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Optimizing the hydro unit commitment (HUC) has the potential to increase water use efficiency. However, the large number of variables, along with some nonlinear and non-concave constraints, present a huge challenge to the efficient solution of the HUC problem. For hydropower stations including multiple power plants that have different hydraulic heads, the problem is even more difficult. In this paper, we address this complex HUC problem using a two-layer nested optimization method. First, the total load demand is allocated to each power plant using a novel distribution rate. Thus, in the outer layer, a cuckoo search algorithm optimizes the distribution rate and each unit's on/off status, while in the inner layer, the load demand of each plant is allocated to online units through dynamic programming. China's Gezhouba Hydropower Station is selected for a case study. It is shown that: (1) the optimized water consumption is, on average, 1.71% lower than that of actual operations; (2) the optimized status of units vary smoothly with fewer startup/shutdown events; and (3) the optimization performance in non-flood seasons is better than that in flood seasons. These findings verify that the two-layer nested optimization method is an effective means of solving HUC problems for hydropower stations including multiple hydro plants with different hydraulic heads. • Solving HUC problems of hydropower stations including multiple plants with different hydraulic heads. • A two-layer nested optimization method is used to solve the HUC problem. • Load allocated between different hydro plants using a novel distribution rate. [ABSTRACT FROM AUTHOR]

Construction of hydropower stations has been an important approach to meet China's increasing power demand, but the impact of construction of hydropower stations on river microbiota is not fully understood. To evaluate this, the microbial composition from 18 sampling sites in the downstream of Jinsha River of China, upstream and downstream of two completed and two under-construction hydropower stations, were analyzed using high-throughput 16S rRNA gene sequencing. Three independent samples from each site were analyzed. A total of 18,683 OTUs from 1,350 genera were identified at 97% sequence similarity. Our results showed that the completion of hydropower stations would significantly increase the relative abundances of Acidobacteria, Chlorobi, Chloroflexi, Cyanobacteria, Nitrospirae, and Planctomycetes, especially the relative abundance of Synechococcus dOTUs and thus increase the risk of algal blooms. PCA based on all KEGG pathways and the significantly different KEGG pathways showed the predicted metabolic characteristics of the water microbiota by PICRUSt in the activated hydropower station group were significant difference to the other groups. Results from canonical correspondence analysis showed that water temperature and dissolved oxygen had significant effects on microbiota composition. These results are important for assessing the impact of hydropower stations on river microbiota and their potential environmental risks. [ABSTRACT FROM AUTHOR]

[Display omitted] • We used the MaxEnt model and the kernel density algorithm to simulate ecologically suitable zones for Glyptosternum maculatum . • The primary ecologically suitable areas for G. maculatum are situated in Ngamring County, Saga County, and Mainling County, with a total area of 553.15 km2. • Flow accumulation, NDVI, and Bio4 are the main environmental factors affecting the distribution of Glyptosternum maculatum . • Considering the ongoing impacts of factors such as hydropower stations and climate conditions, the projected suitable habitat area for G. maculatum is expected to span between 433.90 and 516.23 km2, marking a forecasted decrease of approximately 6.68 to 21.56 %. Glyptosternum maculatum, predominantly found in the middle and upper reaches of the Yarlung Zangbo River (YR) and its tributaries, is a fish species accorded second-class national protection. In 2021, it was recognized as one of the top ten excellent aquatic germplasm resources in China. However, its living conditions are far from promising. Therefore, in this study, we used the MaxEnt model to simulate potentially suitable habitat for G. maculatum , and then reconstructed the ecologically suitable habitat for G. maculatum using the kernel density algorithm after taking into account the distribution characteristics of hydropower stations. We predicted changes in area of the ecologically suitable habitat for G. maculatum under future climate change scenarios. The results indicate that the primary ecologically suitable areas for G. maculatum are situated in Ngamring County, Saga County, and Mainling County, covering a total area of 553.15 km2. Flow accumulation, NDVI, and the seasonality of temperature change are the main environmental factors affecting the distribution of G. maculatum . In the future, considering the ongoing impacts of factors such as hydropower stations and climate conditions, the projected suitable habitat area for G. maculatum is expected to span between 433.90 and 516.23 km2, marking a forecasted decrease of approximately 6.68 to 21.56 %. To prevent further reduction of suitable habitat, protective measures should be taken as early as possible. [ABSTRACT FROM AUTHOR]

