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A numerical model of a hydraulic system with a closed surge tank is developed for evaluating the thermodynamic behavior during slow transients in the air pocket. The numerical model is used to evaluate the polytrophic equation against a Modified Rational Heat Transfer (MRHT) method, and the results are compared to field observations. The original RHT method considers heat transfer to walls and water as a lumped quantity, and the method is modified in this work to evaluate these two processes separately. The field observation dataset contains pressure and water level measurements from a 3,050 m3 closed surge tank during a pressure increase from 805 to 1543 kPa over 40 min, thus providing a unique opportunity to investigate the thermodynamic behavior during slow transients. This paper will show how the accuracy of modeling slow transient events in a closed surge tank may be improved by applying the MRHT method, which accounts for heat transfer to enclosing media. [ABSTRACT FROM AUTHOR]

Pressure reducing valves (PRVs) are often used to manage pressure and reduce losses in water distribution systems (WDS). Different approaches are available in the literature on how to locate and set the PRVs in order to maximize their effectiveness and minimize water losses. The available methodologies minimize the mean square difference between the actual and the target pressure at each node. Since the excess head can be used also to generate hydropower by using turbines and/or pumps as turbines (PATs), a different objective function could be suggested to maximize energy production. Consequently, a comprehensive analysis will be developed in the paper which highlights the differences between the preexisting approach and the suggested one, in terms of device location, pressure reduction, and recoverable energy. Numerical simulations showed that minimizing pressure may also affect the production of energy, while maximizing the energy production itself could be an attractive alternative, leading to higher generation and only a slight increase of the average node pressure. [ABSTRACT FROM AUTHOR]

Even after a century of development, the total hydropower potential from undeveloped rivers is still considered to be abundant in the United States. However, unlike evaluating hydropower potential at existing hydropower plants or nonpowered dams, locating a feasible new hydropower plant involves many unknowns; hence, the total undeveloped potential is harder to quantify. In light of the rapid development of multiple national geospatial data sets for topography, hydrology, and environmental characteristics, a merit matrix-based geospatial algorithm is proposed to identify possible hydropower stream reaches for future development. These hydropower stream reaches-sections of natural streams with suitable head, flow, and slope for possible future development-are identified and compared by using three different scenarios. A case study was conducted in the Alabama-Coosa-Tallapoosa and Apalachicola-Chattahoochee-Flint hydrologic subregions. It was found that a merit matrix-based algorithm, which is based on the product of hydraulic head, annual mean flow, and average channel slope, can effectively identify stream reaches with high power density and small surface inundation. These identified stream reaches can then be evaluated for their potential environmental impact, land development cost, and other competing water usage in detailed feasibility studies. Given that the selected data sets are available nationally (at least within the conterminous U.S.), the proposed methodology will have wide applicability across the country. [ABSTRACT FROM AUTHOR]

A multiobjective model with chance constraints is proposed to obtain hedging rules for hydropower reservoirs based on initial reservoir operating rules derived using stochastic dynamic programming. In the model, hedging rules are evaluated through simulations and the maximizations of minimum powers in simulation horizon of hydropower reservoirs are taken as objectives. The maximum-minimum objectives are substituted by aggregated functions. A genetic algorithm is used to solve the model, with a fuzzy optimal method evaluating the individuals. A case study shows that the proposed approach is feasible and efficient to produce a series of hedging rules with different reliability levels, and valuable to balance the magnitudes of generation below firm power and the chances of such events. [ABSTRACT FROM AUTHOR]

The use of microhydroelectric plants in urban pipe networks, based on the combination of a pump as turbine (PAT), two regulating valves, and two pressure meters, is proposed along with simple automation rules. Its economic benefit is tested on a small pipe network, where the network geometry as well as the demand coefficient variation in time and space have been inferred from previously collected data and existing analysis. A similar analysis has been also carried out for different scenarios in which the reduction of pipe installation cost due to a diameter reduction is compared with the increased benefit in energy production. The case study shows that a small increment of the pipe installation cost, with respect to the minimum required by the nodes minimum pressure, can lead to a larger benefit for energy production. [ABSTRACT FROM AUTHOR]

