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The sustainable use of water reservoirs is threatened by sediment accumulation, but loss of storage volume can be prevented or limited by appropriate sediment management strategies that work in a variety of expected conditions. The development of a reservoir flushing strategy, tested against water and sediment inflow that might occur over centuries, is presented. A typical length of water and sediment records of 50 years was used to represent the range of variability within a year, and extended by deducing longer term inter-annual variability from suitable indicators (sediment cores in natural lakes, tree-ring chronologies etc.). It was concluded that, over past centuries, water inflows over a period of 50 years could typically vary by about 10%, while sediment inflows could vary by about 20%. The resilience of flushing rules derived solely on the recorded dataset over centuries-long periods was tested using a long-term computer simulation of reservoir sedimentation. The simulations showed that some modifications to the flushing rules would increase performance over centuries-long periods. Although the approach was derived for a specific project, it is based on some generally applicable parameters, such as the discharge at which operation stops and the moving average of the annual peak flow. [ABSTRACT FROM AUTHOR]

The head–discharge relationship of an overflow weir is a prerequisite for flow measurement. Conventionally, it is determined by regression methods. With machine learning techniques, data-driven modelling becomes an alternative. However, a standalone model may be inadequate to generate satisfactory results, particularly for a complex system. With the intention of improving the performance of standard gene expression programming (GEP), a hybrid evolutionary scheme is proposed, which is coupled with grey system theory and probabilistic technique. As a gene filter, grey relational analysis (GRA) eliminates noise and simulated annealing (SA) reduces overfitting by optimising the gene weights. The proposed GEP-based model was developed and validated using experimental data of a submerged pivot weir. Compared with standalone GEP, the GRA–GEP–SA model was found to generate more accurate results. Its coefficients of determination and correlation were improved by 3.6% and 1.7%, respectively. The root mean square error was lowered by 24.8%, which is significant. The number of datasets with an error of less than 10% and 20% was increased by 15% and 12%, respectively. The proposed approach outperforms classic genetic programming and shows a comparative error level with the empirical formula. The hybrid procedure also provides a reference for applications in other hydraulic issues. [ABSTRACT FROM AUTHOR]

This study contributes to emerging computationally efficient methods to account for multi-purpose reservoir operations at the dam design stage. In many cases, the water supply reliability objective introduces binary variables into an otherwise simpler linear programming (LP) formulation. This has led to widespread use of evolutionary methods such as particle swarm optimisation (PSO). Combining the branch and bound (BB) method with a hybrid PSO–LP, this study presents a new BB–PSO–LP algorithm to solve the joint design and operations problem. The proposed BB–PSO–LP algorithm was benchmarked against classical versions of the BB algorithm and PSO–LP. Superiority of the BB–PSO–LP algorithm was demonstrated by finding slightly better solutions in a shorter time. That said, PSO–LP also led to acceptable results in a similar time. Although the BB algorithm was found to be efficient in problem solving, under certain conditions it is difficult for the BB method to find a feasible solution. [ABSTRACT FROM AUTHOR]

This study achieved three goals to clarify the impact of a vegetation patch on flow adjustment and velocity. First, a valid equation for the interior adjustment distance (Ld) inside a model patch was developed for a wide range of velocities and flow depths. Second, the minimum distance inside a patch beyond which the resuspension of fine sediment is suppressed (Lmin) was found to be related to the position at which the local velocity decreases to the threshold for generating stem-scale turbulence. Lmin primarily depends on the flow blockage (Cdab) and the stem diameter (d): a shorter Lmin is a result of a larger Cdab and a smaller d. An equation was formulated for estimating Lmin. Third, for the fully developed flow region inside a patch (L > x > Ld), an equation was developed to estimate the increase in the mean velocity in the bare channel relative to the overall mean channel velocity. For Cdab < 2, this fraction is controlled by both the patch density (ad) and the patch blockage (b/B) whereas, for Cdab > 2, this fraction is controlled by only b/B. A suggestion for choosing the patch size in future flow and sediment research projects is presented. [ABSTRACT FROM AUTHOR]

Since the major flood event in 2007, RPS has been deeply involved in investigating, understanding and reducing flood risk across the Hull and Haltemprice catchment. RPS has developed and refined a complex integrated catchment model by combining Yorkshire Water's model of below-ground assets with data for the watercourses and overland flow paths obtained from the Environment Agency, East Riding of Yorkshire Council and Hull City Council. RPS used the model to identify major schemes, leading to the design of flood alleviation schemes at Willerby and Derringham, Anlaby and East Ella, and Cottingham and Orchard Park. With further enhancements, the model has been used to better understanding of the complex interactions between the various water systems and solutions are being identified for a long-term plan. Hull has many unique features, driven by its topography, geology and the historical developments of its sewerage network and waterways. These specific challenges require bespoke solutions and there is a clear desire among the partner organisations to work together to drive contemporary blue–green solutions. This requires multi-agency working and progressive thinking to deliver effective flood risk management. This paper reviews the challenges in understanding and resolving these issues. [ABSTRACT FROM AUTHOR]

This paper presents the application of hydraulic modelling for the prediction of pipe bursts in a water distribution system (WDS). As a case study, more than 1430 km of pipelines within 29 water pressure zones (PZs) in Bendigo and Castlemaine WDSs, located in Victoria, Australia, were modelled and calibrated using an InfoWorks WS hydraulic model. A pressure index (PI) was defined to quantify the intensity of high pressures in the WDS pipes. The PIs for all the PZs were calculated using hydraulic model simulations. Ten years of actual pipe burst data (2007–2017) in the studied WDSs were used in the research. A burst index (BI) was used to measure the burst rate for the length of pipe network within the study area. A mathematical relationship between PI and BI was proposed based on the first eight years (2007–2015) of burst data and the results of the hydraulic modelling in the same period. The number of pipe bursts for the last two years (2016–2017) in each PZ was then predicted according to the proposed mathematical relationship. The predicted number of bursts fitted well with the actual recorded pipe burst data, with a coefficient of determination of 0.98. [ABSTRACT FROM AUTHOR]

