Konstantinos Katsifarakis

A multipopulation genetic algorithm to solve the inverse problem in hydrogeology

The inverse problem of groundwater flow is treated with an automatic method that can produce several alternative solutions at once. During their joint optimization, these solutions can exchange information in order to maintain some diversity and thus avoid a systematic premature convergence toward a single local minimum. Although genetic algorithms are capable of doing this, they have not often been used in groundwater inverse optimization. First, a specific multipopulation genetic algorithm is developed. It is then tested on two synthetic cases of steady state flow with transmissivity values extending over 4 orders of magnitude. The first test is nonparametric and optimizes as many parameters as those used to define the reference case. The second test uses a sort of “pilot point” parametrization. The optimization is carried out on a limited number of perturbations that are interpolated and superimposed on an initial transmissivity field. In view of the good quality of the results, these initial attempts provide incentives to further develop genetic algorithms in groundwater inverse problems.

Combined use of BEM and genetic algorithms in groundwater flow and mass transport problems

The boundary element method (BEM) can be used very efficiently, in solving groundwater flow problems. Genetic algorithms (GAs) constitute a very efficient optimization tool. In this paper, BEM and GAs have been combined to find optimal solutions in three classes of commonly encountered groundwater flow and mass transport problems: (a) determination of transmissivities in zoned aquifers (inverse problem), based on a restricted number of field measurements; (b) minimization of pumping cost from any number of wells under various constraints; and (c) hydrodynamic control of a contaminant plume, by means of pumping and injection wells. Application examples show that the proposed combination is very efficient in optimizing development and protection of groundwater resources.

A BOUNDARY ELEMENT AND PARTICLE TRACKING MODEL FOR ADVECTIVE TRANSPORT IN ZONED AQUIFERS

Abstract One of the most crucial factors that affects both the accuracy and efficiency of a groundwater transport model is the flow simulation method which produces the velocity field. This paper presents a boundary element technique that incorporates the zoning approach to allow aquifer heterogeneity. First, the accuracy of the flow model is verified by comparing it with analytic solutions for well-pumping and injection problems. The boundary element flow model is then coupled with a particle tracking procedure for advection-based transport simulation. The combined model also calculates streamlines, travel times and breakthrough curves and is therefore a powerful tool for simulation and management of advection-dominated contamination problems.

A Set of New Benchmark Optimization Problems for Water Resources Management

In this paper, we introduce four new benchmark problems, which are based on rather common optimization issues of water resources management. These problems have the following features: a) adjustable difficulty, to cover a wide range of common engineering problems b) physical background familiar to scientists working on water resources management c) known global optimal solution and known range of values of the objective function d) easy application and e) low computational volume (analytical solution of the respective groundwater flow model). First we calculate the optimal solutions of these problems and then we evaluate their difficulty and their suitability as benchmarking tools, based on theoretical considerations and on the performance of a genetic algorithm and a simulated annealing code in finding their optimal solutions. Results show that the proposed set of benchmark problems is useful for evaluating heuristic optimization codes in the field of water resources management.

OPTIMIZATION OF LOW-ENTHALPY GEOTHERMAL HEATING SCHEMES BY MEANS OF GENETIC ALGORITHMS

The application of genetic algorithms to the optimization of certain aspects of low-enthalpy geothermal district heating schemes is presented. In particular, minimization of the cost due to pumping and amortization of the construction of the pipe network inside the geothermal field is investigated. An outline of the optimization code is given and its performance is evaluated through application examples to geothermal fields with uniform and non-uniform water temperature distribution. In addition, a procedure to decide the number of new wells that should be drilled is discussed. It has been concluded that the use of the proposed technique may result in substantial cost reduction, thus promoting the direct use of geothermal energy.