This paper addresses a knowledge-based approach for reservoir system optimization. The approach takes a more detailed consideration of each turbine in a hydropower plant than the traditional constant output coefficient method. To use this approach, a knowledge expression and a knowledge function are defined for hydropower plant operation. The knowledge expression is extracted by dynamic programming to save all possibly optimal situations of unit commitment, and further, the knowledge function is formulated based on a two-dimensional interpolation of the knowledge expression. Through the use of the knowledge expression and the knowledge function, computer memory requirements can be reduced and unnecessary computations can be avoided in the reservoir operation optimization. To overcome the decomposition schemes in time and in space and guarantee finding the global optimum (in a discrete sense) with an extended time horizon, up to 400 CPU cores are used to run a parallel dynamic programming model, which applies the knowledge-based approach, to estimate the maximum energy production of the Three Gorges Project (TGP) and the Gezhouba Project (GZB) cascade hydropower plants in China in the year of 2010, with 1 day as the time step and 365 days as the time horizon. The case study results show that the maximum energy production of the TGP-GZB system would be in 2010 under the current operating rules. Thus, there is still room for improvement in energy production, with the maximum increase of 1.83% () from optimizing hydropower plant operation and 3.46% () from optimizing both hydropower plant operation and reservoir operation. The overall approach is effective in providing optimal assessment solutions with an acceptable computation time. Thus, it can be concluded that the approach can be applied for planning purposes or providing more reasonable boundaries for real-time operation. [ABSTRACT FROM AUTHOR]

Water systems in snowmelt-dominated hydroregions such as California's Sierra Nevada mountains are sensitive to regional climate change, hydropower systems in particular. In this study, a water resources management model was developed for the upper west slope Sierra Nevada to understand the potential effects of regional climate warming on hydropower at the watershed scale, a scale that has been largely neglected but is important for hydroregional planning. The model is developed with the Water Evaluation and Planning system (WEAP) and includes most water management infrastructure in the study region. Hydropower is simulated assuming historical long-term electricity demand and a spill minimization rule. The method is suitable for simulating generation for most of the main watersheds in the region. To assess the potential effect of climate warming, uniform air temperature increases of 0°C, 2°C, 4°C, and 6°C were considered, with no change in precipitation, to approximate regional warming through 2100. The highly productive northern Sierra Nevada sees large reductions in hydropower generation with decreases in annual runoff. The central watersheds see less reduction in annual runoff and can adapt better to changes in runoff timing. Generation in southern watersheds, which are less productive, decreases. Results from this study can help identify which watersheds might easily adapt to climate change, where hydropower is likely to conflict with other uses, and where more detailed operational studies are needed. [ABSTRACT FROM AUTHOR]

In recent decades, there has been a rapid rate of development of hydropower in China. The unprecedented rate of expansion, development scale, and large numbers of hydropower plants have posed a challenge to the operation of large-scale cascaded hydropower systems (OLCHSs), which has become one of the most important factors in ensuring the security and economic operation of the power grid in China. In this paper, a long-term optimal operation model is developed for the purpose of maximizing the total generated energy of cascaded hydropower plants. To solve the OLCHS problem effectively, an elite-guide particle swarm optimization (EGPSO) algorithm is proposed in this paper. An external archive set, which can preserve elite solutions during the evolution process, is employed to provide flying directions for particles. Since the OLCHS problem is a high-dimensional, nonlinear, multistage, and stringent constraint optimal problem, the proposed algorithm introduces three new innovations: a layer-partition approach is presented to divide the decision vectors into small ones according to the reservoir's relative position and hydraulic connection. Meanwhile, the initial solutions are generated in the proposed contractively feasible region so that operation results do not rely so much on the initial solution. To deal with the multiconstraint coupling problem, a constraint-corridor method is adapted to handle these complex constraints in the cascaded hydropower system. Finally, this novel strategy is applied successfully to solve the optimal operation of a large-scaled cascaded hydropower system in the upper reaches of the Yangtze River. Compared with the conventional method, the proposed EGPSO has a competitive performance in not only simulation results but also computing time, which offers a new approach to solving high-dimensional and complicated problems of optimizing reservoir dispatching. [ABSTRACT FROM AUTHOR]

Tools for engineers who assess and optimize hydropower intakes are provided to help them measure and quantify the characteristics of free surface vortices (characteristic radius, bulk circulation, tip depth, nominal depression slope) that form at the intakes. Accessible methods are proposed for measuring and modelling vortex characteristics and the processes that affect their generation and strength. Common mechanisms that produce and strengthen the vortices (flow separation, shear, asymmetric approach flow) are discussed. An analytical model, based on Burgers's vortex model and laboratory measurements, is described that incorporates the effect of the approach flow and intake geometry on vortex characteristics. Simple measurement techniques (acoustic Doppler velocimetry and surface particle tracking velocimetry) are presented by which the flow and vortex characteristics can be documented, allowing the model to be adjusted to the particularities of the specific intake under consideration. The analytical model is then used to help understand how the different processes affect the scaling of vortex characteristics. [ABSTRACT FROM AUTHOR]