Concrete face rockfill dams are widely used in hydropower engineering because of their many advantages. As important structures, if the performance of the concrete face slab and the impervious curtain is weakened, leakages and even serious dam failures can occur. Based on an equivalent quasi-continuum medium model, three-dimensional finite-element numerical simulations of the seepage behaviour of Miaojiaba dam, China, are performed. The seepage field and seepage characteristics, including the phreatic line, maximum hydraulic gradient and seepage discharge, are analysed quantitatively and systematically under various abnormal conditions. The results show that cracks in different areas of the face slab and different degrees of degradation in the impervious curtain influence the seepage field in different ways, with cracks in the lower face slab being the most serious. Ensuring that the face slab and impervious curtain are working as intended is very important for the integrity of the dam. Therefore, the design and construction quality of impervious structures should be strictly controlled. Under abnormal conditions, seepage control should be realised to ensure the safety and stability of concrete face rockfill dams. [ABSTRACT FROM AUTHOR]

A large number of multi-reservoir hydropower systems are in operation all over the world in order to meet increasing power demand. To date, different optimisation methods have been applied to multi-reservoir systems. However, overcoming the computational effort required to find an optimal operating policy for multi-reservoir systems still remains a difficult task. The aim of this study was to optimise the operation of complex multi-reservoir hydropower systems using profust reliability – a theory used in the reliability analysis of manufactured systems. The profust-reliability-based optimisation model was applied to a system with reservoirs connected in series and parallel to determine monthly operating policies for synthetically generated streamflow. The results show that the model is applicable to multi-reservoir systems. [ABSTRACT FROM AUTHOR]

A new approach for finding a cost-effective combination of groynes in a channel bend for the prevention of bend scour is presented. A linked simulation–optimisation model is proposed for this purpose. The morphological flow simulation model was developed by solving the shallow-water equations and the Exner sediment continuity equation in a boundary-fitted coordinate system. The optimisation model was developed utilising a binary-coded genetic algorithm. The proposed model can automatically provide a cost-effective groyne series in terms of their number, length and position in any vulnerable channel bend. A constraint in terms of bend scour is also incorporated in the optimisation model, which allows the optimisation model to obtain the best groyne combination for no bend scour. To appraise the performance of the model, it was applied to a hypothetical vulnerable channel bend. The model produced the minimised cost of installation of the groyne system at that location, at the same time as making the location free from bend scour. [ABSTRACT FROM AUTHOR]

Estimation of streamwise depth-averaged velocity and boundary shear stress are important requisites for modelling of river flows associated with flood events. Recently, many methods have emerged to predict these flow variables with great accuracy, but they provide unsatisfactory results in shear layer regions. This paper presents an improved methodology to predict depth-averaged velocity and bed shear stress for a straight compound channel flow. An analytical solution to the depth-integrated turbulent form of the Navier–Stokes equation is obtained. The transverse shear stress in the mixing region is modelled using an effective eddy viscosity concept that contains horizontal coherent structures and three-dimensional bottom turbulence. The secondary flow term is modelled by considering the log-law profile for streamwise velocity and half cosine curve for the transverse velocity component. The analytical solution is successfully applied to a wide range of experimental compound channels and field cases. The efficacy of the present solution has been successfully tested by comparing with observed values. [ABSTRACT FROM AUTHOR]

This paper demonstrates the influence of differential roughness on the boundary shear distribution for compound open channels. A mathematical relationship is derived between the percentage shear force carried by floodplains and five non-dimensional parameters (width ratio, relative flow depth, relative roughness, Reynolds number and Froude number). A procedure for assessing the flow distribution in terms of zonal boundary shear distribution and momentum transfer coefficients at the junction of a compound channel is presented. The efficiency of the model was tested by comparisons with published datasets and large experimental flood channel facility datasets. Compared with other standard approaches, the proposed method provided the least error in the predictions of both boundary shear and flow. The approach was also verified using actual river data and was found to provide good predictions in real-world applications. [ABSTRACT FROM AUTHOR]

For many remote and under-privileged communities, water filtration is the first step of treatments before boiling and/or other higher level treatments. Clogging is a common unavoidable hindrance to such systems, which causes reduced efficiency with regard to the flow rate of filtered water. Backwashing is commonly used to recover the filtration capacity of clogged filter media. This paper presents an improvement of a previously developed simple clogging and backwashing efficiency model for the third-generation IHE family filter, which was developed by Unesco-IHE Institute for Water Education. The earlier simple model considered a linear decay of flow rate due to clogging in a weekly timestep. With the aim of enhancing the model's accuracy, this work considered three other models (a linear model with a daily timestep, a power function model and an exponential model). The performance of the models was assessed using the root mean squared error and chi-squared (χ2) values derived from predicted and measured flow rates through the device during successive clogging and backwashing periods for up to 4 months. The improvements using the linear 1 day model over the linear 7 day model were insignificant. Among the tested models, the power function model provided the best predictions, with an average χ2 improvement of 33% over the previously developed linear model. [ABSTRACT FROM AUTHOR]