Huang, X.; Suwal, N.; Fan, J.; Pandey, K., and Jia, Y., 2019. Hydrological alteration assessment by histogram comparison approach: A case study of Erdu River Basin, China. In: Guido-Aldana, P.A. and Mulahasan, S. (eds.), Advances in Water Resources and Exploration. Journal of Coastal Research, Special Issue No. 93, pp. 139–145. Coconut Creek (Florida), ISSN 0749-0208. The Erdu River is a small river in Hunan Province. This paper studies the quantitative assessment of the hydrological alterations in the hydrological regimes of the Erdu River caused by the Liujiaping hydropower station. Diurnal streamflow data between the time intervals from 1967-2013 were obtained from the Hengbanqiao station. The histogram comparison approach (HCA) and improved overall degree of hydrological alteration with new classification were used for the assessment. The hydrologic regime alteration was computed by the IHA (indicator of hydrological alteration) indices. As per the improved classification, three indices were altered at low degrees, seven -indices were altered at moderate degrees, eleven indices were altered at high degree and ten indices were altered at severe degree. The overall and improved overall degree of hydrological alteration for the Hengbanqiao station is 72% and 80.49% respectively, suggesting a high and severe degree of alteration respectively. The alteration degree of every IHA indices ranged from 32.29% to 100%. This shows that the current operation mode of Liujiaping hydropower station has severely deteriorated eco-hydrological regimes of the downstream area. Hence, there is an immediate need to operate the reservoir taking into consideration the ecological needs of the downstream areas, in order to preserve the river-ecology of the Erdu River. [ABSTRACT FROM AUTHOR]

• A new method of online, real-time prediction of downstream water levels is posed. • The Gezhouba Hydropower Plant in China is used as a reregulation case study. • A back propagation neural network-based prediction model is utilized. • Model water level predictions could fully meet real-time station dispatching needs. The forecasting accuracy of downstream water levels greatly impacts the economic operation of reregulating hydropower stations. If present, large errors in water level forecasting may require the hydropower station to discard water, which decreases the revenue from hydropower generation. Especially when the reregulating hydropower station undertakes the task of peak load regulation of the power grid, its power output may change drastically over a short period of time. Such large changes in the discharged flow of the hydropower station may inevitably cause an unsteady flow, which can lead to large fluctuations in the water levels of downstream rivers. In this case, the current forecasting methods, such as standard rating curves and empirical formulae, may inevitably result in large deviations when forecasting the change in the downstream water level. In order to reduce the volume of water discarded as a result of forecasting errors, a back propagation neural network-based forecasting model for downstream water levels of a reregulating hydropower station was constructed. The model enabled the direct, accurate, real-time forecasting of changes in downstream water levels by using measurable operation data from a hydropower station and process data on downstream water level changes. This method was applied to the actual hydropower generation dispatch of the Gezhouba Hydropower Plant in China. The results showed that as the peak load regulation volume increased, the forecasting errors of two conventional methods (standard rating curves and empirical formulae) became continuously superimposed. However, the water level forecasting error of the neural network-based method was small and could fully meet the real-time dispatching requirements of the hydropower station. In particular, under large peak load regulations, the maximum absolute values of the forecasting errors of the two conventional methods were close to 1 m, while that of the neural network-based method could be controlled within 0.3 m. [ABSTRACT FROM AUTHOR]

The Erdu River is a small river in Hunan Province. This paper studies the quantitative assessment of the hydrological alterations in the hydrological regimes of the Erdu River caused by the Liujiaping hydropower station. Diurnal streamflow data between the time intervals from 1967-2013 were obtained from the Hengbanqiao station. The histogram comparison approach (HCA) and improved overall degree of hydrological alteration with new classification were used for the assessment. The hydrologic regime alteration was computed by the IHA (indicator of hydrological alteration) indices. As per the improved classification, three indices were altered at low degrees, seven -indices were altered at moderate degrees, eleven indices were altered at high degree and ten indices were altered at severe degree. The overall and improved overall degree of hydrological alteration for the Hengbanqiao station is 72% and 80.49% respectively, suggesting a high and severe degree of alteration respectively. The alteration degree of every IHA indices ranged from 32.29% to 100%. This shows that the current operation mode of Liujiaping hydropower station has severely deteriorated eco-hydrological regimes of the downstream area. Hence, there is an immediate need to operate the reservoir taking into consideration the ecological needs of the downstream areas, in order to preserve the river-ecology of the Erdu River. [ABSTRACT FROM AUTHOR]

