TID’s Upper Dawson Hydroelectric Project

  • by Turlock Irrigation District
  • Jun 7, 2023

While the founders of Turlock Irrigation District (TID) constructed a well-thought-out water system more than 135 years ago, innovation and enhancements to properly steward TID’s precious resource continue to be part of the District’s practice. The Upper Dawson Hydroelectric Project is an example of TID’s innovation and resourcefulness in maintaining the District’s infrastructure and preserving the integrity of the Tuolumne River until it reaches its growers.

Dawson Reservoir is part of the off-stream TID canal system and has three dams that make up the Upper and Lower Dawson Reservoirs. Built in 1983, the Upper Dawson Hydroelectric Project consists of a 41-foot max high embankment fill dam, a 4.45 Megawatt Powerhouse generating carbon free hydropower and a concrete overpour spillway weir structure. The Dawson facility is an inline canal facility that passes all TID irrigation flows delivered by Don Pedro Reservoir and is subject to uncontrolled precipitation inflows from McDonald Creek.

During the irrigation off-season in 2021, TID implemented capital improvements to the spillway to increase capacity and maximize water operational efficiencies. The project was completed in February 2022.

For this project, the District added two new, automated 6 feet-10 inches wide by 8 feet high stainless steel bulkhead gates to an existing larger, non-operational weir board opening within the spillway structure that was added during original construction. Tied to the District’s Energy Management Systems (EMS) and Supervisory Control and Data Acquisition (SCADA) systems, the gates have the ability to be left in automatic reservoir level control where human involvement is not needed, or can be placed in remote control for operation by personnel in TID’s main office, or local manual control for operation by staff inside the Powerhouse.

This modification ensures the passage of irrigation flows without reducing the reliability of Don Pedro Powerhouse electricity generation during the season, as well as passage of increasingly variable rain events in the McDonald Creek watershed during the winter and into early irrigation season.

The Dawson Powerhouse was designed as the primary conveyance for irrigation flows. In the event of the Dawson unit coming offline, the spillway was intended to pass the irrigation flows without interruption to the canal system above it. However, during a more in-depth review of the facility, a spillway capacity deficiency was discovered that at higher flows would encroach the reservoir elevation into the embankment dam’s freeboard buffer.

This project was prudent to ensuring continued reliable irrigation and electricity deliveries, as well as reducing risk to downstream District facilities throughout the year. Prior to the addition of the gates, District operators were required to lower peak irrigation flows from Don Pedro, limiting both water and electrical deliveries, in order to maintain a safe freeboard on Dawson Dam in the event of a unit trip.

This project supports the carbon free, hydroelectric generation of Don Pedro and irrigation reliability of the District’s Upper Main Canal system, unhindered during any range of flows. The gates increase the flow capacity of the Dawson facility by 50% as compared to previous design capacities. The gates also reduce risk to the irrigation system that supplies 150,000 acres of some of the most valuable and productive farmland in the world.