Combined weir–gate structures are important structures for controlling the water level, measuring discharge and avoiding sediment deposition behind a weir. They can be used, for example, in irrigation channels and waste water systems. Using three-dimensional numerical software (Flow-3D) and experimental data from the literature, four combined systems of a triangular weir and a rectangular gate with different geometries were simulated. Dimensional analyses were then performed to determine the dimensionless parameters that affect the discharge coefficient of such structures. Four different intelligent system models were used to estimate the discharge coefficient and their results were compared. It was found that Flow-3D is highly capable of simulating the flow over a combined structure. Goodness of fit criteria also showed that the numerical solver estimated the water head and discharge coefficient very well. The results of all the models showed that the discharge coefficient had an inverse relation with the dimensionless parameters h/b, h/d and h/y (h being the water head over the weir, b the gate width, d the gate height and y the distance between the bottom of the weir and above the gate); the discharge coefficients were 0·3–0·9. Accuracy analyses of six intelligent system models showed that the multi-layer perceptron model was the superior model, followed by the M5P model, the regression equation, the radial basis function and the generalised regression neural network model. [ABSTRACT FROM AUTHOR]

The ability of green roof systems to impact stormwater runoff from buildings has been covered in many research studies. However, a lot of these studies looked at long-term retention, with much less work focused on how to model a green roof's response to larger design storms. Work that has examined flow routing for individual rainfall events has focused on empirical routing models that are tuned to the specific roof being modelled. This paper presents a new physics-based model for flow routing based on the green roof module geometry and soil properties, which requires only a single discharge coefficient to be measured. The results of this model were compared with the results of a series of experiments to quantify a modular green roof system's hydraulic response to drawdown and steady rainfall. [ABSTRACT FROM AUTHOR]

A sediment transport predictor based on a review and update of the theory of Ackers and White is proposed. While the core of the Ackers and White theory was retained, the approach to predicting transport rates was updated by introducing some new ideas and modified where opportunities for improvement were identified. A large dataset compiled from the existing literature was used for model calibration and validation. The results showed a good improvement compared with the original Ackers and White equation and some other total load predictors. Better matching with observed data was achieved especially at higher slopes (above 1%) and low submergence ratios (below 50) as well as at the extremes of the sediment size scale, where the applicability was extended to the coarse silt region. Predictions for gravel and coarser sediment were also improved. [ABSTRACT FROM AUTHOR]

A new round of reform of China's electricity market was launched in 2015 to encourage competition among power generation companies. For cascade hydropower stations under multi-partite ownership, an alliance has become a way to improve competitiveness, but the stability of such alliances is affected by multiple factors. Because of the fierce competition caused by incomplete marketisation and oversupply, some hydropower stations show bounded rationality. In this work, the replicator dynamic mechanism was used to analyse the alliance stability of cascade hydropower stations: this provided a two-dimensional (2D) continuous dynamic system and the specific steps for its solution. After detailed analysis of the existence and stability of the equilibrium solution in the 2D continuous dynamic system and the Jacobian matrix, the parameters for convergence process analysis were assessed. The numerical simulation showed that the alliance is positively related to the common additional income and the penalty factor, and has a negative correlation with a single party's initial investment. It was also found that there is an optimal proportion of common additional income distribution, which makes the alliance most likely to succeed. [ABSTRACT FROM AUTHOR]

After continuous use of any filtration device, clogging of the filter media becomes apparent, which eventually causes poor performance of the filtration process. Back-washing is a common technique that is used for the recovery of the filtration capacity of clogged filter media. This paper presents the development of a simple clogging and back-washing efficiency model for a special filter medium. The 'third-generation IHE family filter' was developed by the Unesco-IHE Institute for Water Education and is widely used for treating arsenic-contaminated water in many countries, including Bangladesh. Several field tests were conducted at three different sites in Bangladesh having different qualities of influent water. The model coefficients developed were derived using the collected data on flow measurements through the device during successive clogging and back-washing periods of up to 4 months. The developed model with the selected model coefficients can simulate field measurements on flow retardation and recovery with good accuracy. Eventually, selected model coefficients (clogging factors) for the three sites were correlated with the respective ammonium and iron contents in the influent water. It was found that the clogging factor linearly varies with the ammonium and iron contents of the inflow water. [ABSTRACT FROM AUTHOR]

The accuracy of five soft computing techniques was assessed for the prediction of monthly streamflow of the Gilgit river basin by a cross-validation method. The five techniques assessed were the feed-forward neural network (FFNN), the radial basis neural network (RBNN), the generalised regression neural network (GRNN), the adaptive neuro fuzzy inference system with grid partition (Anfis-GP) and the adaptive neuro fuzzy inference system with subtractive clustering (Anfis-SC). The interaction between temperature and streamflow was considered in the study. Two statistical indexes, mean square error (MSE) and coefficient of determination (R2), were used to evaluate the performances of the models. In all applications, RBNN and Anfis-SC were found to give more accurate results than the FFNN, GRNN and Anfis-GP models. The effect of periodicity was also examined by adding a periodicity component into the applied models and the results were compared with a statistical model (seasonal autoregressive integrated moving average (Sarima)) to check the prediction accuracy. The results of this comparison showed that periodicity inputs improved the prediction accuracy of the applied models and, in all cases, the soft computing models performed much better than the Sarima model. The periodic RBNN and Anfis-SC models increased the MSE accuracy of Sarima by 25·5–24·7%. [ABSTRACT FROM AUTHOR]

