Y. Mylopoulos

A Stochastic Optimization Approach in the Design of an Aquifer Remediation under Hydrogeologic Uncertainty

A stochastic optimization approach is presented for the remediation design of a contaminated aquifer with limited hydrogeologic information. Stochastic simulation using the Monte Carlo technique, produces a series of equally probable realisations of the spatially varying random hydraulic conductivity field. The stochastic flow and transport simulation model is coupled, using the response matrix approach, with a nonlinear optimization algorithm. The whole process is integrated into an algorithm which is effectively applied in the case study of the Kalamaria aquifer, Chalkidiki, Greece. The stochastic optimization procedure is followed by a reliability analysis, giving useful information to the decision makers concerning the effectiveness of the optimal results.

Evaluating demand management aspects of urban water policy—A field survey in the city of Thessaloniki, Greece

Abstract The objective of the paper is to investigate the attitudes and preferences of the residential water users of the city of Thessaloniki, in order to evaluate the demand management aspects of the urban water policy. A field survey has been conducted in the city of Thessaloniki and investigated among others the reliability of the utility’s services and infrastructure, the acceptability of various water demand options, the willingness to pay of the consumers and the level of public awareness. Straightforward comparisons with the results of a similar survey five years ago help extract useful remarks and conclusions concerning the shift of the urban water policy towards integrated and therefore more sustainable directions.

Modeling Residential Water Demand Using Household Data: A Cubic Approach

Abstract A cubic functional form of an econometric model for residential water demand estimation is used in order to accommodate different price elasticities for different levels of water demand. Precise estimates of these different price elasticities offer a useful tool to water authorities for urban water demand management through price-based policies. Panel estimation methods (fixed and random effects) are employed to estimate model parameters. The results show that a cubic form of the demand equation can provide appropriate estimates of price elasticities for different “consumption groups” of residential customers. In addition, the effect of public awareness and information on water conservation is also evaluated after controlling other parameters affecting demand for water. Thus, another implication of this study is that well-informed consumers, aware of issues of water conservation and of techniques for water efficient use, may be more inclined to reduce their water consumption.

Contribution to the ecological quality of Aliakmon river (Macedonia, Greece): a multivariate approach

In the present study, an attempt was made to estimate the water quality of Aliakmon river using five biotic scores (based on benthic macroinvertebrates), physicochemical variables and multivariate data analyzes. Benthic and chemical samples were obtained from 20 sites, during the low flow season (September, 1995). Benthic macroinvertebrates were collected with the three minute kick-sweep method and several physicochemical parameters (D.O., pH, temperature, nutrients etc.) were measured. The multivariate techniques FUZZY and CANOCO were applied to the data. Aliakmon river appeared to have poorer water quality during the low flow season than during the high flow season as determined by comparison with a previous survey undertaken in April 1995. The upstream sites had better water quality than the downstream sites. The performance of the biotic scores was generally satisfactory, but in some cases they were deficient in distinguishing between running waters of good and excellent water quality. On the contrary, the multifactorial analyzes, which consider the abundance of the taxonomic groups, appeared to be more appropriate for the classification of the sites based on the structure of their biocommunities.

Analytical solutions for two-dimensional chemical transport in aquifers

Abstract A method of obtaining analytical solutions for chemical transport in two-dimensional aquifers is presented. Assuming a constant velocity field, linear adsorption, and first-order decay the solution is obtained by integrating the solution of a modified one-dimensional differential equation. The procedure is simple and straightforward and can be applied to various sets of initial and boundary conditions as long as the corresponding one-dimensional transport equation has an analytical solution.