Following three decades of rather low investment in dams, many regions throughout the world are now seeking to further develop new storage capacity to meet exploding demands for water and to hedge against the risk posed by climate change. Storage capacity is often perceived as a key element of climate change adaptation strategies, while at the same time contributing to socioeconomic development through irrigation, energy generation, fish production, and municipal and industrial water supply. The benefits provided by dams must be balanced with the associated environmental and social costs, which can take various forms, such as the degradation of ecosystems because of altered flow regimes and the relocation of people from the impoundment area. The benefits of storage essentially come from the ability to move water in time, making it available during the low-flow season when it becomes more valuable. As river basins develop and new dams are constructed, it may be important for planning and operational purposes to assess the individual contribution of each reservoir to the benefits of storage. This paper presents a methodology to determine the economic value of storage in multireservoir systems based on the marginal net benefit functions of storage and on hydroeconomic modeling. A cascade of reservoirs in the Euphrates river basin is used to illustrate the methodology. [ABSTRACT FROM AUTHOR]

The writers propose a successive improved dynamic programming (SIDP) algorithm for hydropower reservoir operation based on an analysis of concavity, complementarity, and monotonicity of hydropower problems. For single-period hydropower generation, storage and release have diminishing marginal contributions to hydropower generation (i.e., concavity), and there is also a complementary effect between storage and release (i.e., release becomes more productive in accordance with increasing storage). For multiple-period hydropower generation, the complementarity influences the concavity of the objective function and the monotonicity of operation decisions, and is the major cause of complexity in hydropower operation. With mathematical derivations, the writers propose a concave approximation to the hydropower generation function and a SIDP algorithm for hydropower reservoir operation. The efficiency of SIDP is demonstrated with two hypothetical case studies of long-term hydropower scheduling, which shows that the computation time of SIDP increases linearly in accordance with the number of storage intervals [i.e., ], whereas dynamic programming (DP) shows a quadratic increase [i.e., ]. [ABSTRACT FROM AUTHOR]

Global climate change is expected to lead to changes in precipitation patterns and increased frequency and intensity of extreme weather events, which may produce conditions outside current design criteria for dams. This study investigated climate change effects on future safety of the Aurland hydropower dams during extreme floods. The design inflow floods for present and future climate scenarios were calculated using two approaches. Flood frequency analysis was applied to the annual maximum series from the simulated daily flows for present and future periods. Analysis of extreme precipitation and floods was performed using a hydrological model to compute the corresponding extreme flood values for the present situation and future scenarios. The outflow flood with the associated water level was calculated using a reservoir routing model linking all the Aurland reservoirs. In this paper, the authors present current and future design floods for the Aurland case and the implications of the changes in flood levels on dam safety for single reservoirs and for the reservoir system as a whole. Results from this study show that there will be a change in seasonal shift in the peak inflow flood from summer to autumn for the future scenario; from the range of results of the climate models and emission scenarios, the design inflow flood and the probable maximum flood (PMF) in the autumn is projected to increase for the future scenario. [ABSTRACT FROM AUTHOR]

Hydroreservoirs usually serve two main purposes: hydropower production and water consumption. The great flexibility, low operating costs, and low carbon impact of hydroturbines turns them into a desirable technology in the generator mix of power systems. In addition, sustainability and environmental concerns support their use in current power systems, along with other renewable energy sources like wind and solar energy. However, the stochastic nature of river inflows hinders their long-term use and hints at the need to use planning tools. Furthermore, it also requires the use of planning tools in order to balance present and future requirements. This work presents a simulation tool that is employed at Iberdrola to help in the preparation of medium-term hydroelectric production schedules. The main objective of the simulation is to follow the production guidelines given by a long-term hydrothermal problem, while avoiding spillages and failures to fulfill water release agreements. In order to achieve this, the simulation algorithm is structured around several phases that aim at coordinating the operation of all the elements in the basin. This way, the simulation tool provides the operator a way to evaluate the outcome from forecasts of either water inflows or future operation situations. Some of the potential applications of this simulation tool are shown in this work: general simulation in order to know in advance the consequences of possible inflow forecasts, and how to assess several maintenance schedules and different upgrade plans. [ABSTRACT FROM AUTHOR]

This paper presents a methodology for obtaining and adjusting of efficiency curves for hydroelectric generating units. It is based on measured data of power, gross head, and water discharge recorded by the company that manages the plant operation. The objective is to determine the actual performance characteristics of the set: turbine, generator, and penstock. In order to obtain the efficiency functions, an iterative calculation is used. Its input data are the functions currently in use of turbine efficiency, generator efficiency, and penstock head losses. For the adjustment of the efficiency functions, the Generalized Reduced Gradient optimization method is employed. A case study was applied to the data from a large Brazilian hydroelectric plant whose operation is under the coordination of the Electric System National Operator. The benefits of the proposed methodology are analyzed using a simulation tool for the hydroelectric operation. The simulator is used to reproduce the past operation of the plant, first with current data and second with adjusted data. The results show that the optimal unit efficiency functions significantly contribute to bring the real and simulated operation closer. [ABSTRACT FROM AUTHOR]

