Studies

The following is a sample of the over 200 studies that have been performed on the Tuolumne River to determine the best course of action for the health of the river.

Spawning Gravel Study

  • The study indicates 15,694 acre-feet (25,319,653 yd3) of storage loss due to sedimentation since closure of Old Don Pedro Dam, less than 1 percent of the original storage capacity of Don Pedro Reservoir in 1971.
  • Without gravel augmentation, the channel in the first 12.4 miles downstream of La Grange Dam would slowly degrade in response to a reduction in coarse sediment supply by Don Pedro Dam.
  • The maximum estimated suitable spawning habitat areas of 1,370,917 ft2 for Chinook and 346,029 ft2 for O. mykiss occur at a flow of approximately 225 cfs based on criteria developed for this study.

Chinook Salmon Otolith Study

  • Based upon the limited number of sampling years and otoliths available for analysis by this study, it is apparent that spawning populations in the Tuolumne River exhibit low representation of early emigrating fry, with zero contributions in three out of five outmigration years analyzed and a maximum contribution of 5% in WY 2000.
  • Parr and smolt sized emigrants represented the vast majority of returning adults, implying a survival advantage for fish emigrating at larger sizes.

Chinook Salmon Population Model

  • The model is a quantitative salmon production model to investigate the influences of various factors on the life stage specific production of Chinook salmon in the Tuolumne River, identify critical life-stages that may represent a life-history “bottleneck,” and compare relative changes in population size between potential alternative management scenarios.
  • Modeling results show reduced density dependence of smolt productivity with increasing escapement.
  • Modeling results show that rearing habitat is not limiting smolt productivity under current conditions, consistent with findings of additional studies.
  • Modeling results for the base case show that smolt productivity is consistently higher in model years with increased La Grange discharge during spring.
  • Model sensitivity testing indicates that water temperature is not currently limiting smolt productivity under current conditions, consistent with findings of additional studies.

O. mykiss Temperature Study

  • The conclusion of the study is that the thermal range over which the Tuolumne River O. mykiss population can maintain 95% of their peak aerobic capacity is 17.8°C to 24.6°C, which supports the hypothesis that the thermal performance of wild O. mykiss from the Tuolumne River represents an exception to that expected based on the 7DADM criterion set out by EPA (2003) for Pacific Northwest O. mykiss.

Lower Tuolumne River Temperature Model

  • The study developed a river temperature model that simulates current and potential future water temperature conditions in the lower Tuolumne River from below Don Pedro Dam to the confluence with the San Joaquin River.
  • The results presented show that the Hydrologic Engineering Center’s River Analysis System model was able to reproduce the observed river water temperatures within a reasonable level of accuracy for both the calibration year of 2011 and the validation year of 2012.
  • The river temperature model is part of a suite of site-specific Tuolumne River models developed as part of the relicensing of the Don Pedro Project which also includes the Tuolumne River Operations Model and the Don Pedro Reservoir Temperature Model.

Floodplain hydraulic assessment

  • The goal of this study was to develop a hydraulic model for the lower Tuolumne River that simulates the interaction between flow within the main channel and the floodplain downstream of the La Grange Diversion Dam to the confluence with the San Joaquin River and to apply the model results to estimate floodplain juvenile salmonid rearing habitat.
  • Overall, the results of the study show flows above bankfull discharge are associated with increases in habitat area for juvenile life stages of lower Tuolumne River salmonids. Although some floodplain areas are present over the length of the lower Tuolumne River, because of the history of anthropogenic changes to in-channel and floodplain areas not all portions of the river are inundated at the same flows.