Planning Water Resources Management in Small Islands. The Case of Kalymnos, Greece

Kalymnos is one of the largest islands of the Dodecanese, a rather dense island complex situated at the southeast corner of Europe. The development potential of the area is large. A serious restrictive factor, though, is fresh water availability. The latter has declined in the last few years, due to increase in population and in per capita water demand. As a result, the already stressed groundwater resources have been overexploited, and salinization of many coastal aquifers has already taken place. Since water import from other areas is not a sustainable solution, optimization of the management of local water resources is necessary.This paper deals with both sides of the water balance of Kalymnos. First an estimate of the evolution of water demand is discussed. The use of a GIS tool, in order to estimate renewable water resources at the hydrologic basin scale, is presented next. Conjunctive use of surface and ground water resources, including traditional rainwater collection, is proposed. Water resources development in the hydrologic basin of Vathy, which is one of the largest of the island, is discussed in more detail.

Solar distillation treatment of landfill leachate. A case study in Greece

Abstract Landfill leachate constitutes a major environmental hazard for surface and groundwater. For this reason it should be collected and properly treated. Solar distillation offers a promising alternative to currently used treatment methods. Simple solar stills seem to be very suitable for this task, as proposed in a study for the disposal of municipal waste of the city of Thessaloniki, Greece.

Minimization of Transient Groundwater Pumping Cost-Analytical and Practical Solutions

In this paper, we study pumping cost minimization for any number and layout of wells under transient groundwater flow conditions in infinite confined aquifers and semi-infinite ones, to which the method of images applies. Moreover, we take into account additional steady-state flow, which is independent of the well system and results in non-horizontal initial hydraulic head level distribution. We prove analytically that, at any time, the instant pumping cost is minimum, when the following condition holds: the observed at that instant differences between hydraulic head values at the locations of the wells are equal to the half of the initial ones, which are due to the additional steady-state flow. Based on this proof, an analytical calculation procedure of the time-dependent optimal distribution of the required total flow rate to the individual wells is also presented. Moreover, as well flow rates usually remain constant over the pumping period, an approximate calculation of the optimal constant well flow rate distribution is outlined, based again on an analytical procedure.

Prediction of flow rate of karstic springs using support vector machines

ABSTRACT Complex void space structure and flow patterns in karstic aquifers render behaviour prediction of karstic springs difficult. Four support vector regression-based models are proposed to predict flow rates from two adjacent karstic springs in Greece (Mai Vryssi and Pera Vryssi). Having no accurate estimates of the groundwater flow pattern, we used four kernels: linear, polynomial, Gaussian radial basis function and exponential radial basis function (ERBF). The data used for training and testing included daily and mean monthly precipitation, and spring flow rates. The support vector machine (SVM) performance depends on hyper-parameters, which were optimized using a grid search approach. Model performance was evaluated using root mean square error and correlation coefficient. Polynomial kernel performed better for Mai Vryssi and the ERBF for Pera Vryssi. All models except one performed better for Pera Vryssi. Our models performed better than generalized regression neural network, radial basis function neural network and ARIMA models.

Combining Pumping Flowrate Maximization from Polluted Aquifers with Cost Minimization

In this paper, we present a methodology for optimal management of aquifers affected by non-conservative pollutants, by means of application examples. Our multi-criteria approach takes into account: a) Maximization of safe total flowrate from a system of wells; and b) Minimization of pumping cost or of pipe network construction cost. As a preliminary step, we have studied maximization of the total safe well flowrate, without cost restrictions, in order to calculate an upper flowrate bound for all application examples. Then, we have solved two sets of minimization problems, using one of the aforementioned cost criteria in the respective objective function and different values of the required total safe well flowrate as a constraint in all of them. In this way, we have derived a set of Pareto optimal solutions for each problem. We have used the method of genetic algorithms as optimization technique and a moving point code for the simulation of advective pollutant transport. Our paper includes also: a) a discussion of relevant technical details, i.e., moving point arrival at production wells and structure of the penalty function, which is used in the genetic algorithm code; and b) a comparison of the results of the two sets of examples, which shows that the optimal well layouts are rather similar for large total safe flowrate values, while they are quite different for small ones.