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Corps: Water Levels may Mean No Spill; Full Transport by Mike O'Bryant Columbia Basin Bulletin - February 21, 2003

An early draft of the spring and summer update for the Technical Management Team's 2003 Water Management Plan is predicting water conditions that could preclude spill and order maximum transportation for smolts at lower Snake River dams this spring.

The U.S. Army Corps of Engineers prepared the update for TMT's review this week.

The draft plan is based on a water supply forecast developed by the National Weather Service's Northwest River Forecast Center earlier this month. It shows water supply at The Dalles Dam, April through August, of 65.3 million-acre feet, about 70 percent of normal. A forecast released Feb. 21 by the center is now predicting water supply at the Columbia River dam of 67.2 maf or 72 percent of normal for the same period.

The potential that spill would be curtailed at Snake River dams doesn't change much with the updated water supply forecast. The earlier prediction shows water supply at Lower Granite Dam of 14.7 maf, 69 percent of normal, April through July, while the center is now predicting 15.7 maf, 73 percent of normal for that period. That still leaves the potential that TMT may have to curtail spring and summer spill to help salmon and steelhead smolts pass Snake River collector dams.

"With the current forecast, it is likely there will be no spill at collector dams on the Snake River this year and we will have to go to maximum transportation," said Rudd Turner of the Corps. However, he said the predicted amount of water available is on the cusp of whether the decision is certain. "In 2001, the decision was obvious. But, this is not the kind of water supply where it's so low that everything is obvious."

In 2001, during the most recent drought, the Bonneville Power Administration shut down spill at Snake River dams.

The low Snake River summer water supply is exacerbated by a lack of water in upriver water banks that are normally used to help Idaho provide 427,000-acre feet of water for summer flow augmentation. Tony Norris of the Bureau of Reclamation, along with the Spring/Summer Update, is predicting that the Bureau this year can supply between 250 and 300 kaf. He added that the Bureau has seen little response to recent rains at upper Snake River storage projects. Milner reservoir, for example, is still at 45 percent capacity, and the Boise and Payette reservoirs, where most of the rental storage is located, are 37 percent and 59 percent of normal.

According to Paul Wagner of NOAA Fisheries, the agency's 2000 Biological Opinion that governs operations at Columbia and Snake river dams allows spill at Snake River dams to be curtailed in the spring when the water supply forecast falls below 16 maf, and it calls for maximum transportation if the forecast is below 13 maf, although transportation would be used in any case if spill is curtailed. Spill would be curtailed only at the Snake River dams -- Lower Granite, Little Goose and Lower Monumental -- which have collection facilities for barging smolts downriver. Spill at some level would continue at Ice Harbor Dam, which lacks collection facilities.

However, the forecast may not preclude TMT from making some modifications to water management this spring and summer, said Ron Boyce of the Oregon Department of Fish and Wildlife. "I just want to make sure that we don't lock into a prediction that there will be no spill. There is a lot of time for more rain," he said.

The draft Spring/Summer Update also set target flows at Columbia Basin dams at a minimum level. The target spring flow for Lower Granite Dam is 85,000 cubic feet per second; at Priest Rapids Dam on the mid-Columbia River it is set at 135 kcfs; and it is set at 220 kcfs at McNary Dam. The summer flow target is set at 200 kcfs at McNary and 50 kcfs at Lower Granite.

Wagner said the BiOp calls for maximum transportation at Snake River projects if flows fall below 85 kcfs. "The question is, is there room for in-season adjustments?" he asked.

Turner said that the Corps' modeling is showing that Lower Granite flows will not reach the 85 kcfs minimum and that monthly average flows in May are more likely to be 82 kcfs. Although the BiOp is clear, with predicted flows so close to the cutoff point, Wagner thought there still might be room for management, including some amount of spill.

The update also predicts refill probabilities at Basin storage dams. While the probability for Grand Coulee is 100 percent, others are less. Refill at Libby and Dworshak dams is 90 percent probable, while it is only 50 percent at Hungry Horse Dam.

Turner said it looks like the operating agencies can provide the minimum 6 kcfs flow from Libby Dam to aid bull trout this year, but it will not be able to provide the higher level needed for a sturgeon pulse.

The low water and potential to curtail spill could affect biologists' ability to conduct some spill tests this spring, so biologists and river operators are developing a low flow study proposal that sets standards for test projects. Tim Wick of the Corps in Walla Walla said at this week's System Configuration Team meeting that the number of test days would likely decline for the Lower Granite Dam removable spillway weir test to 18 to 20 test days. Tests would alternate in four to five day blocks between 12-hour spill to gas cap and 24 hour spill for RSW operations.

In addition, the tests would be timed to avoid the peak part of the juvenile migration with some test days in mid- to late-April, followed by a break for about 80 percent of the migration, then picked up again after the peak migration has passed. The Corps will also intensify the testing by increasing the number of radio-tagged fish it will use in the test, as well as the number of hydrophones.

Worried the test could impact the bulk of the juvenile migration, Dave Wills of the U.S. Fish and Wildlife Service asked the Corps and biologists at SCT to develop a back-up plan if they cannot get enough test fish for the early part of the tests without going into the bulk of the run. However, to be as representative as possible, Bill Hevlin of NOAA Fisheries suggested it would be fine to dip into the bulk of the run.

According to TMT's update, if the Northwest River Forecast Center's March final forecast, to be released the first week of March, is less than 13 maf, then there would be no test of the removable spillway weir at Lower Granite Dam. If the April final forecast is below 16.5 maf, the test would be stopped. If it is between 13 maf and 16.5 maf, the spill test would be of the shorter duration being developed by the Corps and biologists in their low water test plan. That could set up a situation where there would be little spill for fish, but some spill for tests.

Related Sites:
Technical Management Team: www.nwd-wc.usace.army.mil/TMT/index.html