The federal government has ordered a new look at how the 120-year-old La Grange Dam, a small impoundment two miles downstream from Don Pedro Reservoir, affects the Tuolumne River.
In a ruling that draws on some intriguing history about the river, an official found that the dam and adjacent hydroelectric plant need a license from the Federal Energy Regulatory Commission.
The Modesto and Turlock irrigation districts, which own the dam, already are in the midst of an expensive relicensing process for Don Pedro. It mainly deals with how much water should be released into the lower river for fish.
It is unclear how much the La Grange requirement could cost.
"The districts are currently reviewing the FERC order regarding La Grange Dam and evaluating its findings," MID spokeswoman Melissa Williams said by email.
Environmentalists see the ruling, issued last week, as a chance to rework the water and power system to benefit salmon.
"There have always been ups and downs in the salmon population over the years, but the last 10 years represent the longest sustained crash in the history of the river," said Patrick Koepele, deputy executive director of the Tuolumne River Trust, in a news release.
The 21-page order was from Edward Abrams, director of hydropower administration and compliance at FERC.
The districts completed La Grange Dam in 1893, six years after they came into being. The 127-foot-high structure diverted water to the MID's main canal on the north side of the river and to the TID's on the south side.
It was their primary water storage until 1923, when the much larger Old Don Pedro Dam was completed upstream. La Grange Dam remained in place, catching releases from Old Don Pedro and supplying the canals.
Continues to feed canals
The even larger New Don Pedro Dam was completed in 1971. It created today's main reservoir, seven times the size of Old Don Pedro.
La Grange Dam continues to feed the canals. It also supplies a 4.9-megawatt power plant, about a 50th of the output of Don Pedro's turbines. The plant's presence put La Grange under the purview of FERC, which issues licenses that try to balance power needs with fishery concerns.
The ruling does not say why La Grange has gone so long without a license, but it does say that one is needed now.
The requirement kicks in if a dam backs up water onto federal land, and La Grange does this on acreage owned by the U.S. Bureau of Land Management, Abrams said.
A license also is required if the river stretch at issue has ever been navigable, he wrote.
Abrams cited circa-1850 accounts of gold-seekers boarding converted whaling boats in Stockton and heading up the San Joaquin and Tuolumne rivers. At the time, the rivers had no major diversions and often flowed high in winter and spring.
Even today, Abrams said, canoes and other small boats can ply the Tuolumne almost up to the base of La Grange Dam, although access from the banks is limited by private landowners. He noted that California Department of Fish and Game employees count spawning salmon each fall in a 15-foot boat powered by an outboard motor.
The river, Abrams wrote, "is used or suitable for use by recreational boaters from the La Grange Dam and powerhouse to the San Francisco Bay, thus demonstrating its suitability for use for the simpler forms of commercial navigation."
The licensing process could improve fishery flows on a river that already is heavily used for irrigation and domestic water, Koepele said.
"While we support a healthy ag-based economy, it doesn't have to come at the expense of a healthy Tuolumne River," he said. "We are eager and committed to finding workable solutions that allow for both."
The MID and TID already provide certain flows for fish under the Don Pedro license. They contend that salmon also would benefit from other measures, such as reducing predation by non-native striped bass and pollution in the Sacramento-San Joaquin Delta.
Bee staff writer John Holland can be reached at email@example.com or (209) 578-2385.