Andrea Sulis

Comparison of generic simulation models for water resource systems

In water resource systems that frequently experience severe droughts, generic simulation models can provide useful information for developing drought mitigation measures. This paper is about modeling in practice rather than in theory. The emphasis is on the application of generic simulation models to a multi-reservoir and multi-use water system in Southern Italy where frequent droughts over the last two decades have necessitated the use of temporary and unsustainable user-supply restrictions. In particular, AQUATOOL (Valencia Polytechnic University), MODSIM (Colorado State University), RIBASIM (DELTARES), WARGI-SIM (University of Cagliari) and WEAP (Stockholm Environmental Institute) models are considered in a preliminary analysis, which considers series and parallel simple schemes and also evaluates the possibility of alternative plans and operating policies in complex real water system. Each model has its own characteristics and uses different approaches to define resources releases from reservoirs and allocation to demand centers. The proposed model comparison and application does not identify in detail all the features of each model, rather it provides insights as to how these generic simulation models implement and evaluate different operating rules.

Short communication: GRID computing approach for multireservoir operating rules with uncertainty

Developing mathematical optimization models that define multireservoir operating rules that are worthy of being evaluated by simulation models is a challenging task. The traditional approach can easily be scaled, and GRID computing can reduce computation times for large water resource systems. The potential for GRID computing in this area of research is largely unexplored. In this paper, the migration of a mixed optimization-simulation approach and preliminary applications to a water system in Southern Italy are presented. Results indicate that GRID computing provides significant savings in computation time.

Trophic State and Toxic Cyanobacteria Density in Optimization Modeling of Multi-Reservoir Water Resource Systems

The definition of a synthetic index for classifying the quality of water bodies is a key aspect in integrated planning and management of water resource systems. In previous works [1,2], a water system optimization modeling approach that requires a single quality index for stored water in reservoirs has been applied to a complex multi-reservoir system. Considering the same modeling field, this paper presents an improved quality index estimated both on the basis of the overall trophic state of the water body and on the basis of the density values of the most potentially toxic Cyanobacteria. The implementation of the index into the optimization model makes it possible to reproduce the conditions limiting water use due to excessive nutrient enrichment in the water body and to the health hazard linked to toxic blooms. The analysis of an extended limnological database (1996–2012) in four reservoirs of the Flumendosa-Campidano system (Sardinia, Italy) provides useful insights into the strengths and limitations of the proposed synthetic index.

Using reservoir trophic-state indexes in optimisation modelling of water-resource systems

Water quality is an important factor to consider when attempting to reconcile mathematical optimisation modelling with the physical reality of water-resource systems. In particular, when the greater part of water resources in supply systems comes from artificial reservoirs, as in Mediterranean regions, a simplified approach based on the attribution of the trophic state of reservoirs can be developed to consider water quality in the optimisation model. Experimental studies have demonstrated that a measure of the trophic state can be given by the Trophic-State Index (TSI), which is evaluated by chlorophyll-a concentration. When certain families of microscopic phytoplanktonic algae produce algal toxins during eutrophication, limitations on resource use based solely on TSI values may be insufficient. In this paper, a linear optimisation model is presented that includes quality indexes estimated based on both TSI and concentration density of the most toxic species of algae in reservoirs. The application of the optimisation model to a multi-reservoir system, located in Sardinia, Italy, highlights the impacts of using different water-quality indexes on the results of the optimisation model.

Mixed Simulation-Optimization Technique for Complex Water Resource System Analysis Under Drought Conditions

The paper illustrates a Decision Support System (DSS) for multi-reservoir water resource systems, named WARGI (Water Resources system optimization aided by Graphical Interface). WARGI was upgraded in the SEDEMED II Project to implement a mixed approach that uses optimization and simulation techniques to select the best combination of proactive and reactive measures under drought conditions. The DSS aims to predict in advance the consequences of management assumptions in a predefined system configuration. The optimization module considers future hydrological and demand scenarios to modify the set of decision variables to be adopted by the simulation module. Lastly, WARGI’s application to the water resource system of Southern Sardinia (Italy) is illustrated.