• Two site-groups were classified, corresponding to upstream-tributaries and mid-downstream. • Altitude and the proportion of substrate composition were major environmental variables influencing the spatial patterns of fish assemblages. • Compared with natural riverine conditions, reservoirs and dams seemed to affect fish communities to a small extent. • To protect the fish diversity of Anning River, construction of hydropower stations and sand extraction activities should be managed. In order to explore the spatial layout of fish assemblages and their related environmental factors, a survey of species composition was conducted in the Anning River. From 2018 to 2021, 28 sites at 987–2,077 m in altitude were surveyed, gathering 64 species in total, of which 60 were native and 4 were exotic. Fifteen of the species sampled were indigenous to the upper Yangtze River, and two were classified as critically endangered or endangered. Fish communities displayed significant upstream-to-downstream variation. There are two site-groups, one covering upstream and tributaries and the other covering midstream and downstream. The upstream-tributary fish assemblages had a dominance of Nemacheilidae and Schizothoracinae, which are plateau species with habitat preferences for boulders and fast-flowing water. Conversely, the mid-downstream fish assemblages had a dominance of Gobioninae, Cyprininae, Bagridae and Siluridae, which are common river species that prefer slow-flowing water. The spatial patterns of these fish communities were chiefly affected by altitude and substratum composition. The fish assemblage pattern was consistent with the zonation concept because the fish communities changed abruptly and clearly along the upstream–downstream axis. The findings of this study offer a crucial research foundation for comprehending the fish assemblages of mountainous rivers, which will be conducive to biodiversity management and habitat preservation of aquatic species. [ABSTRACT FROM AUTHOR]

The current development trend of China's hydropower is moving toward ultra-high heads, complex geological scenarios, ultra-large capacities, and the Tibetan region. The construction of hydropower stations with super-long headrace tunnels is conducive to overcoming the constraints of complex geological conditions and making full use of hydropower resources. However, these stations have unique technical problems that limit their commercial development, including pressure fluctuations during load rejection and the operational stability of the power-frequency regulation. In this study, a potential problem in hydropower stations with super-long headrace tunnels, the instability during load acceptance, is studied by combining prototype experiments with 1D transient numerical simulations. First, according to a test case using a prototype hydropower station, the instability phenomenon occurring during a simultaneous load acceptance of two Francis turbines in a hydropower station with a 20-km headrace tunnel is described. Next, using 1D steady-state and transient simulations, the factors leading to the instability are analyzed in detail. Finally, countermeasures for the safe operation of hydropower stations are proposed based on numerical simulations and supplementary prototype experiments. Hydropower stations with super-long headrace tunnels exhibit a characteristic where the net head decreases sharply with an increase in the flow rate. Therefore, prior to load acceptance, the maximum output achievable by the multiple units under the operating net head has to be carefully determined to avoid over-adjustment of the guide vane opening and detrimental phenomena such as operational instability and extremely low pressure in the draft tube. • Instability of a hydropower station with a super-long headrace tunnel has been discovered. • This instability has been reasonably simulated by one-dimensional transient simulation. • The effect of a super-long headrace tunnel on the operational instability has been revealed. • Countermeasures for the safe operation are proposed. [ABSTRACT FROM AUTHOR]

