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Step-by-step process of calculating the average concentration from measurement data by polynomial fitting and deconvolution.
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In Norway, a recent project used a risk matrix to identify about 200 hydropower plants ( 11 % of the total number) of being in high risk of producing air-supersaturated water. The combined installed capacity of these hydropower plants amounts to more than 45 % of Norway’s total installed hydropower capacity. Total dissolved gas (TDG) supersaturatio...
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Rivers across the world are increasingly fragmented due to anthropogenic barriers, with the restoration of connectivity often using fish passes. Fish passes are, however, usually designed for anadromous species, despite ecologically important non-anadromous species being present in the communities impacted by fragmentation. To assess the outcomes f...
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... Finally, the results obtained in this study are compared to the k L a during the natural degassing process of TDG supersaturated water in a river downstream a Norwegian hydropower plant. Those results were obtained from measurement data provided by The Norwegian Research Center (NORCE) [89]. A direct comparison is visible in Fig. 8. ...
... It seems likely that this failure to detect a significant difference was the result of differences in the distribution of data (i.e., much more data) and the higher TDG values during times of non-spill discharge (i.e., <1104 m 3 /s) post-modification. Although turbines can remove gas from supersaturated water [46], depending on how they are operated (e.g., how much water is passed through), air can be entrained, and TDG saturation increased above incoming values [47][48][49][50]. River discharge on either side of the spring hydrograph peak is representative of times when turbines can be operated in multiple combinations, and it is possible that turbine operations post-modification are the cause for these higher TDG values. ...
When water is spilled over dams, atmospheric gases can become entrained, resulting in supersaturated water. Total dissolved gas (TDG) > 110% saturation can cause gas bubble trauma (GBT) in fish. The negative effects of GBT include increased buoyancy, decreased swimming performance, and possible mortality. The lower Clark Fork River (LCFR) in Idaho frequently has TDG > 110% saturation due to the spill at Cabinet Gorge Dam as well as from upstream facilities. Spillway crests on Cabinet Gorge Dam were modified to reduce TDG production and the potential harm from GBT. To evaluate the effectiveness of spillway crest modifications, relationships between river discharge and measured TDG were developed pre- and post-modification and used to calculate the predicted TDG in the LCFR pre- and post-modification under two spill season discharge scenarios. The predicted TDG for the scenarios was used with an established TDG-GBT relationship for the LCFR to estimate the expected GBT incidence. Generally, TDG was lower post-modification, and the discharge at which 110% and 120% saturation were exceeded increased by about 198 m³/s. Modification also reduced the number of days with elevated TDG. The lower TDG post-modification resulted in significant (p < 0.05) reductions in the probability of observing GBT. The modification of Cabinet Gorge Dam spillway crests reduced TDG production over a range of discharges and has resulted in improved conditions for fish downstream of the dam.
... It seems likely that this failure to detect a significant difference was the result of differences in the distribution of data (i.e., much more data) and the higher TDG values during times of non-spill discharge (i.e., <1104 m 3 /s) post-modification. Although turbines can remove gas from supersaturated water [46], depending on how they are operated (e.g., how much water is passed through), air can be entrained, and TDG saturation increased above incoming values [47][48][49][50]. River discharge on either side of the spring hydrograph peak is representative of times when turbines can be operated in multiple combinations, and it is possible that turbine operations post-modification are the cause for these higher TDG values. ...
When water is spilled over dams, atmospheric gasses can become entrained resulting in supersaturated water. When total dissolved gas (TDG) exceeds 110% saturation, gas bubble trauma (GBT) can result in fishes. Negative effects of GBT include increased buoyancy, decreased swimming performance, and possible mortality. The lower Clark Fork River in Idaho frequently has TDG levels > 110% saturation due to spill at Cabinet Gorge Dam. Five spillway crests on the dam were modified to reduce TDG production and the potential harm from GBT. To evaluate the effectiveness of the spillway crest modifications, relationships between total river discharge and measured TDG were developed pre- and post-modification. These relationships were used to calculate the predicted TDG in the lower Clark Fork River pre- and post-modification under median and 75th percentile spill season discharge scenarios. The predicted TDG for the scenarios was then used with an established TDG-GBT relationship for the lower Clark Fork River to estimate the expected GBT incidence pre- and post-modification. In general, TDG was less post-modification with the discharge at which 110% saturation was exceeded increasing by about 198 m3/s. Modification also reduced the number of days with TDG > 110% by 7 and 14 days for the median and 75th percentile scenarios respectively. The lower TDG post-modification resulted in significant reductions in the probability of observing GBT. The results indicate that the modification of Cabinet Gorge Dam spillway crests reduced TDG production over a range of discharges and has resulted in improved conditions for fishes downstream of the dam. Species with relatively high GBT incidence like non-native Rainbow Trout Oncorhychus mykiss and Brown Trout Salmo trutta and native Westslope Cutthrout Trout O. lewisi and Peamouth Mylocheilus caurinus are the most likely to benefit from the reduced TDG conditions.
Keywords: Behavior, Fisheries/Habitat, Physiology, Water Quality