The Mekong River supports unique biodiversity and provides food security for over 60 million people in the Indo-Burma region, yet potential changes to natural flow patterns from hydropower development are a major risk to the well-being of this system. Of particular concern is the ongoing and future development of 42 dams in the transboundary Srepok, Sesan and Sekong (3S) basin, which contributes up to 20% of the Mekong's annual flows and provides critical ecosystem services to the downstream Tonle Sap Lake and the Mekong Delta. To assess the magnitude of potential changes, daily flows were simulated over 20 years using the HEC ResSim and SWAT models for a range of dam operations and development scenarios. A 63% increase in dry season flows and a 22% decrease in wet season flows at the outlet of the 3S basin could result from the potential development of new dams in the main 3S rivers under an operation scheme to maximize electricity production. Water-level changes in the Mekong River from this scenario are comparable with changes induced by the current development of Chinese dams in the Upper Mekong Basin and are significantly higher than potential flow changes from the proposed 11 mainstream dams in the Lower Mekong Basin. Dams on the upper sub-tributaries of the 3S basin have very little effect on seasonal flow regimes because most of those projects are run-of-the-river dams and have small reservoir storages. The effects on hourly flow changes resulting from intra-daily reservoir operations, sediment movement, water quality, and ecology require further study. Strategic site selection and coordinated reservoir operations among countries are necessary to achieve an acceptable level of development in the basin and to mitigate negative effects in seasonal flow patterns, which sustain downstream ecosystem productivity and livelihoods. [ABSTRACT FROM AUTHOR]

The middle-term and long-term runoff forecasting model of the hydropower station reservoir is established with the Bayesian statistic forecasting theory; uncertainty of the hydrological forecasting is quantitatively described in the form of a probability distribution to explore the statistic forecasting theory and its application value. The uncertainty of the input factor is processed with the forecasting model of grey correlation of meteorological factors, and real-time weather data are effectively combined with the historical hydrological data to break through the restriction of traditional deterministic forecasting methods in the aspects of information utilization and sample study to improve the precision of hydrological forecasting. The established model has been assessed by the example of the reservoir of the Fengman hydropower plant. It is indicated by the analog computation result that this model, compared with the deterministic runoff forecasting method, has advantages not only in quantitatively considering the uncertainty in decision making, but also in improving the precision of runoff forecasting in the expected significance, and has comparatively high application value. [ABSTRACT FROM AUTHOR]

Water hammer is an unsteady hydraulic problem commonly found in closed conduits of hydropower plants, water distribution networks, and liquid pipeline systems. Because of either a malfunction of a system or inadequate operation conditions, a pipeline may collapse or burst erratically, resulting in substantial damages and human loss in some cases. Therefore, it is crucial that engineers design and/or analyze projects with reliable computing methods for all foreseeable operation situations. In this paper, transient flow situations in run-of-river plants are investigated for various operation conditions such as load rejection, load acceptance, and instant load rejection. A computer program using the method of characteristics is used in two case studies having Pelton and Francis turbines, respectively. On the basis of the field data of the plants, their computational models are set up, and resulting transient pressures are computed and compared with available measured pressures. Comparisons indicate that the mathematical model predicts the measured pressures closely for all simulations. [ABSTRACT FROM AUTHOR]

Hydropower is a major power source in cold region countries. It is also the largest renewable energy source offering significant potential for reduction in carbon emissions. In Norway, hydropower accounts for nearly 99% of the total electricity production. To meet winter demand, storage schemes are implemented in tandem with run-of-river schemes to a large extent in cold region hydropower systems. In these systems, ice creates operational constraints during winter that can lead to reductions in power production. The problems occur in the various phases of the ice regime, mainly due to frazil ice, ice runs, and ice jams. Counteracting these ice problems is usually a difficult task that involves expensive measures and possibly lost production. This paper presents a comprehensive review of the effects of freshwater ice on hydropower systems. It has been shown that ice in freshwater systems poses a number of operational constraints on the various components of a hydropower system at a time when energy demand is at its peak. The literature review presents a useful baseline for operators of power plants as well as showing problem areas for future research. The trends in the northern areas toward warmer and unstable winters could both alleviate and exacerbate the current challenges for cold climate hydropower operation and the findings of this paper should provide useful background for assessments of future ice impacts. [ABSTRACT FROM AUTHOR]

