Isabella Dam is edging close to its recommended capacity

Dana Munn, the Kern River Watermaster, says June 7, 2017 as long as we maintain outflow at 5,400 cubic feet per a second, we can go over the recommended capacity of the Isabella Dam without concern. (KBAK/KBFX photo)

The Isabella Dam is pushing close to its recommended capacity of 66 percent, or 361,000 acre feet of water, for irrigation purposes. The limit was set by the Army Corps of Engineers as it works on construction of the dam.

Wednesday, the dam reached 62 percent capacity, or 349,658 acre feet. And, it's predicted to increase in capacity over the next few days, which could push the dam to its recommended capacity or at least close to it.

"This year is a 242 percent of normal precipitation year, and it's the largest year since 1983," Kern River Watermaster Dana Munn said. "In that year, we had full use of the reservoir, and there was water going over the spillway, and there was a flood control operation. There was an outflow of 7,300 cubic feet per a second coming down the canyon, but this is a big year."

Although this year is edging close to the Army Corps recommended capacity, it's not anywhere close to 1983.

Currently, outflow from the dam is flowing at 5,400 cubic feet per a second, which is the largest ordered outflow Isabella has ever seen. As long as this outflow is maintained at 5,400 cubic feet per a second, going above the Army Corps' recommended capacity shouldn't be a problem. But, outflow cannot be cut back until the 361,000 acre feet limit is maintained.

"The Army Corps says for us not to be above 361,000 acre feet, however, for flood damage purposes, they'll let us go over that," Munn said. "Currently, we are under the 361, but our modeling says that in four days we will be slightly under it. The information based upon forecasts that we get from the Department of Water Resources and the National Weather Service say we are near the secondary peaking of the supply coming in, so it appears we will peak, and then we will start to slowly drop."

For this reason, Munn says people should not worry about dam failure.

"We shouldn't be concerned about the dam. We have a very conservative operation going on," he said. "We are getting information from the state and federal officials in terms of the inflow. The Corp of Engineers is reviewing the information we provide them on our local modeling of operation, and they're giving us a lot of oversight, and they operate very conservatively, so I don't think there is a chance for a problem."

Normally, the dam can hold 568,000 acre feet of water, but in 2006 the Army Corps of Engineers dropped capacity to 361,000 acre feet for various safety reasons:

  • The Army Corps noticed seepage that might move material.
  • A fault line was discovered under the dam, which was considered "inactive" when it was first built, but is now considered "active."
  • The maximum probable flood has increased since the time it was first built, in which the Corps of Engineers will be building a bigger spillway south of the current spillway to account for the new calculations.

In terms of construction on the dam, Munn said bids are being reviewed by the Army Corps of Engineers, and if all goes as planned, construction on the dam should begin at the end of the year.

This is important because right now Kern County has been mostly tapping into Kern River. Meaning, some of the sources of water from the State Water Project and Friant Water have been displaced elsewhere, because there's already a supply available from the Kern River.

"We really want to take all this water and use it for beneficial use," he said. "We don't want it to go in the flood channel to Tulare Lake or go into the flood control facility they have at the aqueduct, which is called the Kern River Intertie, because once it goes in there, we lose utilization and the DWR takes it. ... Until the dam is reconstructed, we are limited for irrigation purposes."

Once the dam is reconstructed, it can be filled to its normal capacity of 568,000 acre feet of water

"The dam was built so the irrigation interests could store up to 570,000 acre feet during the spring runoff," Munn said. "Now we are limited to 361, so it will allow us to store roughly 200,000 acre feet of water. ... Because the Kern River is pushing water out and filling up all the spaces it can take in the county, its basically pushed out State Water Project and Friant Kern Water that would've otherwise come in. If we can hold that Kern River water up there longer, we can bring those other supplies in and have a gain of another 200,000 acre feet of water."

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