Complex block-flexure slope toppling is observed in interbedded sandstone and slate in the upper Yellow River, China. Block toppling is observed in the relatively hard sandstone and flexural toppling is observed in the relatively soft slate. The evolution of toppling slope deformation is characterized by long-term progress and spatial variability. In order to study these characteristics, field investigations, adit prospecting, borehole drilling, sonic tests and numerical simulation were carried out. In addition, the effect of the structure, the composite mode of the rock mass, the unloading fissures and geomorphology are discussed. Furthermore, we explored the toppling mechanisms and simulated it numerically; on this basis, the slope evolution is divided into four stages. Results obtained from the numerical simulation compared well with field investigation data (investigation data, rock sonic survey and strata dip statistics). Comparative studies have demonstrated that the analytical methods presented in this paper are appropriate for back analysis of the toppling evolution process. The result showed that this toppling slope has not yet entered the later progressivity failure stage and is currently limited to collapse at shallow levels, whereas the deep-seated rock mass will remain stable for a long time. This study might provide reference for a stability evaluation and hazard prevention analysis for rock toppling. [ABSTRACT FROM AUTHOR]

The paper deals with a development of a new procedure to perform probabilistic block theory analysis using the vector method. The procedure includes the following three main features: (a) the joint orientation is considered as a bivariate distribution including the correlation that exists between the joint dip angle and dip direction angle; (b) the variability of discontinuity shear strength is incorporated in the analysis; (c) it performs deterministic and probabilistic block theory analysis including the mode of failure (MOF), maximum safe slope angle (MSSA), factor of safety (F S ) and the instability probabilities for different cut slope dip angles (CSDA) and different MOFs. A rock slope at a hydropower station in China is used as a case study to illustrate the use of the developed procedure. The slope has six sets of discontinuities. Therefore, both deterministic and probabilistic block theory analyses were conducted for 4-plane, 5-plane, 6-plane and 7-plane blocks to study the stability of the rock slope under different MOFs and CSDA. For most MOFs, the MSSA obtained through deterministic analysis were found to be significantly higher than the CSDA obtained corresponding to zero instability cumulative probability. The differences obtained between the deterministic and probabilistic analyses resulted mainly due to the variability of discontinuity orientation. The case study illustrated the importance and superiority of the probabilistic analysis over the deterministic analysis. For the investigated rock slope by selecting the CSDA of 40° and 50°, the total instability cumulative probability can be limited to less than 5% and 10%, respectively. [ABSTRACT FROM AUTHOR]

Huang, X.; Suwal, N.; Fan, J.; Pandey, K., and Jia, Y., 2019. Hydrological alteration assessment by histogram comparison approach: A case study of Erdu River Basin, China. In: Guido-Aldana, P.A. and Mulahasan, S. (eds.), Advances in Water Resources and Exploration. Journal of Coastal Research, Special Issue No. 93, pp. 139–145. Coconut Creek (Florida), ISSN 0749-0208. The Erdu River is a small river in Hunan Province. This paper studies the quantitative assessment of the hydrological alterations in the hydrological regimes of the Erdu River caused by the Liujiaping hydropower station. Diurnal streamflow data between the time intervals from 1967-2013 were obtained from the Hengbanqiao station. The histogram comparison approach (HCA) and improved overall degree of hydrological alteration with new classification were used for the assessment. The hydrologic regime alteration was computed by the IHA (indicator of hydrological alteration) indices. As per the improved classification, three indices were altered at low degrees, seven -indices were altered at moderate degrees, eleven indices were altered at high degree and ten indices were altered at severe degree. The overall and improved overall degree of hydrological alteration for the Hengbanqiao station is 72% and 80.49% respectively, suggesting a high and severe degree of alteration respectively. The alteration degree of every IHA indices ranged from 32.29% to 100%. This shows that the current operation mode of Liujiaping hydropower station has severely deteriorated eco-hydrological regimes of the downstream area. Hence, there is an immediate need to operate the reservoir taking into consideration the ecological needs of the downstream areas, in order to preserve the river-ecology of the Erdu River. [ABSTRACT FROM AUTHOR]