Given the important role of hydropower in peak electricity management, Middle Eastern countries are actively pursuing development of more hydropower resources by construction of large dams. Nonetheless, climate change is expected to affect the future productivity of hydropower by influencing the hydrologic cycle and different climate variables in the region. Although reactive plans to minimize climate change impacts on hydropower production have been implemented in the developed world, the developing world can still benefit from proactive actions. Studies of climate change impacts before and during implementation of hydropower projects can result in timely responses and adaptation to climate change with a potential of considerable cost savings. This study investigates the potential impacts of climate change on the hydropower systems in the Karkheh River Basin-the third largest river basin in Iran-in terms of potential for hydroelectricity generation. A simulation model is developed to examine how hydropower generation levels vary for different future climate change scenarios in this representative Middle Eastern basin. The obtained results suggest that the existing operation rules and design specifications, developed based on the historical climatic conditions, can lead to inefficient operations of the hydropower in the basin. Because of insignificant streamflow reductions in the short term, hydropower production may not change considerably in the near future. However, a serious hydropower generation deficit is expected in the midterm and long-term horizons in the Karkheh River Basin. Therefore, adaptation to the future climate change conditions and revision of the operation rule curves and design specifications are essential to optimal hydropower operations in this basin. [ABSTRACT FROM AUTHOR]

Existing studies tend to agree that there are links between owners' capabilities and project performance. However, limited research has systematically addressed the relationships among the multiple facets of organizational capabilities and project performance. This paper quantitatively investigated the relationships among them by developing and testing a capability model. With support of data collected from the hydropower project industry in China, this study has revealed strong correlations between owners' capabilities and project performances, confirming owners' capabilities on obtaining scarce and valued resources, interorganizational linking, information management, and integrating and managing resources can have significant impacts on hydropower project performances. It is concluded that these owners' capabilities are not only important to improve project performances on quality, time, cost, and safety by maximizing the effectiveness of each participant's resources, but also critical to appropriately deal with hydropower projects' externalities for achieving the objectives on project migration, and ecological and environmental impacts. Future studies should be conducted to understand how owners can correctly perceive the properties of external environments for obtaining resources, and to successfully integrate and manage reciprocally interdependent project delivery processes at both intra- and interorganizational levels to achieve superior project performance. [ABSTRACT FROM AUTHOR]

In many watersheds around the world where the importance of assessing a watershed as a whole is overlooked, new water resources projects are designed solely based on historic flow data. Such projects might fail to operate satisfactorily when designed without considering the uncertainties associated with future hydrologic changes. In this study, a system dynamics model (SDM) is developed to quantify the potential hydrologic impacts of future developments in parts of the Karkheh River basin, Iran, and assess their effects on hydroelectricity generation of existing and projected hydropower plants. Results indicate that upstream development could reduce future annual energy production by 254 GWh. Interbasin water transfer from the nearby Sirvan River basin to the Karkheh River basin was also investigated as a viable option to increase future energy production. Simulation results revealed that an average increase in electricity production can be achieved per of annual environmental flow release out of transferred water from Sirvan to Karkheh River basin. [ABSTRACT FROM AUTHOR]

Hydropower plays an important role in electric power systems. It not only interacts with many non-hydropower generation activities but also competes with other water users (industrial, commercial, residential, and agricultural) for limited water resources. Therefore, the objective of this study is to investigate an optimized water allocation scheme within a water resource and electric power management system through developing an inexact water resource and electric power systems planning model (WPEM). WPEM is based on the interval-parameter programming and mixed-integer programming techniques; thus, it can deal with dynamics of capacity expansion and uncertainties associated with system management. The developed method is then applied to a power system with water shortage issues in the future. The results of scenario analysis indicate that WPEM could help get insights into the tradeoff between system benefit and water utilization as well as that between system benefit and environmental concern. Thus, the modeling solutions could be used by water managers for supporting the effective allocation of water among power production, industrial process, agricultural irrigation, commercial activity, and residential use in case of water shortage. [ABSTRACT FROM AUTHOR]

This works aims to develop and study a new reaction microhydro tubular propeller turbine with five blades as a promising answer to solve the lack of energy in rural and remote areas. The first stage is to validate numerical and experimental tests made for the flow behavior for different values of head, discharge, and rotational impeller speed. Using specific mathematical formulations, a blade model configuration is developed based on the velocity triangles at the impeller inlet and outlet and experimental results based on pressure, discharge, and velocity profiles in different turbine sections. Through characteristic parameters, performance curves are obtained allowing comparisons between experimental and computational fluid dynamics (CFD) results. Also, an evaluation of the hydrodynamic behavior is made for a scaled model application by similarity turbo machines theory. [ABSTRACT FROM AUTHOR]

