 2015 irrigation season, but an estimated 54 percent supply for junior water rights. Reclamation will issue water supply forecasts monthly or as needed at least through July.

"The weather conditions forced us to use storage to meet demands starting April 15," said Chuck Garner, Yakima Project River Operations supervisor. "We had hoped conditions would favor full reservoirs into May and a later start of prorationing."

The mid-April TWSA forecast is based on flows, precipitation, snowpack, and reservoir storage as of April 15, along with estimates of future precipitation and river flows. Other future weather conditions that help determine the timing of the run-off and the demand for water are also critical in determining stream flows, prorationing, and reservoir storage.

"The record low snowpack, the cold weather and the low amount of April precipitation caused a decline in the natural flows as well as a decline in the water supply and prorationing," said Garner.

Unfavorable spring weather could further reduce prorationing while favorable conditions could improve it. Since longer term weather conditions are unpredictable, Garner recommends that water conservation be considered by all users in the Yakima Basin.

For more information, visit the Bureau of Reclamation website at www.usbr.gov/pn/hydromet/yakima

Related Sites:
Water Supply: Early Runoff Depleting Snowpack, Columbia River At Dalles Dam Projected At 82 Percent by Staff, Columbia Basin Bulletin, 4/10/15

Related Pages:
watch Dworshak Reservoir Early Water Released Due to High Temperatures by Sophie Miraglio, KLEW TV, 7/3/13