Reservoirs Water-Quality Characterization for Optimization Modelling Under Drought Conditions Part II – Water-Quality Optimization Modelling

In the southern regions of Mediterranean Europe, the greatest part of water resources for supply systems are derived from artificial reservoirs. A simplified approach to the need of inserting water quality aspects in the mathematical optimization model can be achieved considering the trophic state of reservoirs. In recen91t years, Trophic State Index (TSI) based on Carlson’s (1977) classification appears to have obtained general acceptance as a reasonable manner of classifying stored water in reservoirs; it enables to insert quality constraint in the water management optimization model also considering large size multi-reservoir and multi-user systems. Using TSI index and concentration density values of the most toxic algae, water quality aspects can be easily considered in an optimization model specifically designed for large system management optimization. The usefulness of a mixed quantity-quality optimization approach has been confirmed by WARGI application to a real multi-reservoir water resources system in southern Sardinia

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.

Improved Implicit Stochastic Optimization technique under drought conditions: the case study of Agri–Sinni water system

ABSTRACT In this paper, a methodology is proposed to support water decisions by selecting and evaluating reservoir operating rules (OR) based on hydrological scenarios. The methodology includes optimization and simulation tools within an Implicit Stochastic Optimization (ISO) framework. The paper presents some improvements to the traditional ISO that overcome some limitations affecting previous works. Thanks to the collaboration with Regional Water Authorities in Southern Italy, the proposed methodology, called Modified Implicit Stochastic Optimization (MISO), has been tested in the Agri–Sinni water system. In a participatory and integrated risk management approach to drought events, the reservoir OR defined in the MISO approach based on correlations between releases, storages and inflows performed better than the actual OR in the Agri–Sinni water system and the OR from a simulation-alone procedure. In addition, the user can obtain a significant reduction of computational time by applying the MISO technique in a Grid computing approach.

The Porting of Wargi-DSS to Grid Computing Environment for Drought Plans in Complex Water Systems

The increasing developments in computer technology have motivated the concurrent development of Decision Support Systems (DSSs) aimed at facilitating the planning and management of complex water systems (Assaf et al., 2008). Simulation and optimization models within DSSs provide the main tool for researchers and practitioners to analyze the behavior and performance of any proposed water resource system design or management policy alternative before it is implemented in real systems. Various strategies have been proposed to combine the adherence and flexibility of simulation models with the efficient exploration of mathematical optimization models (Loucks and van Beek, 2005). AQUATOOL (Valencia Polytechnic University) (Andreu et al., 1996), MODSIM (Colorado State University) (Labadie et al., 2000), RIBASIM (DELTARES) (Delft Hydraulics, 2006), WARGI-SIM (University of Cagliari) (Sechi and Sulis, 2009a) and WEAP (Stockholm Environmental Institute) (SEI, 2005) are representative of DSSs used for preliminary analysis of alternative plans and policies. Those popular generic simulation models have been implemented world-wide in a large number of water systems and incorporate most of the desirable attributes of a simulation model. WARGI (WAter Resources Graphical Interface) is a generic DSS for planning and management complex water systems developed at the University of Cagliari (Italy). The DSS is specifically developed to meet the system management requirements to satisfy the growing demands in multi-reservoir systems under water scarcity conditions, as frequently, happen in the Mediterranean regions. Sechi and Sulis (2009a) have recently developed a full integration of the simulation module WARGISIM and the linear optimization module WARGI-OPT in the DSS. This mixed simulationoptimization approach was proposed with the aim of identifying and evaluating mitigation measures in a proactive approach that anticipates the trigger of these actions. The processes that govern the behavior of multireservoir water systems are affected by uncertainty that increases with time and space investigation scales (Simonovic, 2000). Uncertainty is mainly associated with the value of hydrological exogenous inflows and users demand patterns. A common disadvantage of the traditional modeling approach is the large number of system simulations required to achieve acceptable levels of confidence treating data uncertainties in the model. In fact, the proactive approach to drought