This paper introduces a 'collocated discrete subdomain meshless method' to solve shallow water equations for free-surface flows with conservation of sediment mass. The computational domain in the method is discretised by distributed nodal points. Shape functions are made using the moving least-squares method for efficiency and simplicity. A number of collocation points, independent of nodal points, are used to form the specified residual function. The sum of residuals at the collocation points for each subdomain is zero in the problem domain and boundaries. In addition, boundary conditions are readily enforced. The model was verified by comparing results of simulated and physically modelled dam-break flows. There was good agreement between the analytical solution and experimental measured data, and a high convergence rate and efficiency were achieved. The method appears to have significant potential for investigating a variety of problems concerning coupled flow with sediment transport. [ABSTRACT FROM AUTHOR]

Based on data envelopment analysis, water efficiency and productivity were measured with the aim of reducing water use in metropolises. Alternative measures of efficiency were evaluated and the productivity was decomposed into several components. The correlation between regional economic indices and water quantities was also analysed. For the case of water use in metropolitan Tehran, an average efficiency of 94% was measured and progress in total productivity was calculated to be 14%. The efficiency scores of other metropolises in Iran were calculated to be about 30–50% less than that of Tehran. Reasonable estimates for the threshold of water use in Tehran were obtained. This paper also presents the issues of the plans for improving water efficiency and productivity and increasing water availability for users. This work identified the significant effects of regional economic indices on water efficiency and productivity calculations in metropolises of Iran. [ABSTRACT FROM AUTHOR]

Stepped spillways are commonly used in hydropower engineering, landscape irrigation and aeration tanks due to their high energy dissipation and superior aeration. This study used the k–ε turbulence model to study the pressure distributions of three types of stepped spillways with different horizontal face angles in fully developed skimming-flow regions. The horizontal surfaces of V-shaped steps exhibited a pressure peak that decreased from both sidewalls to the axial plane, while those of inverted V-shaped steps exhibited the opposite pattern. There was barely any variation from those of traditional stepped spillways. Negative pressures on the vertical surfaces of V-shaped, inverted V-shaped and traditional stepped spillways occurred near the sidewalls, near the axial plane and along the entire cross-section, respectively. For all the stepped spillways studied, the minimum pressure decreased with increasing Froude number and increasing absolute values of the horizontal face angles. [ABSTRACT FROM AUTHOR]

In the present research, the application of a proposed, modified, central force optimisation method for multi-objective optimisation of water distribution systems is examined. This new method is based on a central force optimisation algorithm in which the non-dominated sorting plus crowding distance calculator mechanisms produce optimal Pareto solutions in objective functions trade-offs. Minimising pipe-sizing cost and maximising new reliability measures are considered as objective functions. The method is written in Matlab and linked with Epanet water distribution software. Employing the method to solve the Kadu and Khorramshahr water distribution networks shows its capability to produce well-distributed optimal Pareto solutions for cost and reliability. Also, by utilising a fuzzy ranking method, a best compromise solution for two objectives can be extracted from the optimal Pareto set. [ABSTRACT FROM AUTHOR]

The present study focuses on out-of-plane and in-plane vibrations of sluice gates due to the fluid-structure interaction based on numerical modelling, using the finite-element method. Primarily, the vibration of the gate was restricted to a single direction, detaching the horizontal and vertical vibrations of the gate so as to exclude their interaction. Results indicated that, if the edge of the gate is bevelled at an angle of 45°, the lowest amplitudes of horizontal vibrations are obtained. Whereas the maximum horizontal vibrations are associated with the uppermost values of the reduced velocities, for example vr > 3·5, as well as the gate's normalised opening height δ/ d of about 0·8, the maximum vertical vibrations are attained for intermediate values of vr, at about 3, and δ/ d = 0·8. If both the horizontal and vertical vibrations are mutually considered, the two-dimensional reduced velocities vr x and vr y and the structural natural frequencies fx and fy become relatively different compared to these of single-way vibrations. Results also indicated that the amplitudes of the horizontal vibrations in the authors' previous analyses were considerably greater than those of single-way horizontal vibrations. The maximum amplitude of the horizontal vibrations was observed to be close to the out-of-plane natural frequency, when 3·5 < vr x < 7 and vr y > 10. For vibration frequencies close to the vertical natural frequency fy, however, the dominant vertical vibrations occur for 2 < vr y < 4. [ABSTRACT FROM AUTHOR]

Experimental data characterising dispersion within Typha latifolia were previously collected in a laboratory setting. This mixing characterisation was combined with previously proposed computational fluid dynamics modelling approaches to predict residence time distributions for vegetated stormwater treatment pond layouts (including a wetland) derived from Highways England design guidance. The results showed that the presence of vegetation resulted in residence times closer to plug flow, indicating significant improvements in stormwater treatment capability. The new modelling approach reflects changes in residence time due to mixing within the vegetation, but it also suggests that it is more important to include vegetation within the model in the correct location than it is to accurately characterise it. Estimates of hydraulic efficiency suggest that fully vegetated stormwater ponds such as wetlands should function well as a treatment device, but more typical ponds with clear water need to be designed to be between 50% and 100% larger than their nominal residence times would suggest when designed against treatment criteria. [ABSTRACT FROM AUTHOR]

A one-dimensional numerical model was developed to simulate the hydrodynamic processes in a large and complex river network located in the middle and lower Yangtze River basin, China. The main stem of the river is connected to two large lakes, Dongting and Poyang, through many branches. A mass conservation method was used to determine the lateral inflows from local basins along the river. The model was verified against measured data at a large number of hydrological stations over a 2-year period. The water levels and discharges predicted by the model were found to generally agree well with the measured data. The model was then used to reproduce the flow process during a large flood event that occurred in 1998. It was found that the two large lakes could store a large volume of water and thus played an important role in attenuating the flood impact. [ABSTRACT FROM AUTHOR]

