S. Liberatore

Optimization of Water Distribution Systems by a Tabu Search Metaheuristic

A Tabu Search optimisation technique is proposed for designing, planning and maintaining water distribution systems. As design and maintenance of pipe networks for water supply distribution require high costs, achieving the highest level of performance of existing networks at minimum costs is mandatory. The problem involves setting a lot of variables, as location and diameters of new pipes, operations on existing pipes, and so on. The domain of variables is discrete in nature, due to the fact that pipes are available with unified dimensions. Furthermore, the objective function to be minimised, i.e., the total cost of the plant, is non linear, non differentiable, highly ill-conditioned, and presents a huge amount of local minima. Recently, increasing attention has been paid to heuristic optimisation techniques, such as genetic algorithms (GA), simulated annealing (SA), and tabu-search (TS) for large combinatorial optimisation problems. In particular, GA has been applied to the problem of designing and maintaining water distribution networks. Results show good performance of the GA in terms of objective function values, but high computation time. One of the most promising approaches to combinatorial optimisation problems is the TS metaheuristic, that showed flexibility and effectiveness in a lot of applications. The aim of this paper is to present a TS based algorithm to the design of water distribution systems, and to demonstrate its validity in this field.

Non Linear Optimization Models in Water Resource Systems

The progress made in past years in large-scale optimization algorithms led to a general interest in the possibility of applying mathematical optimization to real Water Resources Systems (WRS). As it is well known, this kind of problem typically generates computationally expensive models involving a large number of variables and constraints. Planning aspects can be represented by linear optimization models by introducing simplifications and approximations, even if linear assumptions are not strictly adherent to real WRS. In order to reach a more adequate level of adherence to the physical system more detailed models are resolved by taking into account non-linearity in objective function and constraints. An expansion technique interacting between primal and dual mathematical optimization models is proposed. This kind of approach is very useful to formulate trade-off between the dimension of water works, the reliability of the system and the prediction of short falls severity in demands. Moreover, the necessity to introduce system-vulnerability leads to solve a quadratic programming model taking into account additional non-linear costs due to the requirement of well operating during periods of drought. An adequate approach for the planning and maintenance optimization of pipes networks for water supply distribution, would consider the non-linear relations between head-loss in each pipe, its diameter, length and hydraulic property.

Combining water supply and flood control purposes in the Coghinas Basin (Sardinia, Italy)

ABSTRACT The increased level of impact on life and infrastructure and the environment caused by flooding in Sardinia (Italy) has resulted in the need for the Flood Risk Management Plans (FRMP). The FRMP has been developed by Sardinian Region Administration that selected the Coghinas Basin (North Sardinia) as a pilot basin in according with the EU and National legislation. Recently, the European Flood Directive 2007/60/CE has stated that the flood-risk evaluation should include a cost–benefit analysis and an integrated decision-making tool should help optimize operating rules for multipurpose reservoirs, primarily with regard to the mitigation of flood risks and high priority demand supplies, and selected flood control works. The main purpose of this study was to develop an integrated flood management model to predict flood inundation in the flood-prone areas for various probabilities of occurrence, identify the flood operating rules in a multipurpose reservoir which accomplish a reduction in flood risk, and assess the total damage due to flooding. The FRMP is currently assessing the impacts of new reservoir operating rules reservoir and new works for flood damage mitigation. Based on a calibrated benefit–cost analysis, the proposed model suggested the best scenario of reservoir operating rules and flood control works with a significant saving of money compared to the actual scenario in the FRMP.

Computational Comparison AmongSome LP Codes For Large Scale WaterResource Optimization Problems

Water resource system optimization problems are characterized by large-scale mathematical models. In this paper we approach a linear approximation of the problem with the aim of comparing general purpose highly-efficient computational public-domain software as well as commercial codes. While comparing, we take into account different size water systems and different sizes of design and management constraints.