Journal of Water Resources Planning and Management

A new two-stage iterative methodology is presented for upgrading of single-source water distribution networks to achieve redundancy. In the first stage, the existing network is strengthened using linear programming (LP) for a fixed flow distribution obtained using a model that maximizes flow uniformity by minimizing variance of flows in the distribution network. In the second stage, the performance of the network is assessed under single-pipe failure conditions using a node-flow analysis, and the most critical pipe-failure condition having the maximum deficiency in meeting nodal demands is noted. To also make the network satisfactory during the failure of a critical pipe, a new flow distribution is obtained by removing the critical pipe. Constraints for this new flow distribution along with previous flow distribution are then simultaneously considered in a new LP problem. An improved design of the network is obtained by repeating the first stage. This two-stage methodology is continued until the network becomes capable of meeting demands at all nodes during any single link failure. The proposed methodology is illustrated by upgrading a water main system for redundancy. The results of the application demonstrate that the new methodology is more efficient and less computationally demanding as compared to other methodologies used for upgrading of the illustrative water main system.

Network model detail can influence the accuracy of results from analyses of water distribution systems. Previous work has shown the limitations of skeletonized network models when considering water quality and hydraulic effects. Loss of model detail is potentially less important for aggregated effects such as the systemwide health effects associated with a contamination event, but has received limited attention. The influence of model detail on such effects is examined here by comparing results obtained for contamination events using three large network models and several skeletonized versions of the models. Loss of model detail decreases the accuracy of estimated aggregated adverse effects related to contamination events. It has the potential to have a large negative influence on the results of consequence assessments and the design of contamination warning systems. However, the adverse influence on analysis results can be minimized by restricting attention to high percentile effects (i.e., 95th percentile or higher).

This paper presents an integrated optimization model for designing sewage collection networks. The layout configuration is designed using the loop-by-loop cutting algorithm. Then, the network with a given layout is hydraulically designed to determine sewer diameters, installation depths, and pump specifications. In both design steps, all technical constraints and criteria are systematically satisfied. Thereby, the optimization of sewer systems becomes totally unconstrained for the applied optimization solver. In this problem, the objective function is the network’s construction cost and the decision variables are the parameters of layout generation and sewer specifications. For optimization of the cost function, the tabu search (TS) method as a deterministic combinatorial metaheuristic is developed and coupled to the design solvers. The proposed scheme is able to search adaptively in feasible parts of the problem’s decision space as well as to solve the two subproblems of layout generation and sewer sizing simultaneously. Then the model is applied against a benchmark case study. It is found that using the integrated model, the design of sewer networks becomes computationally more efficient and systematic, and it is a very promising approach to attain the global optima.

This study is primarily concerned with the planning and management of a multipurpose reservoir. An economic stochastic optimization model is developed and solved to maximize the net economic benefits derived from marketed urban and rural water supply, hydropower generation, and nonmarketed lake recreation uses with consideration of stochastic inflows. Unlike most studies including nonmarket benefits, both the value of a single-day visit and the number of visits as functions of lake level. Results show that for Lake Tenkiller, when recreational benefits are included, it is beneficial to maintain high lake levels until mid-August, and then start drawing down for hydropower generation. A sensitivity analysis is also performed with different values of visits and peak electricity prices. The sensitivity analysis results show a benefit gained by managing the lake’s level to protect recreational activities; and that this gain is positive for several different potential scenarios, showing this conclusion is robust.

This paper deals with the optimization of short-term hydropower scheduling when a mathematically feasible solution cannot be achieved. Generally, the numerical search procedure terminates with the detection of infeasibility when an optimization problem is being solved. More often, however, operators of hydropower reservoirs prefer violating the mathematical constraints in order of priority, such that a satisfactory solution to the real-world problem can always be guaranteed. Previous studies rarely addressed this issue in relation to short-term operations of hydropower reservoirs. The present study relaxes the prioritized constraints with extra variables and solves the model by weighted goal programming. The weights are designed such that solving the problem is equivalent to a lexicographical optimization. The solution procedure is also efficient in dealing with large-scale problems using the following techniques: temporal and spatial decomposition of the hydro system, separate solution of plant-based operating zones, and linear programming with nonlinear local searching. The temporal decomposition has a significant advantage in computing time. An iterative procedure that converges fast is proposed to eliminate linearization errors. The model and procedure are applied to deal with the Yunnan provincial hydropower system, which consists of 44 reservoirs, believed to be one of the largest scale problems ever reported.

This paper presents a knowledge-based optimization model for minimizing leakage in water distribution systems through the most effective location and setting of control valves. The optimization model is based on the use of a genetic algorithm (GA), which is known for its robustness for handling the optimization of water distributions networks. Knowledge of the water distribution system has been incorporated into the optimization model to reduce the search space and to enhance the model efficiency in finding the optimal solutions. A single optimization model to search for both the optimal location of valves and their settings has been used. These two improvements over other models have enhanced the efficiency of the model and improved the search for the optimum solution. The model has been used to test leakage minimization in a benchmark water network studied by other researchers and has proven to be very efficient and robust.

The Mekong River Basin in Southeast Asia is undergoing rapid development in the exploitation of its water resources. Although hydropower is the most dominant driver for water development, the possibilities for multipurpose reservoirs have been increasingly discussed but not well studied. The authors assess the potential benefits and negative impacts of a multipurpose reservoir cascade facilitating hydropower and irrigation in the Sesan River, a transboundary tributary of the Mekong. A model-based assessment approach was developed where the hydropower operations of a cascade of reservoirs were simulated together with the irrigation water withdrawals. The assessment revealed that the reservoirs created considerable irrigation potential (28,348 ha), and the resulting losses for hydropower generation were relatively small ($-1.6\%$). The river flow impacts were significant, but they originated mainly from the hydropower operations. The inclusion of irrigation led to an increased competition of water resources during the dry season. In addition, the assessed hydropower and irrigation development affected negatively protected areas, agriculturally valuable land, and forest cover. Gaps and shortcomings in the model-based assessments of water resources development were further recognized, including this one, concluding that particularly the connection to ecological and social domains remains often weak and needs, therefore, to be strengthened.