Effective reservoir operation is achieved using suitable rule curves to control the release of water following the release criteria. Conditional cuckoo search (CCS) algorithms and conditional particle swarm optimisation (CPSO) were linked with a reservoir simulation model to identify adaptive optimal reservoir rule curves. Three cases (normal, dry and wet years) were considered when producing the rule curves depending on the inflow pattern and inflow period. Lampao reservoir in Thailand was used to illustrate application of the method. The results showed that the new rule curve patterns produced by CCS algorithms and CPSO in a normal year were similar to the patterns obtained by conditional ant colony optimisation and current usage patterns. However, the obtained rule curves for wet and dry years were quite different from those for the normal year. Average water shortages using the normal-year inflow were less than using the dry-year inflow by 24·05% and 18·92% for CCS and CPSO models, respectively. Situations of water shortage when using the normal-year rule curves can best mitigate the water situation. In conclusion, the adaptive rule curves were suitable for reservoir operation under all inflow cases. [ABSTRACT FROM AUTHOR]

A methodology for determining reservoir operating rules in a multi-reservoir water system using a linear programming model is presented. The methodology includes optimisation and simulation tools within an implicit stochastic optimisation framework. It aims to support water decisions in a participatory and integrated risk management approach to drought events by selecting and evaluating reservoir operating rules based on hydrological scenarios. A test case widely used in the literature is investigated to evaluate the performance of the proposed methodology. Plausible results are obtained, encouraging the possibility of applying linear programming in identifying reservoir rules, particularly under drought conditions. [ABSTRACT FROM AUTHOR]

This paper assesses the suitability of two simple parameterisation-simulation-optimisation (PSO) models used to set up release policies for water supply reservoirs. Operations guided by the generated rules are compared against those defined via classic stochastic dynamic programming (SDP). One PSO model, PSO-SOP, is a variant of the reservoir standard operating policy (SOP) and the other, PSO-ZON, is based on reservoir zoning. Both models were applied to the operation of a reservoir in northeastern Brazil under several synthetic 100-year monthly inflow scenarios. Operations were also carried out by the original SOP and by deterministic optimisation based on perfect inflow forecast, the latter used as a benchmark. In the majority of the 100 scenarios utilised, the performance of both SPD and PSO-SOP was found to be superior to that of PSO-ZON and SOP. Furthermore, the uncomplicated PSO-SOP model performed even better than the more complex SDP. [ABSTRACT FROM AUTHOR]

As a cantilever failure involves rapid channel widening and delivers a large volume of sediment into the channel, it is important to understand this mechanism from the river engineering point of view. Different types of riverbank failures have been investigated in several previous studies, but these works have limitations in understanding the complex mechanisms of cantilever failure regarding the coupling of fluvial erosion with that failure. Experiments were thus carried out to assess the underlying mechanisms of cantilever failure using three types of cohesive materials classified on the basis of their percentages of silt-clay content. The experiments showed that fluvial erosion of the lower part of cohesive riverbanks progressively undermines the upper part during the initial stage of a cantilever failure. Tension cracks then develop at the upper surface of the cohesive riverbanks and beam failure occurs thereafter. A mathematical model of cantilever failure was also developed. The model uses a triple-grid approach to simulate the behaviour of a cantilever within the framework of fluvial erosion and the cantilever's subsequent failure. The simulated results show good agreement with the experimental results in terms of spatial-averaged bank width and water level along cohesive riverbanks. [ABSTRACT FROM AUTHOR]

It is difficult to find an algorithm to distribute specific reservoir releases to the floodgates of a hydropower plant in the flood season. In this study, based on a classification of floodgate combinations and the outflow from a hydropower plant, a floodgate table has been established. In order to provide a reasonable scheme for the distribution of releases to the floodgates, this paper summarises the principle of the distribution. A multi-step progressive optimality algorithm (MSPOA) is adopted for optimal floodgate operation in cascade reservoirs and applied to calculate the outflow from each reservoir of cascade reservoirs. Subsequently, according to the summarised principle, the method of bisection is used to search floodgate combinations from the floodgate table for the distribution of releases to the floodgates. To verify its feasibility, the proposed method is applied to optimal floodgate operation in a cascade reservoir system that has four hydropower plants on the Yalong River. A comparison of the application results of the progressive optimality algorithm and MSPOA methods shows that the proposed method can provide reasonable results for flood control and can distribute specific reservoir releases to the floodgates for each reservoir in the cascade reservoir system accurately. [ABSTRACT FROM AUTHOR]

A finite-difference method based on a shallow water equation (SWE) is developed in this study for simulation of dam-break flows. A second-order leap-frog scheme constructed in a staggered grid system is used to discretise the original SWE. To minimise the spurious fluctuations of the free surface near the moving front, an artificial diffusion term, which is simple, effective and easy to implement in the staggered-grid leap-frog system, is introduced on the right-hand side of the continuity equation. The model is verified against a wide range of classical analytical solutions, experimental data and other previous numerical results. The model is also validated against the real case of the Malpasset dam-break event. It is demonstrated that the improved model is well balanced and robust, and can accurately capture the movement of the dam-break flows. [ABSTRACT FROM AUTHOR]

