Abstract

Total dissolved gas (TDG) supersaturation, which occurs during dam spilling, may result in fish bubble disease and mortality. Many studies have been conducted to identify the factors pertaining to TDG generation, such as the spilling discharge and tailwater depth. Additionally, the energy dissipation efficiency should be considered due to its effect on the air entrainment, which influences the TDG generation process. According to the TDG field observations of 49 cases at Dagangshan and Xiluodu hydropower stations, the TDG was positively related to the energy dissipation efficiency, tailwater depth and discharge per unit width. A correlation between the generated TDG level and these factors was established. The empirical equations proposed by the USACE were calibrated, and the TDG level estimation performance was compared with the established correlation for 25 spillage cases at seven other dams. Among the considered cases, the standard error of the TDG estimation considering the energy dissipation efficiency was 5.7%, and those for the correlations obtained using the USACE equations were 13.0% and 10.0%. The findings indicated that the energy dissipation efficiency considerably influenced the TDG level, and its consideration helped enhance the precision of the TDG estimation. Finally, the generality of this approach and future work were discussed.

Highlights

  • Total dissolved gas (TDG) supersaturation, which occurs during dam spilling, may result in fish bubble disease and mortality

  • The methods to predict the supersaturated TDG generation can be divided into 3 types: mechanical models, numerical models and empirical equations

  • Due to upper dam spilling, all the forebay TDG levels are higher than 100%, especially at the Dagangshan hydropower station

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Summary

Introduction

Total dissolved gas (TDG) supersaturation, which occurs during dam spilling, may result in fish bubble disease and mortality. The relations between the generated TDG level and the energy dissipation efficiency, discharge per unit width and tailwater depth were explored based on TDG measurements in the Dagangshan and Xiluodu projects. The tailwater depth ( ht ), discharge per unit width (q ), energy dissipation efficiency ( E ) and forebay TDG level (G f ) were selected to estimate the TDG level: Gs − Gf Gf

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