A milestone is approaching for the effort by the Modesto and Turlock irrigation districts to renew their federal license for Don Pedro Reservoir.
They plan late next month to file their draft application, a huge set of documents on how the reservoir and its powerhouse affect the Tuolumne River and nearby resources.
That would be close to the Dec.1 deadline from the Federal Energy Regulatory Commission, said Steve Boyd, director of water resources and regulatory affairs for TID, in an update to his board Tuesday.
FERC then would ask for comment over several months from environmentalists, farmers and other parties with an interest in the river. In April, Boyd said, the districts expect to file a final application that spells out how they plan to operate Don Pedro under the new license, which could be granted in 2016.
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The term of the new license has not been set. It would succeed a 1966 license that allowed the districts to build the reservoir, completed in 1971.
The relicensing will cost an estimated $50 million, TID spokesman Herb Smart said. The Turlock district is paying 68.5 percent of the cost, reflecting its share of Don Pedro water and power.
The process is of interest to people who hope to see the Tuolumne continue to provide substantial water for farming and domestic use, as well as cheap hydropower and flatwater recreation. Others say too much of the river has gone to these uses and it needs to flow higher for fish and paddlers between La Grange and the San Joaquin River.
At the same time, the State Water Resources Control Board is considering a proposal to sharply increase Tuolumne flows to enhance the Sacramento-San Joaquin Delta.
The federal relicensing, which kicked off in 2011, involves 35 studies. Many deal with conditions for salmon and steelhead trout in the lower Tuolumne, including flows, temperature, spawning gravel and the possibility that non-native striped bass might prey on native fish.
Other studies have included recreation on and around Don Pedro, plants and animals along the river and reservoir banks, artifacts from Native American use and later, and the socioeconomic benefits of the river.
Boyd noted that one study found a growing population of bald eagles at Don Pedro, a wintering spot, and another suggests that the districts might have to control Bermuda grass that has invaded native elderberry bushes.
Next month’s filing, he said, “is a summation of everything we know to date and have learned through this process.”