Quantifying Seepage Losses on the Truckee Canal, Derby Dam to Lahontan Reservoir

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Seepage losses from the Truckee Canal poses major challenges to water managers. Seepage losses result in inefficiencies in water delivery and cause more water than is needed by farmers to be diverted from the Truckee River to meet required demands. Increased diversions from the Truckee River result in less water flowing through the lower Truckee River system and into Pyramid Lake, a terminal lake located 25 miles north of Fernley, NV. Over the last 100 years, water diverted for the Newlands Project has resulted in reduced inflows into Pyramid Lake, decreased lake levels, which threaten the endangered fish Cui-ui (Chasmistes cujus) and Lahontan Cutthroat Trout (Oncorhynchus clarkii henshawi) endemic to Pyramid Lake. The Truckee River Operating Agreement intended to address coordination of the operation of upstream reservoirs and provide additional storage to benefit instream flows, reduce the declining water levels of Pyramid Lake and improve water quality in the Lower Truckee River. Efficient use of surface water diverted from the Truckee River for irrigation will further improve water quantity for farmers and the lower Truckee River system.

Map of the Truckee Canal and Truckee Canal divisions, Nevada

Map of the Truckee Canal and Truckee Canal divisions, Nevada. (Public domain.)

The Reclamation Act of 1902 provided funding for irrigation projects in the arid southwestern United States, including the Truckee-Carson Project, later renamed the Newlands Project. The Newlands Project was enacted to provide irrigation water to develop agriculture and encourage settlement of Lahontan Valley. The project resulted in the construction of the Truckee Canal in 1905, diverting Truckee River water through approximately 31.2 miles of canal for storage in Lahontan Reservoir. The Truckee Canal is characterized by three major reaches from Derby Dam to Lahontan:

  • Derby Reach (10 miles);
  • Fernley Reach (11 miles) and
  • Lahontan Reach (9.7 miles).

Dam and canal operations are managed by the U.S. Bureau of Reclamation (BOR), and irrigation deliveries by the Truckee-Carson Irrigation District (TCID). Approximately 26 miles of the canal is unlined with earthen embankments averaging 20 feet wide and 13 feet high.

The Truckee Canal was originally designed to convey up to 1,500 cfs with the purpose of serving the Truckee and Carson Divisions (Divisions 1 and 3) 900 cfs and a planned third division (Pyramid Division, Division 2) of 600 cfs from a siphon in the Derby Reach, approximately 6 miles downstream from Derby Dam. Within the past few decades of operation, the canal has rarely conveyed more than 750 cfs. In 2008, a section of the Truckee Canal near Fernley breached causing flooding and property damage. Since this failure, TCID has operated the Truckee Canal at reduced flows to limit risk of future failure with a maximum flow of 350 cfs. The BOR is currently evaluating options to reduce risk to public safety from future canal failures through a number of different structural improvements of the canal. The list includes lining portions of the Truckee Canal and the use of sheet pile cutoff walls to improve conveyance, strengthen the integrity of canal banks and improve safety. Further, water delivered into the Truckee Canal is conveyed in unlined sections with significant losses due to seepage. This study seeks to estimate seepage losses along the entire length of canal to improve forecasts of water delivery and provide information to BOR where problem sections are for future lining.

The BOR and TCID have expressed interest in quantifying seepage losses along sections of the Derby, Fernley and Lahontan Reaches to better understand the spatial and temporal variability of seepage losses, identify areas with high losses for prioritization of canal lining, and revise regressions relating canal flow to seepage for improved forecasts with an existing operations model. Incomplete knowledge of the seepage rates along the length of canal has resulted in less accurate predictions of flows to Lahontan Reservoir. A comprehensive seepage investigation that includes site specific data collection and modeling is needed to develop a better understanding of losses along the entire length of the Truckee Canal.

Example of monitoring equipment used along a canal transect to measure temperature and stage for the purpose of seepage estimati

Example of monitoring equipment used along a canal transect to measure temperature and stage for the purpose of seepage estimation. (Public domain.)

This study will be conducted over a 3-year period starting in fiscal year (FY) 2018. Seepage estimates will be made indirectly by numerical simulation using inverse modeling techniques based on stage and temperature measurements along 15 instrumented transects using VS2DH. Scour or fine-sediment deposition can have an effect on the temperature signal within canal sediments and can be evaluated separately to determine the influence on seepage rates.

Year One: Transect locations will be selected, surveyed, and instrumented with temperature probes and pressure transducers. Surveying and installation will be performed while the canal is dry before the irrigation season begins. Monitoring will occur over one irrigation season (March to November) with the use of temperature probes and pressure transducers deployed in piezometers.

Year Two: Data analysis and numerical modeling of seepage will be performed. This will include model development, calibration, and uncertainty analysis of 15 two-dimensional groundwater flow and thermal transport models (1 model per transect).

Year Three: A journal article summarizing the results of the study will be prepared and submitted.