The cofferdam built at the inlet of the diversion tunnel may be left due to incomplete blasting demolition, which affects the river closure. Several indexes have been used to evaluate the difficulty of river closure, but all indexes suffer from their limitations in use. Thus, it is more useful to combination multiple indexes to analyze the impact of residual cofferdam. Taking the river closure project of a Hydropower Station in southwest China as an example, the influence of the residual cofferdam heights on the river closure was studied by experiments. The discharge of river closure is 590 m3/s and 758 m3/s. In this paper, the results of studies on a 1:50 scale hydraulic model based on the Froude similitude relationships are presented. The test results show that the discharge capacity of the diversion tunnel is reduced by 27.2% at most when this height is more than 2 m. The residual height mainly affects the maximum of stream energy with unit width, which increase by more than 50% at most compare to Non-existent residual cofferdam. However, the final drop, max-velocity along the gap axis, the local scour of riverbed and the flow pattern of the gap are basically not affected. In addition, with the height increase, the bank collapse is intensified, and the amount of dumped material with medium size increases, especially when it reaches 4 m, the large or Extra-large size stones begin to be dumped. Based on the comprehensive evaluation of multiple indexes and the type of dumped material, it is shown that the residual cofferdam height more than a certain value, the value is 2 m for the case study, will significantly increase the river closure difficult. [ABSTRACT FROM AUTHOR]

Laxiwa Hydropower Station is the largest among those hydropower stations in the upper reaches of the Yellow River. The construction started in October 2001, diversion tunnel was finished in January 2004, and impoundment started in March 2009. However, from May 2009, the right-bank slope of the reservoir about 700 m high and 1,000 m wide located 500 m far from the dam was found to be deforming greatly and continuously. Although this slope had been identified as an old landslide, the survey before the construction of the dam concluded that this slope being composed of granite is stable and would be stable even after the impoundment, and thus no detailed monitoring of the slope deformation had been performed before the visible deformation occurred after the impoundment. To indentify the relationship between the deformation of the slope and impoundment, we utilized differential synthetic aperture radar interferometry and Advanced Land Observing Satellite Prism data to analyze the slope deformation before and after impoundment. We found that no identifiable deformation took place before the impoundment, while during the period of 3 April 2009 to 22 May 2010, after impoundment, maximum horizontal displacement reached approximately 7.5 m. This slope is still deforming even after a total horizontal displacement of several tens of meters being reached, showing high risk of catastrophic failure. [ABSTRACT FROM AUTHOR]

Abstract: The heat and moisture environment of hydropower stations underground plants will directly affect the useful life and safe running of electromechanical devices. Engineers need to calculate the transient heat and moisture loads due to the storage and transport of heat and moisture in the porous cavern envelopes. In order to avoid complex dynamic calculations and save design time, this paper gives monthly mean hygrothermal absorption and desorption indexes and regression formulas of limestone envelopes with no-lining. These indexes are obtained by means of numerical calculation method based on the air temperature and moisture fluctuation ranges controlled by air-conditioning systems and hygrothermal parameters of cavern envelop. And then, validity and reliability of hygrothermal absorption and desorption indexes are verified by using monitored data of main plants in Dachaoshan and Jiangkou hydropower stations in China. The results show that the heat and moisture indexes can be applied in real project design and operation management. [ABSTRACT FROM AUTHOR]

Unsteady flow induced by hydropower stations exerts a significant impact on the water level in multi-approach channels, which directly threatens the safe passage of ships. In this study, a one-dimensional and a two-dimensional hydrodynamic model are adopted to simulate the water level fluctuations at the entrance of multi-approach channels and the lower lock head of a ship lift with consideration of initial water surface elevation, base flow, flow amplitude, regulation time, and locations of hydropower stations, unfavorable conditions are successfully identified; and the fluctuations at the approach channel entrance and the lower lock head of a ship lift under single-peak and double-peak regulating mode are analyzed considering the flow regulating of the Gezhouba Hydropower Station (GHS), thus, the water level oscillation process in the multi-approach channels is presented. Results show that the largest wave amplitude in the multi-approach channels manifests under unfavorable conditions including lower initial water surface elevation, smaller base flow, larger flow variation, and shorter regulation time; and water level fluctuation in the multi-approach channel is primarily induced by flow amplitude and net flow between the Three Gorges Hydropower Station (TGHS) and the GHS, with consideration of the counter-regulation process of the GHS. This research contributes to providing a reference for a similar large-scale cascade hydropower station regarding regulation and control of navigation conditions. [ABSTRACT FROM AUTHOR]