Shallow flows can play a significant role in sediment management for dam reservoirs (e.g. sedimentation in shallow reservoirs and free-flow flushing operation). When shallow flow emerges with symmetric or asymmetric patterns, the flow domain exhibits complex three-dimensional (3D) features (e.g. helical flows). This study focuses on the numerical modelling of the velocity field in shallow reservoirs with varying geometries and also varying bed conditions (i.e. flat and misshaped beds). A fully 3D numerical model using the finite-volume method was utilised to reproduce the 3D flow velocity field. The experimentally measured surface velocity in all cases and velocity profiles in one case were used to validate the model. The numerical results showed that a slight disturbance in the inflow boundary condition results in a steady asymmetric flow pattern in reservoirs with a higher defined shape factor, but does not affect the flow pattern in reservoirs with a lower defined shape factor. Nonetheless, the simulated and measured flow velocity fields are reasonably consistent in all cases. These results can be used to optimise the design of sand traps or water storage facilities, and also to optimise sediment management in existing reservoirs. [ABSTRACT FROM AUTHOR]

Pier scour has caused bridge failures with catastrophic consequences. The aim of this study was to develop and verify a mathematical model for pier scour predictions. A new approach is taken that combines shallow-water equations with non-hydrostatic pressure corrections and a non-uniform mesh in the horizontal with terrain-following layers in the vertical. This approach significantly improves computational efficiency from the conventional computational fluid dynamics approach. It is concluded that, emerging from the lateral sides of a pier (cylinder), scour deepens while the patterns migrate upstream towards the pier's upstream nose. On the upstream side, scour continues to grow until the bed slope reaches the angle of repose of sediments. On the downstream side, scour grows until equilibrium is reached. The scour hole is shallower downstream than upstream of the pier. The presence of the pier causes a strong downflow near its upstream nose, a strong vortex at its foot on the upstream side and a weak vortex on the downstream side. The predicted flow velocity and scour depth agree well with measurements. The terrain-following layer feature is particularly useful for scour computations; the high efficiency makes the model practical for field-scale applications, which are highly relevant to improved design of pier foundations and pier scour control. [ABSTRACT FROM AUTHOR]

A model has been created for calculating the balanced diversion ratios of flow rate and sediment in the branches of a bifurcated river. The model is based on the extremity law of energy dissipation rate, and involves solving the simultaneous equations of flow and sediment motion for uniform flow in an open channel. The model has been verified by measured data obtained from the Meizizhou and Baguazhou branches of the Yangtze River in China. The parameters that influence the diversion ratios, such as river width, channel roughness and the total inflow, have been analysed. It was found that balanced diversion ratios are more sensitive to river width and roughness than to total inflow. Measures to regulate the Baguazhou branch have been compared further and analysed. The conclusions of this study can provide a theoretical basis for future regulation of the Baguazhou river branch. [ABSTRACT FROM AUTHOR]

More complex operation requirements and multi-objective control needs are the main characteristics of large-scale cascaded hydropower system operations in China. In this study, a hybrid method is developed for addressing multi-objective optimisation of such operations. This method integrates an evaluation technique, an integrated search method and an improved quadratic programming method. The evaluation technique is first presented to combine multiple objectives through introducing a set of evaluation coefficients of the generated energy. The integrated search method, which is based on a progressive optimal algorithm, discrete differential dynamic programming and a group strategy, is proposed to explore initial feasible solutions and to determine the rational search range. Finally, the improved quadratic programming method is developed to dynamically handle complex system generation limitation constraints. This method iteratively solves the reformulated problem to attain a better solution. The proposed method was applied to Hongshuihe River hydropower system. This method effectively coordinates two competing operational objectives and significantly enhances the total power generation during the dry season, compared with the existing model and methods. [ABSTRACT FROM AUTHOR]

Utilisation of submerged vanes in front of intake ports is an effective approach to address sedimentation in lateral intakes from rivers. Strategically installed, these flow-training structures could increase the mid-depth and near surface flows into the intake, and simultaneously prevent bed-load transport from entering the intake channels. The effectiveness of submerged vanes depends on their number, shape, dimensions and configuration. Determination of optimum values for dimensions or configuration of the vanes is very challenging as the effect of many parameters, which are effective in sedimentation in the intake zone, must be investigated. In this study, effort has been made to determine appropriate dimensions of submerged vanes that are installed in front of a 90° intake from a straight channel. Fuzzy TOPSIS, a multi-objective optimisation method, has been utilised for the optimisation process by considering ten parameters. The simulations have been conducted for three discharge ratios of 0·11, 0·16 and 0·21. The results show that a height of 0·2 times the flow depth, and a length of four times the vane height are the appropriate dimensions for utilisation of submerged vanes in front of the lateral intakes from straight channels. [ABSTRACT FROM AUTHOR]

A preliminary flood risk assessment estimated that 20 100 households in Liverpool are at risk of surface water flooding in a once in 200 year event. This paper describes a detailed investigation to reassess the numbers and locations of properties at risk, and then to determine the possible solutions and associated costs. The investigation involved integrated working between Liverpool City Council, the Environment Agency, United Utilities and CH2M. The project included data collection; integrated hydraulic modelling of the sewer network and watercourses (including overland flow modelling) using InfoWorks 2D; analysis; high-level option development; and cost-benefit analysis of the potential solutions. Solutions considered included surface water management, culvert rehabilitation and optimisation of the sewerage and watercourse infrastructure. The technical aspects discussed in this paper include creating the integrated model, flood mapping, 'hot spot' identification and modelling of possible flood alleviation options. The project will enable creation of a multi-agency investment and action plan to reduce the risk of flooding in high-risk locations. The paper also reviews the advantages and disadvantages of the project for all the parties and discusses what lessons can be learnt for future integration and partnership. [ABSTRACT FROM AUTHOR]

