With Rye Patch Reservoir more than 85 percent full, Lovelock Valley farmers have another good irrigation year to look forward to. Last week, the reservoir, that can store a maximum of 213,000 acre-feet of water, was holding about 187,160 acre-feet of water courtesy of the Humboldt River.
The Pershing County Water Conservation District kicked off this year’s irrigation season on March 15 with a water allotment for farmers of 2.25 acre-feet per acre. This month, the district’s board of directors considered an increase to 2.5 acre-feet but delayed that decision by a month or two until they see how the water supplies hold up after the spring runoff.
A key consideration is the flow of the Lower Humboldt River that’s expected to decrease as the irrigation season progresses unless a major storm occurs. On April 11, the river’s flow at Palisade had increased to 728 cfs (cubic feet per second) while the flow at Imlay was stable at 465 cfs according to the USGS. The average flow at Imlay is 300 cfs over the last 70 years.
Other factors to consider are saving adequate water for next year’s crops and the efficiency of the irrigation system. Ditches have been filling up faster this year due to last year’s big snowpack and runoff that restored groundwater meaning less ditch water is lost to the ground.
The April “water picture” indicates the current water allotment of 2.25 acre-feet and an estimated 63 percent irrigation efficiency could leave 39,050 acre-feet of “carry over” water in storage. A full water allotment of 3 acre-feet at 67 percent efficiency would leave only about 19,233 acre-feet of carry over water for next year, according to PCWCD Manager Bennie Hodges.
Hodges suggested the district’s board of directors wait until June and take another look at the water picture and irrigation efficiency before they decide to increase their 2018 water allotment.
“It looks pretty good right now,” Hodges told the board last week.
The maximum allotment allowed by the state is three acre-feet per acre. In 2017, the state water engineer allowed the district to deliver up to four acre-feet after years of drought and little or no water for local farmers. Not everyone could use that much water but the surplus did help to restore the Lovelock Valley’s groundwater and irrigation efficiency according to local farmers.
The latest news on the hydroelectric power plant was mixed. The turbine and generator are ready to produce power for the grid and income for the district, but NV Energy is not able to provide adequate power to operate the equipment, according to project consultant Larry Rackley.
As a result of the electrical problems, the power plant remains idle as irrigation water rushes by below Rye Patch Dam. That means lost water power revenue for the district and, when the irrigation season ends in the fall, there will be no water released to spin the power plant turbine.
In a good water year, the water power was expected to generate an estimated $150,000 worth of electricity during the irrigation season and up to $200,000 during a big water year. The per kilowatt-hour rate paid by NV Energy will vary according to market demand and other factors.
The latest delay in power production did not stop the district’s clean energy rebate that finally arrived last week. After NV Energy deducted its “true-up” costs for the project of $72,631 from the $650,000 rebate, the district got a check for $577,369. Rackley said the charges exceed the utility’s original estimate by 57 percent. He’s challenging some of the labor and other costs.
Rackley reminded NV Energy that the irrigation district saved ratepayers between $200,000 and $300,000 by resolving a right of way issue for a utility easement without costly litigation.
Rackley said the utility is not charging for its latest electrical work to plug in the power plant.
“They have a big nut to crack to fix whatever is insufficient on their system,” he said. “It’s going to be a big dollar for them. It’s in their court as to when Bennie and I can meet with them and go over their charges.”
Shane Dyer of Dyer Engineering said the reservoir water storage capacity could be increased without sacrificing dam safety if the district is willing to make costly investments in the dam.
Increased water storage of up to 50,000 acre-feet would raise the reservoir level and put more pressure on the 80-year-old dam meaning structural upgrades and/or an additional spillway. There could be water rights issues as well as land issues if the reservoir expands, Dyer said.
Alternatives include increasing the height of the dam’s radial gates, increasing the “sill” at the bottom or the additional spillway to increase maximum water release rates during floods. Structural changes to increase storage capacity could cost upwards of $5 million, Dyer said.
Worst case floods, that may happen only every 30,000 years, must be factored in, he said. The maximum flood on record increased the river to 7500 cfs at Rye Patch according to Hodges.
“The first thing we found was the PMF (Probable Maximum Flood) is really big — it’s 68,000 cfs,” he said. “They have it exactly to the top of the dam. When we saw that number from the Bureau of Reclamation, we didn’t think it makes sense and that it needs to be recalculated. The thing that’s limiting your storage is this hypothetical storm that you have to store and route through.”
Reducing the PMF could increase reservoir storage but dam safety officials would have to accept the engineer’s new calculations on worst case flood scenarios, Dyer said. Part of the storage increase could be mitigated by water releases as needed to prevent flooding, he said.
“Depending on the depth of the storm, we could open the spillway to accommodate the storm,” he said. “We could take it to dam safety and see how they felt about that.”
Dyer said his firm will re-calculate the PMF for the Rye Patch area and the costs of structural changes to the dam that might be needed to safely increase the reservoir storage capacity.