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March 31, 2011 7:28 am

Flood control: More water released from Buffalo Bill

Written by Gib Mathers

The good news: Snowpack levels in the upper reaches of the Shoshone River drainages are higher than 100 percent of average.

The bad news: Snowpack levels in the upper reaches of the Shoshone River drainages are higher than 100 percent of average.

In other words, snowpack levels are sufficient to deliver water this summer for irrigation and other needs.

But, U.S. Bureau of Reclamation officials controlling the water levels at Buffalo Bill Reservoir are keeping close tabs on the snowpack. They planned to release more water into the Shoshone River below the dam beginning Wednesday night (yesterday) to make room for spring runoff later, and so lessen the potential for flooding.

“We’re going to increase our releases,” said John Lawson, the bureau’s area manager for Wyoming, during a meeting Tuesday in Powell with irrigation districts, a Wyoming Game and Fish Department representative and other stakeholders.

The reservoir has a capacity of 646,565 acre-feet, but they want to keep it around 630,000 acre-feet, said Mahonri Williams, the bureau’s chief of water and lands division.

Williams was holding his hands less than 2 feet apart, indicating the optimal level the water should be below the top of the dam.

The dam needs a little extra space in case a big, sudden storm should send surplus water rushing to the reservoir, Williams said.

That is why the dam will begin discharging more water in anticipation of high spring runoff, Lawson said.

On Tuesday, the dam was releasing 350 cubic feet per second. Right now, the river is also receiving 60 cfs from streams flowing into the canyon below the dam.

Lawson said he wants to increase releases to 1,000 cfs. The increase would be done gradually in increments of 100 cfs every 12 to 24 hours to reach the 1,000 cfs mark by early April.

The high runoff period runs from June through July, with several high inflow spikes in those months, according to the Bureau of Reclamation.

This year he anticipates a high spike in late June or early July from high mountain snowpack, Lawson said.

Lawson said he wants to adjust the outflow now so there is not excessive water in June and July.

Last year at this time, snowpack was 56 percent of average, but spring rains increased the runoff to average, Williams said.

Snowpack as of March 21 stood at 107 percent of average in the Shoshone drainages and 118 percent of average in the upper Yellowstone River drainages, according to Natural Resources Conservation Service charts.

Yellowstone’s snowpack may be an indicator of what to expect from the higher elevations flowing into the North Fork of the Shoshone. 

“We’re expecting above-average inflows,” Williams said.

They believe more water will enter the reservoir than is needed to fill the lake and serve irrigation demands. The challenge for the Bureau of Reclamation is how to store it and then release it through the dam without causing detrimental impacts downstream, Williams said.

With plenty of snow remaining in the high country, Lawson said bureau officials are taking precautionary steps.

By the end of September, Williams said bureau officials want the reservoir to contain 475,000 acre-feet, with levels dropping to 460,000 acre-feet at the end of November so surplus water does not create ice jams on the South Fork of the Shoshone, Williams said.

Concerns were voiced that too much water would damage trout spawning, but the influx will be gradual and water flow continuous, so the spawning beds should not be disturbed, Lawson said.

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