Turlock Irrigation District wants to continue releasing more water out of the Don Pedro Reservoir sending it down the Tuolumne River and into the San Joaquin River past the fragile levees protecting rural south Manteca and the Lathrop levees that are now experiencing seepage.
The Army Corps of Engineers denied the request.
The request was based on concerns that the dam — that is still a foot from its maximum elevation of 830 feet despite the spill gates being open since Monday for a pumped up outflow of 16,000 cubic feet per second — needs to make room for what is expected to be a near record spring snowmelt as well as any upcoming storms.
The denial was based on what is happening to levees along the Tuolumne and San Joaquin rivers and the struggle that is underway to keep them from failing.
The Army Corps is struggling to play a precarious balancing game that involves saturated levees, record snowpack, and reservoirs filled to the brim.
With the denial on Friday, TID expects to close the spillway gates within the next two days. The action will pare back outflows with the lake still at 99 percent capacity.
Inflow Friday into Don Pedro was 14,500 cubic feet per second compared to the outflow of 16,000 subic feet per second.
Dam operators were hoping to continue flows until the lake reached 815 feet above sea level, which would likely require the spillway to remain open for the foreseeable future.
A warm storm rolling across Northern California could be disastrous at Don Pedro – melting some of the record snowpack in the mountains above the reservoir and forcing the decision to release yet even more water even though the lower San Joaquin River is nearly bursting at the seams.
In a press release Tuesday, TID said it had “gathered support from downstream stakeholders for this deviation. More than 15 affected local public agencies, governing bodies, elected officials and businesses petitioned the Army Corps for the deviation because it is necessary to prevent future Tuolumne River flows at levels greater than currently being experienced. Many downstream stakeholders would rather maintain the Tuolumne River and San Joaquin River at their current flow rates and elevations for an acceptable period of time, rather than see flows and elevation drop significantly only to watch them rise to historic levels later this year due to historic rainfall and snowpack runoff.”
Meanwhile New Melones Reservoir is now at 63 percent of its 2.4 million acre feet of capacity. The inflow is at 8,461 cubic feet per second while the outflow is a paltry 47 cubic feet per second.
Other dams on the San Joaquin River watershed have also all had their releases dialed back to between 127 and cubic 175 feet per second. Releases ultimately flow past the levees protecting rural Manteca and Lathrop. The current capacity levels of those reservoirs at McClure on the Merced River at 93 percent, Friant on the San Joaquin River at 87 percent, and Buchanan on the Chowchilla River at 82 percent.
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