Irrigation districts in the American West and throughout the world have extensive canal networks that could be utilized to generate a significant amount of hydropower. As the world attempts to become less dependent on carbon-based energy resources, small-scale hydropower (SSH) is an attractive potential resource for new energy development. The Middle Rio Grande Conservancy District (MRGCD) in central New Mexico has an extensive canal network, and hydropower is being considered as a viable form of renewable energy. Currently, the MRGCD has identified and categorized nine potential hydropower sites within its system with the goal of maximizing its contribution to the region's energy needs. This paper addresses key issues related to hydropower in irrigation districts and examines the feasibility of incorporating hydropower generation in the MRGCD canal system. With full year-round implementation of SSH generation at the nine locations investigated, the MRGCD could have a generating capacity of 2.2 MW and produce over during the year. This represents an income from power generation for the MRGCD of $1.032 million at the current power prices. More importantly, implementation of SSH would result in 1,340 homes being powered by clean, renewable energy while concurrently delivering water to irrigators. It is the hope of the authors that the case study presented will aid irrigation districts investigating the incorporation of hydropower in their canal networks. [ABSTRACT FROM AUTHOR]

A hierarchical optimization method is presented for an assessment of the potential maximum energy output of the Three Gorges Project and Gezhouba cascade hydropower stations in China. The optimization incorporates a detailed description of daily load dispatching among different types of hydropower units. The optimization method is divided into three levels to render feasible the computation of the global optimization problem. In levels 1 and 2, a genetic algorithm is applied to optimize discharge and water head distribution between the upstream and downstream reservoirs. Level 1 selects the water levels at the beginning of each month in a year. Level 2 selects the water levels at the beginning of each day in a month. Level 3 solves a linear programming problem for allocation of water among the heterogeneous types of hydropower generation. Hydrological data of the years 2004 and 2005 are used to perform an optimized power generation process within the operating rules. The maximal annual energy production could be approximately 61 and 87 MWh higher than the actual recorded energy production in 2004 and 2005, respectively. [ABSTRACT FROM AUTHOR]

Longwall mining is the only technically proven and well-established mining method used worldwide for extracting coal from deep mines. In this paper, two-dimensional (2D) continuum finite-element models of longwall panels are developed and analyzed to understand the interaction of hydraulic-powered support with surrounding rock strata (i.e., roof, floor, and coal seam). The finite-element models thus developed include the structural components of hydraulic-powered support, the surrounding rock mass, and broken rocks. The study focuses on the evaluation of strata behavior while the coal face is supported by hydraulic-powered supports of different capacities. The results from finite-element models are further analyzed in terms of stress distribution in hydraulic legs, abutment, and roof-to-floor convergence. Statistical relations are developed based on deterministic finite-element results, which provide a good correlation with the field measurements. [ABSTRACT FROM AUTHOR]

Optimal design of tunnels and surge tanks is a major concern in the implementation and operation of large hydropower plants, particularly those in which tunnels are long and water hammer is likely. In this paper, flow simulation and an optimization process have been linked in an iterative manner to develop a general model for the optimal design of hydropower tunnels and surge tanks for the emergency condition of operation (maximum surge pressure). The governing equations for the analysis of transient flow in conduits are solved using a finite difference scheme. Furthermore, a genetic algorithm (GA) optimization technique is utilized to select the optimal diameter for the headrace tunnel, penstocks, and surge tanks. The benefit-cost ratio is considered as the objective function in the optimization analysis. The proposed method was used to design diameters for Marun hydropower tunnels (an in-operation large hydropower dam located in southwest Iran). The results were compared with results from a nonlinear optimization technique. They revealed considerable savings in construction cost, attributable to the application of GA. The calculated pressures across the tunnels with and without surge tank agree with valve closure theory and previous studies. The model is able to optimize diameters for a branching system of tunnels and penstocks with surge tanks. [ABSTRACT FROM AUTHOR]

Archimedes screws have become increasingly popular throughout Europe to drive hydropower plants using residual flow from a stream or river. This heightened usage of such screws during the past few years is attributable to their robustness, simplicity, and fish friendliness. Presently the dimensioning of a hydropower site equipped with an Archimedes screw is dependent mainly on the experience of the design engineer. This is so because there is no appropriate theory for the optimal hydraulic design of screws used at hydropower sites, especially for the water-inflow conditions. In this paper, a new analytical model for the water inflow is derived, and the optimal values of the inflow parameters are determined to achieve a planned inflow to the screw. [ABSTRACT FROM AUTHOR]