Simulation modeling of runoff, groundwater flow and sediment transport into Kastoria Lake, Greece

Kastoria Lake is located in northwestern Greece. The whole basin of the lake is about 253 km2. For the computation of the surface water volume inflowing into the lake from the main streams of the sub-basins located around Kastoria Lake, a rainfall-runoff sub-model is used. A quasi-three-dimensional simulation model of the Kastoria basin aquifer is also realized, in order to estimate the groundwater contribution to the volumetric budget of the lake and the whole basin as well. For the computation of sediment load inflowing into the lake from the main streams of the sub-basins, the rainfall-runoff sub-model is combinedwith a soil erosion sub-model and a sediment transport sub-model for streams. A GIS was developed in the hydrologic basin with all data needed for parameter identification and model application. The data base was enriched by a series of on site measurements of water discharge made in all main streams for one whole hydrologic year. By means of the resulting mathematical sediment model, those sub-basins, which deliver most sediment load to the lake, are identified. On the basis of this identification, a series of control measures, for the reduction of sediment inflowing into the lake, at certain places of the above mentioned sub-basins is proposed.

Urban water management in Greece present conditions and perspectives of sustainability

Abstract Greece, a developing Mediterranean country in Southeastern Europe, faces serious water problems. A series of geomorphological, meteorological, and hydrological conditions, in addition to the particular social, economic, and administrative circumstances are currently making sustainable water management a rather complex, difficult, and frustrating task. Present water resource management practices have proven insufficient to integrate both socio-economic development and environmental ecosystem integrity. The results of a survey on the economic and demand management aspects of the urban water policy in Greece are presented and evaluated in this paper. Water shortages, which occur mainly during the summer and especially on the islands, high water consumption rates, a wide variety of water pricing policies, lack of public participation, sectoral and fragmented rather than integrated water management, and the fact that water is considered to be a social commodity are only some of the findings of the survey. The present situation is evaluated and discussed, and the perspectives of a new, demand-oriented urban water management are investigated in an effort to shift urban water policy in Greece towards sustainability.

A sensitivity analysis and parametric study for the evaluation of the optimal management of a contaminated aquifer

A typical groundwater remedation problem is studied by using a combined simulation-optimization model. The management procedure employs groundwater flow and contaminant transport simulation models in conjunction with linear and quadratic programming techniques. The methodology is applied to the hydrodynamic control of a contaminant plume that has to be stabilized and removed by a system of pumping wells. The paper focuses mainly upon a sensitivity analysis to the aquifer transmissivity. The effect of changes in the transmissivities of a zoned aquifer upon the optimal solutions of the management problem is examined by considering the optimal pumping rates, the time to remediation and the pumped groundwater volume as the key output variables of the remediation strategies. In addition, the influence of the dispersivities and the imposed hydraulic gradient upon the same output variables is critically evaluated. The results of the study illustrate the need for uncertainty reduction in the knowledge of the hydrogeologic parameters.

Risk-Based Decision Analysis in the Design of Water Supply Projects

The application of a decision analysis methodology to a small-scale water-supply/aquifer-contamination problem is presented. The main characteristic of the study is the development of a series of alternative strategies to ensure a continuous water supply to a village under variable risk conditions. It is assumed that the risks involved in the analysis reflect the uncertainty as to the hydraulic conductivity. Thus, a stochastic simulation model for groundwater flow and contaminant transport is employed in order to evaluate the implications of uncertainty in the systems behaviour upon the overall design decisions. Alternative decision strategies are formulated by considering both actual and probabilistic costs, and they are finally compared using a risk–cost–benefit objective function.

A Combined Use of Simulation and Optimization Techniques in the Solution of Aquifer Restoration Problems

A computational procedure for contaminated aquifer restoration is described. The methodology comprises a combined use of groundwater flow and solute transport simulation models with nonlinear optimization. The planning procedure concerns the stabilization of a contaminant plume and the removal and treatment of the contaminated water by simultaneously operating a system of pumping and injection wells and a treatment plant. The stabilization is controlled by imposing hydraulic gradient constraints close to the plume boundary, the location of which is periodically being updated through successive applications of the solute transport model. The efficiency of the cleanup process is assumed to be directly related to the treatment cost of the pumped water. Thus, a sequential optimization procedure is being applied, where treatment costs are minimized for specified periods of time, at the end of which the effectiveness of the pumping strategy is checked through the determination of the shrinking plume’s new geometry. In the paper this design methodology is described along with an example on a hypothetical aquifer. Numerical results are presented which show the impact of various management decisions on the overall efficiency of the cleanup procedure.