Laboratory experiments were conducted in a large-scale meandering compound channel to investigate the flow patterns at the apex and cross-over sections. An equation in curvilinear co-ordinates was derived from the momentum equation and the flow continuity equation. In this equation, two shear stress terms are ignored due to their negligible contributions such that simple expressions are obtained. Several groups of experimental data from the published literature were used to verify this model. Comparison of the experimental and predictive results indicates that the proposed method is capable of accurately forecasting the stage discharge in meandering compound channels. Finally, the simple analytical solution of this model and the velocity parameter are further discussed. [ABSTRACT FROM AUTHOR]

The paper details an integrated physical experimental and numerical model study undertaken to investigate the channel evolution processes. The experiments were conducted in a laboratory flume, in which channel evolution and bed level changes were observed. The numerical model was based on a joint two-dimensional hydrodynamic and sediment transport model. The numerical model prediction agreed generally well with the results of physical experiments and these two approaches were used jointly to investigate the dynamic channel shift process. A series of characteristic phenomena were reproduced including: the shallowing and widening of the initial channel, the formation and development of a regular sequence of alternate bars and pools, erosional bumps of the bank line and the evolution from a regular channel to an irregular channel with the occurrence of an abrupt shift of the main flow. [ABSTRACT FROM AUTHOR]

Existing Muskingum hydrological routing models adopt a single criterion in the calibration process. Some models minimise the sum of the squared deviations between estimated and observed outflows (outflow criterion), while others minimise the sum of the squared deviations between the estimated and observed storages (storage criterion). However, models that adopt the outflow (storage) criterion result in a poor fit to the observed storages (outflows). This paper presents a new approach that incorporates both criteria in the calibration process and aids trade-off analysis. The multi-criteria function is expressed as a weighted function of normalised outflow and storage criteria, representing the deviations from ideal outflow and storage values. The routing procedure is based on the author's four-parameter Muskingum model with constant parameters and the fourth-order Runge-Kutta method. The proposed model was applied to three examples. A criterion weight of 0·4-0·6 was found to produce an excellent trade-off between outflow and storage criteria. The results show that the model substantially improves on both criteria compared with single-criterion models. The proposed model, which properly captures the entire flood propagating characteristics in calibration, should be of interest to hydrological engineers and practitioners. [ABSTRACT FROM AUTHOR]

This paper considers the erodible river corridor, which is the area in which the main river channel is free to migrate over a period of time. Due to growing anthropogenic pressure, predicting the corridor width has become increasingly important for the planning of development along rivers. Several approaches can be used to predict the future erodible corridor width but the results possess a large degree of uncertainty in all cases. The work presented here addresses prediction of the erodible corridor width of a reach of the River Irwell, UK, taking into account the uncertainty that arises from input parameters such as representative discharge, channel width, sediment and so on. The work adopts a probabilistic framework for assessment using Monte Carlo type simulations. Future river corridor width predictions, based on a model calibrated on past observations, are presented in a probabilistic manner using confidence levels. The results indicate the necessity of capturing input variability in the modelling process. Furthermore, the understanding gained from a relatively simple model used in a probabilistic framework is greater than a more complex one where only a few runs are feasible. [ABSTRACT FROM AUTHOR]

The left branch of the Bagua reach of the Yangtze River in China is vital for the regional economy and shipping. This paper describes a numerical modelling study, based on an extensively verified shallow-water solver, to simulate the effects of a diversion dyke on the flow around Bagua Island. A boundary-fitted curvilinear mesh of high resolution was generated, covering the model domain which stretched from Sihao Wharf to Gangchi. The simulation was calibrated against the field observations and physical model tests for the dry season at some velocity measurement cross-sections and water level gauging stations. The results showed that a diversion dyke can modify the water levels, flow fields and the flow rates to the left branch of the river. The water levels on the left side of the upstream channel and in the left branch were mainly affected. The left branch's diversion ratio also varied greatly when the length and the angle of the diversion dyke changed. However, when the angle of the diversion dyke was about 70°, the diversion ratio barely changed with the length of the dyke. The results are useful for channel management and regulation. [ABSTRACT FROM AUTHOR]

In the UK, a disparity exists between modelled future weather/climatic patterns and the assessment of climate change impact on flood risk in the UK statutory planning process. Specifically, the impacts of climate change on the physical characteristics of a river catchment (e.g. land-use change, vegetation cover, soil moisture) are not considered when generating climate change weighted design flood events to assess the potential impact of flooding on a development in the future. Instead, a UK-wide averaged perturbation factor is applied. In this paper, a method is tested to integrate climate change data from UK climate projections 2009 (UKCP09) into design flood estimation methods (ReFH) as part of the current planning process. Scenarios are developed for a single, critical duration, 1% probability (1-in-100 year) design flood event that reflects plausible changes in catchment physical parameters in the 2080s. Initial results suggest that a 1-in-100 year storm in the 2080s may be greater in magnitude, rise and recede faster, and be associated with greater depths of flooding than predicted using current flood risk assessment frameworks in the UK. This information could provide new information to help developers choose more sustainable, flood-resistant and resilient designs. [ABSTRACT FROM AUTHOR]

Quantified models of flood risk that incorporate an explicit representation of the performance of flood defence infrastructure are becoming an increasingly important component of efforts to manage flood risk. The models have been applied to support a wide range of decisions, including long-term strategic planning, assessment of investment needs and shorter-term asset management. The model currently applied in practice by the Environment Agency in England and Wales makes a number of simplifying assumptions to achieve computationally practical run-times. One of these simplifications relates to the volume-based flood-spreading algorithm that is applied. This paper describes the implementation of a new time-based inundation model within the existing risk analysis modelling approach. The new inundation model offers a significant increase in the representation of the physical processes within the flood simulation component of the risk analysis model. It also offers new outputs in terms of estimates of maximum depths and flood velocities. Velocities are known to be an important factor in flood-related fatalities. A simplified method to estimate life-loss has been combined with new output from the improved inundation model to illustrate how estimates of risk to life could be provided. [ABSTRACT FROM AUTHOR]