The power generated by a hydroelectric plant depends on the penstock head loss, the turbine efficiency, and the generator efficiency among other factors. Initially, the functions related to these variables are provided by the equipment manufacturer; however, over time they change as the plant ages. This paper presents a methodology to adjust an efficiency function for each generating unit based on measured data. It is applied using two optimization methods: the generalized reduced gradient and the evolutionary algorithm. A case study with data from a large Brazilian hydroelectric plant demonstrates how the methodology can be employed and compares the performance of the optimization tools. A comparison metric is used to show that the optimal unit efficiency function significantly improves the performance of simulation models to reproduce observed data and better describe the actual operation of the hydroelectric plant. [ABSTRACT FROM AUTHOR]

Representing peak and off-peak energy prices is often difficult in hydropower modeling because the time scale of price variability (hours or less) is much shorter than that needed for many operations planning models (days to months). This work extends and examines the reliability of an existing approximate method to incorporate hourly energy price information into revenue functions used in hydropower reservoir optimization models with larger time steps (weekly or monthly). The method assumes constant head, an exogenously known frequency distribution for hourly prices during each modeled time period (day, week, or month), and a revenue-maximizing operational strategy that allocates hydropower releases in order of decreasing hourly price. The method is extended to the case with minimum instream flow requirements. The reliability of the method was tested for the cases with and without minimum instream flow requirements. Revenue estimates for a hypothetical hydropower site were compared with the exact optimal revenue from solving the hourly optimization problem within one week, and showed less than 1% error by using a finely discretized price-frequency curve. [ABSTRACT FROM AUTHOR]

Acoustic discharge measurement devices (ADM) based on transit time measurements are widely used to measure water flow rates in channels and closed conduits for hydropower applications. In addition to making velocity and discharge measurements, the ADM simultaneously records the speed of sound and the attenuation of the acoustic pulse through the water-sediment mixture. This information can be used to estimate characteristics of the suspension such as the volume fraction of the sediment. Such information is crucial in hydropower plants because of the negative effects solid particles can have on the equipment. In this work, the Atkinson-Kytömaa model for monodisperse particles is applied to analyze the effect of solid particles and other operating parameters on the sound speed and attenuation in water suspensions. This model has been selected because it is suitable for the interested range of applications. The model has been validated by measurements with different particle material (glass, quartz, calcium carbonate), size, size distribution, shape, and concentration. Moreover, the sensitivity of the model to the particle parameters has been investigated and the critical parameters for monitoring applications have been identified. [ABSTRACT FROM AUTHOR]

In 2005, thermoelectric power accounted for 41% of all freshwater withdrawals and roughly 3% of all consumptive use in the United States. With the demand for electricity projected to increase by 24% by 2035 concerns have been raised as to the availability of water for this growing industry; particularly, as the siting of several new thermoelectric facilities have been challenged on the basis of water supply. To address this concern we estimate the potential impact of water availability on future expansion of the thermoelectric power industry. Specifically, both the extent and location of thermoelectric developments at risk due to limited fresh water supply is estimated for a variety of alternative energy futures that differ according to the assumed mix of fuels utilized in new plant construction. According to the analyzed scenarios water consumption for thermoelectric power generation is projected to increase by 36-43% between 1995 and 2035, with much of this development expected to occur in basins with rapidly growing demands in the nonthermoelectric sectors. To identify where this thermoelectric development might be problematic, projected future thermoelectric production has been mapped onto basins subject to limited water availability. For the purposes of this study, water availability is defined as a local ratio of water demand to physical water supply. Results suggest that 10-19% of all new thermoelectric power production is likely to be sited in watersheds with limited surface and/or groundwater availability. These problematic watersheds are largely located in the West. [ABSTRACT FROM AUTHOR]

In many watersheds around the world where the importance of assessing a watershed as a whole is overlooked, new water resources projects are designed solely based on historic flow data. Such projects might fail to operate satisfactorily when designed without considering the uncertainties associated with future hydrologic changes. In this study, a system dynamics model (SDM) is developed to quantify the potential hydrologic impacts of future developments in parts of the Karkheh River basin, Iran, and assess their effects on hydroelectricity generation of existing and projected hydropower plants. Results indicate that upstream development could reduce future annual energy production by 254 GWh. Interbasin water transfer from the nearby Sirvan River basin to the Karkheh River basin was also investigated as a viable option to increase future energy production. Simulation results revealed that an average increase in electricity production can be achieved per of annual environmental flow release out of transferred water from Sirvan to Karkheh River basin. [ABSTRACT FROM AUTHOR]

