Influence of Operational Timing on the Efficiency of Venting Turbidity Currents

Reservoir sedimentation is gaining growing attention as dams are aging, due to economic and environmental consequences. Venting of turbidity currents is one of many sediment management techniques, highly recommended when water is in shortage. The venting operation is experimentally investigated using two reservoir bed slopes. The main research questions concern the opening timing of bottom outlets and the duration of venting. The timings tested are relative to the arrival of the current at the outlet. The results showed that in-time venting, synchronized with the arrival of the turbidity current at the outlet, is more efficient than early or late venting. It is recommended to start opening the gates when the turbidity current is around 300 m upstream of the outlet, so that the evacuation is synchronized with the arrival of the current at the dam. Additionally, venting should not be stopped immediately after the end of the turbidity current flow but should instead last for a certain time in order to evacuate the muddy lake depending on the outflow discharge

Baseline Cytomegalovirus Viremia at Cryptococcal Meningitis Diagnosis Is Associated With Long-term Increased Incident TB Disease and Mortality in a Prospective Cohort of Ugandan Adults With HIV.

BACKGROUND: Adults with HIV-associated cryptococcal meningitis have overlapping burdens of cytomegalovirus (CMV) and tuberculosis (TB) coinfections. CMV infection/reactivation is strongly associated with CMV-specific memory T-cell activation and upregulation of type 1 interferons, which may lead to increased risk of TB disease and poor outcomes. METHODS: We conducted a cohort study of 2-week survivors of cryptococcal meningitis during 2010-2021 to determine TB incidence and all-cause mortality over time stratified by baseline CMV status. RESULTS: We followed 497 Ugandans with HIV-associated cryptococcal meningitis for a median (interquartile range) of 4.6 (2.6-53.9) months. Overall, 42% (210/497) developed incident TB disease or died. One-fifth (98/497, 19.7%) developed incident TB disease, and 29% (142/497) of participants died during follow-up. Of 259 participants with CMV viral load measured at baseline, 37% (96/259) had concurrent CMV viremia (defined as anyone with detectable CMV DNA in plasma/serum by qualitative polymerase chain reaction [PCR] detection). Of 59 with measured CMV immunoglobulin G (IgG), 100% had positive CMV IgG antibody serology (≥10 enzyme-linked immunosorbent assay units/mL). CMV viremia was positively associated with higher HIV viral load (196 667 vs 73 295 copies/mL; P = .002) and higher cerebrospinal fluid fungal burden (68 500 vs 14 000 cfu/mL; P = .002) compared with those without. Participants with high-level CMV viremia (defined as CMV viral load ≥1000 IU/mL) had twice the risk of incident TB (subdistribution adjusted hazard ratio [aHR], 2.18; 95% CI, 1.11-4.27) and death (aHR, 1.99; 95% CI, 1.14-3.49) compared with participants with no or low-level CMV viremia. There was no association between the CMV IgG index and the incidence of TB/death (P = .75). CONCLUSIONS: CMV viremia >1000 IU/mL at meningitis diagnosis was associated with increased incident TB disease and mortality during long-term follow-up. Future studies to determine the causal relationship and potential for therapeutic intervention are warranted

Numerical Simulations of an Innovative Water Stirring Device for Fine Sediment Release: The Case Study of the Future Trift Reservoir

Reservoir sedimentation and consequently lack of storage volume and perturbation of the operation of intakes and bottom outlet is a key challenge affecting both hydropower production as well as dam safety and flood management. In the framework of a peer-reviewed research project (Jenzer-Althaus, 2011) an innovative countermeasure, called SEDMIX, was proposed allowing to keep in suspension or re-suspend the fine particles near the power water intakes, thanks to an optimized arrangement of four water jets producing an upward whirling flow like produced by a mixer. With such a system, the suspended particles can be conveyed downstream at acceptable rates through the power waterways during the normal operation of the hydropower plant. Although experimental studies have shown the very promising efficiency of such a device in simple cases and by numerical simulations in a laboratory reservoir, SEDMIX performance has not been investigated yet in a real-life reservoir under prototype conditions. The aim of this study is therefore, to analyze the performance of a real-sized SEDMIX operating in the future Trift reservoir via numerical analyses. This study allows to validate or to improve SEDMIX optimal configuration experimentally determined. The numerical simulations are performed for different positions and heights for the SEDMIX device. The performance of SEDMIX in each position has been evaluated and tested for different jet discharges. The analysis of the numerical simulation results shows that the presence of SEDMIX does create a vortex flow pattern and sediment movement upward. The sediment volume fraction in the higher layers of the reservoir increases and consequently the evacuated volume of fin sediments increases for simulation using the SEDMIX device comparing those without the device

Projecting hydropower production under future climates: a guide for decision‐makers and modelers to interpret and design climate change impact assessments

Hydropower is a key energy source in almost all world regions. It fuels social and economic development, ensures electricity security, and is a pillar for renewable electricity production. But hydropower and its environmental impacts are vulnerable to climate change. This discussion of model-based climate change impact assessments and underlying modeling assumptions will help decision-makers and scientists analyzing existing studies and identifying the most urgent open questions. Rooted in hydrological uncertainty analysis, this discussion focuses on the importance of local factors and on modeling uncertainties for a critical view on our ability to project future hydropower production in different world regions. (C) 2015 Wiley Periodicals, Inc