Early researchers recognised that the long-established Muskingum hydrologic routing model's parameters vary with flood characteristics, but no methods were developed to account for this variation. Such methods would have made the model too complex to solve using prevailing technical knowledge. This paper presents a versatile non-linear Muskingum model with four variable parameters; each is represented by a two-step function of a dimensionless inflow variable, so the model thus has eight parameters. The model is general and produces a wide array of 15 special models with the number of parameters ranging from four to seven. The routing procedure is based on the modified Euler method. Three examples with different hydrograph types were used to evaluate model performance. Based on the application results, guidelines for model selection for different hydrograph types are presented. The recommended models have four to six parameters and substantially improve model performance for predicting flood flows compared with the traditional three-parameter model. This research continues to promote alternative thinking to improve model performance by modifying model structure, instead of the solution algorithm. [ABSTRACT FROM AUTHOR]

This paper employs non-linear programming, genetic algorithms and fixed-length gene genetic programming (FLGGP) for the real-time operation of a three-reservoir system (Karoon4, Khersan1 and Karoon3) in which dependent and independent approaches are used to forecast the hydroelectric energy generated by the system. A total deficiency function as well as efficiency criteria are used to investigate the results obtained. The latter indicate that the more flexible FLGGP gives the most efficient function for the extraction of reservoir operation rules in both dependent and independent approaches. By comparing the two approaches, no significant difference was observed. Consequently, due to the simplicity of the application of the forecast-independent approach, it is suggested for application in the extraction of reservoir operation decision rules. Moreover, the advantages of a three-reservoir system operation over a single-reservoir system operation reflect the efficiency of the integrated management of water resource systems. [ABSTRACT FROM AUTHOR]

Pier scour is a significant problem affecting the safety of bridges. For given hydraulic and geometric conditions, accurate prediction of scour with non-uniform sediments is important, but this need has not been fulfilled. The purpose of this research was to develop a three-dimensional model for scour prediction and to verify the model using laboratory measurements. The model allows for selective transport of non-uniform sediments, particle hiding and bed-level change in response to scour and deposition. The development of scouring around a circular pier on a mobile channel bed with non-uniform sediments was successfully predicted and scour depth prediction agreed well with the measurements. It was found that scour patterns emerge from the lateral sides of the pier and migrate towards its upstream nose. Upstream of the pier, strong downflow and vortex motions develop and effectively remove sediments from the foot of the pier; at equilibrium, the bed-surface slope almost reaches the angle of repose of sediments. On the upstream side, the scour hole has the shape of almost half a cone. Grain size non-uniformity reduces the magnitude of scour. These findings are of relevance to the safe and cost-effective design of pier foundations. The modelling techniques are computationally efficient and are useful for field-scale application. [ABSTRACT FROM AUTHOR]

A coupled one-dimensional (1D) and two-dimensional (2D) numerical model for free-surface flows is presented. For the 1D model, the finite-difference method is used to discretize the Saint-Venant equations. An implicit dual time-stepping method is applied to a finite-volume model for 2D flows to improve run-time efficiency. Four test cases - one extensive analytical benchmark case, two linking examples and a dam break with actual topography - are applied to validate the proposed model and to demonstrate its performance in comparison with an explicit scheme and published results. The proposed model was found to be accurate and efficient for simulating free-surface flows in practical applications. Two treatment methods for dealing with the boundary of the 2D model at the coupled area are also compared. The results show that using exchange water as a source term is a more stable treatment than as an open flow boundary, with only a small difference in simulation results. [ABSTRACT FROM AUTHOR]

Results of a computational fluid dynamics (CFD) study of flow, transport processes and pathogen inactivation in contact tanks are presented. The three-dimensional numerical simulations are first validated using data from a previously completed laboratory experiment and velocity and conservative tracer transport data are available for comparison. The good agreement between CFD and experimental data confirms that the model reproduces accurately hydrodynamics and tracer transport processes. The analysis of the results reveals that the flow in the tank features extensive three-dimensionality, which is attributed to the current inlet configuration. Pathogen inactivation simulations show that complex flow in the tank affects the disinfection performance negatively. The potential for tank optimisation is examined by way of additional simulations featuring varying inlet designs, where it is shown that optimisation of inlet condition enhances the performance of the tank in terms of pathogen inactivation level for the same disinfectant dosage or the possibility of disinfectant dosage reduction towards reduced disinfection by-product production. [ABSTRACT FROM AUTHOR]

The water resource of the Blue Nile River in north Africa is under increasing pressure due to rapid population growth and economic development. The situation is aggravated by a lack of coordinated management and governance, partly caused by incomplete knowledge of the water supplies, uses and needs. Proper water management is particularly important now, considering the recently completed and planned mega dams on the Blue Nile River network. This paper reports on the construction of a one-dimensional hydrodynamic model covering the entire Blue Nile River system, from Lake Tana to the confluence with the White Nile, with the aim of quantifying water availability throughout the year, for different conditions. The work included an extensive field measurement campaign along the Blue River and its tributaries, both in Ethiopia and Sudan. Calibrated and validated with independent datasets, the model was used to quantify water uses in the period 2008-2010, which were then compared with the official figures. The results show that the dry season is characterised by extra water losses that should be taken into account when quantifying water needs, especially during the filling up phase of new reservoirs. [ABSTRACT FROM AUTHOR]