Feds deny request to keep Don Pedro Reservoir spillway open; closure could come Monday

Federal officials on Friday denied a request to keep the Don Pedro Reservoir spillway open, to the chagrin of operators concerned about future storm runoff in their Tuolumne River watershed.

The U.S. Army Corps of Engineers said the spillway must be closed to reduce the threat of flooding on the lower San Joaquin River, which is fed by the Tuolumne. A spokesman said the decision could change based on conditions.

The Turlock Irrigation District, which manages Don Pedro, expects to close the spillway by Monday to comply with the decision.

The Tuolumne has flowed at about 16,000 cubic feet per second since the spillway opened Monday. This has caused moderate flooding on its banks but has created more space in Don Pedro for upcoming storms and spring snowmelt.

The Corps of Engineers ordered the flow reduced to 11,300 cfs, which is still far higher than the average volume.

The district had hoped to keep it open as long as needed to get the reservoir surface down to 815 feet above sea level. It was at 828.84 feet as of late Friday afternoon, a little more than a foot below capacity.

TID, which owns the reservoir with the Modesto Irrigation District, had enlisted several business and government leaders to petition the corps on the issue.

Stanislaus County Supervisor Vito Chiesa said Friday that the threat to levees on the lower San Joaquin has abated because of reduced flows in two uncontrolled streams – Dry Creek in Modesto and Orestimba Creek near Newman.

He said the greater threat lies upstream of Don Pedro, which could get more winter storms or an early warm spell that accelerates snowmelt.

“It’s very precarious,” Chiesa said. “I think what (TID) is asking for is very logical.”

The Don Pedro spillway opened for only the second time since the reservoir’s completion in 1971. The first was in 1997, when the flooding was far worse.

The corps coordinates reservoir releases around the Central Valley, a tough balancing act in one of the wettest winters on record.

Tyler Stalker, a spokesman in the agency’s Sacramento office, said it weighed TID’s concern about upstream runoff with the need to prevent flooding on the San Joaquin around Manteca.

“The primary reason at this time is a lot of levee distress down on the San Joaquin River,” he said. “We understand and are aware of their concern moving into the spring snowmelt season.”

A news release from TID put it this way: “Snow sensors are recording a historic snowpack ready to unleash millions of acre-feet of additional inflow into Don Pedro when significantly warm storms or warm weather unfold in the coming months.”

This story was originally published February 24, 2017 at 4:38 PM with the headline "Feds deny request to keep Don Pedro Reservoir spillway open; closure could come Monday."