The flow regime of rivers is a complex but important measure of environmental quality and one that can be significantly impacted by conventional hydropower generation. While traditional hydropower scheduling creates a periodicity in downstream flows corresponding to seasonal and daily electricity demand patterns, deregulated electricity markets may provide financial incentives to further alter flows, as utilities respond to hourly market dynamics. This study investigates the potential for deregulated markets to impact both a hydropower utility's revenue stream and downstream flow regimes. Six operating scenarios are explored: (1-2) full-market participation (including real-time energy), with and without flow reregulation; (3) day-ahead market only; and (4-6) run-of-river operations (ROR), with and without flood control and flow reregulation. Results suggest that, relative to a day-ahead-only scenario, the scale of any differences in flow regime resulting from full-market participation is relatively small compared to the additional revenue-generating potential of such a strategy. Implementing a run-of-river policy frequently yields "more natural" flow regimes than the day-ahead only scenario; but, in some cases these improvements are modest, and in others the ROR scenarios exacerbate deviation from unregulated flows. Regardless, the effects of implementing an ROR strategy come at a substantial cost in terms of foregone hydropower revenue. [ABSTRACT FROM AUTHOR]

Stochastic dual dynamic programming (SDDP) is one of the few methods available to solve multipurpose-multireservoir operation problems in a stochastic environment. This algorithm requires that the one-stage optimization problem be a convex program so that the efficient Benders decomposition scheme can be implemented to handle the large state-space that characterizes multireservoir operation problems. When working with hydropower systems, one usually assumes that the production of hydroelectricity is dominated by the release term and not by the head (storage) term to circumvent the nonlinearity of the hydropower production function. Although this approximation is satisfactory for high head power stations for which the difference between the maximum and the minimum head is small compared to the maximum head, it may no longer be acceptable when a significant portion of the energy originates from low and/or medium head power plants. Recent developments improve the representation of the nonlinear hydropower function through a convex hull approximation of the true hydropower function. A network of hydropower plants and irrigated areas in the Nile Basin is used to illustrate the difference between the two SDDP formulations on the energy generation and the allocation decisions. [ABSTRACT FROM AUTHOR]

Environmental regulations have required from hydroelectric power plants more effective means of restricting the access of fish into the draft tube of hydraulic turbines. The decline of fish populations on rivers used for electricity generation has motivated the installation of mechanical gates as fish barriers on the tailrace pipe of hydroelectric power plants as a technical solution to preserve aquatic wild life. However, variations in the flow conditions through the turbine runner may modify the performance characteristics of turbines, thus affecting their capacity for electricity production. This note presents an experimental study of the influence of draft tube gates on the hydraulic forces acting on Francis turbines. A Francis turbine test bench was specially designed to allow this investigation. Measurements of the hydraulic thrust in relation to the level of flow restriction at the draft tube exit indicate that the mechanical gates excessively increase the axial load on the runner shaft, which may shorten the hydrogenerator unit life. [ABSTRACT FROM AUTHOR]

An effective numerical method to compute hydraulic resonance in pressurized piping of hydropower systems is presented. For this purpose, the impulse response method is used, i.e., a unit pressure impulse is introduced at the downstream waterway as an exciter. The method of characteristics is used to solve the governing equations for the hydraulic transient and to get the pressure response of the system in the time domain. The discrete Fourier transform is used to compute the frequency response of the system which gives the resonance frequencies in the hydropower plant system. To increase the accuracy of the results, unsteady friction is incorporated into the methodology. The influence of the unsteady friction, wave speed, and power on the pressure response diagram is investigated for the waterway of a multiunit hydropower plant which has been recently installed. Computed results agree very well with those obtained from the standard method of the characteristics. [ABSTRACT FROM AUTHOR]

The impacts of climate change on medium-term reservoir operations for the Peribonka water resource system (Quebec, Canada) were evaluated with annual and seasonal hydropower production indicators and flood control criteria. According to simulations under the current operating rules in a climate change context, the tendency is for a reduction in mean annual hydropower production and an increase in spills, despite an increase in the annual average inflow to the reservoirs. The main results indicate that annual mean hydropower would change by -12 to +2%, and spills by -49 to +152%. A broad range of climate projections—a combination of five general circulation models with two greenhouse gas scenarios each—were used in order to evaluate the uncertainty of these future potential climates on floods and hydroelectric production. Climate projections were downscaled with the change factor method (also called the Delta method) at a horizon centered in 2050. To represent natural variability, a stochastic weather generator was used to produce 30 synthetic climate series of 30 years each, representative of each climate change projection as well as of the climate of the control period. The hydrological impacts of climate change were evaluated with a lumped hydrological model and the hydrological regimes were analyzed according to spring flood characteristics and the average inflows. In general, the projections indicate an increase in annual inflow, earlier peaks and greater volumes during the spring flood. The analyses show that a power plant managed with a reservoir is sensitive to the operating rules and that these rules should be re-examined in order to take account of new seasonal hydrological contexts. [ABSTRACT FROM AUTHOR]