The equivalent of four additional Stampede Reservoirs would be needed to achieve future baseline level water shortages, and any new water storage projects should be considered, according to a report presented Wednesday to the Truckee Meadows Water Authority (TMWA).
Additionally, the report said Lake Tahoe is sensitive to increases in evaporation at more than 3 feet annually and irrigation demands will increase as temperatures rise.
Results of a recent federal Bureau of Reclamation Truckee Basin Study were brought to the TMWA board. TMWA, Tahoe Regional Planning Agency, Truckee River Flood Management Authority, and Placer County Water Agency were partners in the study with the bureau, an arm of the Interior Department.
“We wanted to look at what’s happening to the snowpack, what’s happening to the runoff, and how reservoirs are filled,” said Arlan Nikel, Reclamation Bureau senior project manager and landscape architect. “What’s happening to groundwater charge, recharge, and discharge? Also, we wanted to look at what’s happening to water supplies under increasing temperatures.”
Historically, basin reservoirs have refilled in April and have begun drawdown in late summer. But peak runoff could eventually begin as early as February by the year 2100, Nikel said. If the snowpack is lighter and not available to refill reservoirs, declines gradually occur in reservoirs from one year to the next if average precipitation isn’t constant.
“Does that mean we’re going to potentially have to rethink how and where we store water? In other words, instead of storing it on the surface and trying to push it down into the aquifers?” TMWA Chairman Vaughn Hartung asked Nikel.
“Yes,” Nikel said. “All forms of storage are needed to be considered moving forward under future conditions.”
Among suggestions offered by the Reclamation Bureau study:
- Allow Truckee-Carson Irrigation District carryover storage in the Truckee River reservoirs and remove storage limits
- Change balance of credit storage available to users at Truckee River reservoirs
- Modify flood control curves to adapt to climate and modify operating and criteria procedures at Lahontan Dam to improve success of refill
- Consolidate agricultural water rights, convert to low water-use crops
- Revise flow targets to correspond with peak flows under climate change
- Augment the Truckee Canal capacity
- Capture spills from Donner, Prosser Creek, Martis Creek, and Boca reservoirs
- Expand Truckee River Operating Agreement water supply operations model into California
TMWA executive director Mark Foree said it’s been a long time since the utility has looked for additional storage sites but it plans to begin searching for them as it looks to the future. Obstacles to some suggestions include land and permitting costs, he said.
TMWA is also in the process of updating its water resource plan.