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Hells Canyon Complex Total Dissolved Gas Study

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Hells Canyon Complex Total Dissolved Gas Study Hells Canyon Complex Total Dissolved Gas Study Ralph Myers Project Limnologist Sharon E. Parkinson Principal Engineer Technical Report Appendix E.2.2-4 March 2002 Revised July 2003 Hells Canyon Complex FERC No. 1971 Copyright © 2003 by Idaho Power Company Idaho Power Company Hells Canyon Complex Total Dissolved Gas Study TABLE OF CONTENTS Table of Contents ............................................................................................................................. i List of Tables...................................................................................................................................ii List of Figures .................................................................................................................................ii List of Appendices .........................................................................................................................iii Abstract ........................................................................................................................................... 1 1. Introduction ................................................................................................................................ 2 2. Study Area.................................................................................................................................. 3 3. Plant Operations ......................................................................................................................... 4 4. Methods...................................................................................................................................... 5 5. Results and Discussion............................................................................................................... 6 5.1. TDG and Project Operations............................................................................................. 6 5.1.1. Measured TDG Data ................................................................................................. 6 5.1.2. Predictive Numerical Model Development.............................................................. 8 5.2. Spill Manipulation Test................................................................................................... 10 5.2.1. Brownlee Dam........................................................................................................ 10 5.2.2. Hells Canyon Dam ................................................................................................. 11 5.3. Downstream Dissipation of TDG.................................................................................... 11 5.4. Physical Modeling of Hells Canyon Dam....................................................................... 12 6. Summary and Conclusions....................................................................................................... 13 7. Acknowledgments.................................................................................................................... 14 8. Literature Cited ........................................................................................................................ 14 Hells Canyon Complex Page i Hells Canyon Complex Total Dissolved Gas Study Idaho Power Company LIST OF TABLES Table 1. Physical characteristics of Brownlee, Oxbow, and Hells Canyon powerhouses and dams.......................................................................................... 17 Table 2. Equations used to describe spill vs. total dissolved gas relationships at the projects of the Hells Canyon Complex. ................................................................ 17 LIST OF FIGURES Figure 1. Total dissolved gas study area............................................................................... 19 Figure 2. Brownlee Dam study area showing reservoir, turbine discharge, and spillway sampling sites.......................................................................................... 21 Figure 3. Oxbow Dam study area showing reservoir, turbine discharge, and spillway sampling sites. ....................................................................................................... 22 Figure 4. Hells Canyon Dam study area showing reservoir and tailwater sampling sites........................................................................................................................ 23 Figure 5. Mean daily Snake River flow (cfs) measured downstream of Hells Canyon Dam from October 1996 through August 1999. ................................................... 24 Figure 6. Total dissolved gas levels in water at six locations: (1) Brownlee Reservoir, (2) Brownlee Project discharge (spill and turbine), (3) Oxbow Reservoir, (4) Oxbow Project discharge (spill and turbine), (5) Hells Canyon Reservoir, and (6) Hells Canyon Project discharge on 8 dates in 1997....................................................................................................... 25 Figure 7. Total dissolved gas levels in water at six locations: (1) Brownlee Reservoir, (2) Brownlee Project discharge (spill and turbine), (3) Oxbow Reservoir, (4) Oxbow Project discharge (spill and turbine), (5) Hells Canyon Reservoir, and (6) Hells Canyon Project discharge on 8 dates in 1998....................................................................................................... 26 Figure 8. The relationship of spill and total dissolved gas measured during spill at Brownlee Dam, 1997−1998. ................................................................................. 27 Figure 9. The relationship of spill and total dissolved gas measured downstream of Oxbow Dam during spill, 1997–1998................................................................... 27 Page ii Hells Canyon Complex Idaho Power Company Hells Canyon Complex Total Dissolved Gas Study Figure 10. Change in percentage of total dissolved gas saturation between Oxbow Reservoir and the Oxbow spillway. ...................................................................... 28 Figure 11. Percentage of TDG saturation measured at the Hells Canyon boat ramp downstream of Hells Canyon Dam, 1997–1988. .................................................. 29 Figure 12. The relationship of spill and total dissolved gas measured during spill at Hells Canyon Dam, 1997–1999. ........................................................................... 30 Figure 13. Total dissolved gas levels measured while releasing 39,000 cfs of spill from Brownlee Dam on June 4, 1998, and 28,000 cfs of spill at Hells Canyon Dam on June 3, 1998...................................................................... 31 Figure 14. Downstream dissipation of total dissolved gas within Hells Canyon relative to the 110% saturation standard. .............................................................. 32 Figure 15. General sectional view of the Hells Canyon Dam spillway model constructed by researchers at the Iowa Institute of Hydraulic Research (IIHR).................................................................................................................... 33 Figure 16. Location of crest gates, nappe deflectors, and sluice gates on the Hells Canyon Dam spillway.................................................................................. 34 Figure 17. General view of the modified deflector configuration for the Hells Canyon Dam spillway developed using the two-dimensional model................................. 35 Figure 18. Deflector performance from the evaluation of the IIHR two-dimensional physical model....................................................................................................... 36 LIST OF APPENDICES Appendix 1. Hells Canyon Flow Deflector Design Report. ...................................................... 37 Hells Canyon Complex Page iii Hells Canyon Complex Total Dissolved Gas Study Idaho Power Company This page left blank intentionally. Page iv Hells Canyon Complex Idaho Power Company Hells Canyon Complex Total Dissolved Gas Study ABSTRACT As is the case with most hydroelectric projects, spilling water at projects in the Hells Canyon Complex causes total dissolved gas (TDG) levels to exceed the 110% saturation limit for protecting aquatic biota. Levels in the tailwater of Hells Canyon Dam have been measured as high as 135% saturation, with resulting in-river levels in excess of 110% saturation for up to 60 miles downstream. Measured levels in the tailwater of Brownlee Dam approach 125% saturation, with little dissipation downstream through Oxbow and Hells Canyon reservoirs. A predictive numerical modeling tool was developed as a part of this study to provide TDG boundary condition information to water quality and habitat models for resource impact evaluation. Based on the results of spill tests, spilling water from the upper spill gates at Brownlee Dam helps minimize TDG levels in the tailwater. Also, physical modeling of Hells Canyon Dam shows that flow deflectors installed on the dam’s spillway may reduce TDG levels at total spill flows of less than 30,000 cubic feet per second. Although flow deflectors show promise for reducing elevated TDG levels at a qualitative modeling level, it is difficult to predict what levels of TDG will occur below the project under all spill conditions with the deflectors in place. Hells Canyon Complex Page 1 Hells Canyon Complex Total Dissolved Gas Study Idaho Power Company 1. INTRODUCTION Total dissolved gas (TDG) is a measure of the sum of partial pressures of all dissolved gases, including
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