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Aristotle University Of Thessaloniki (AUTH) (2007)

Critical review of the groundwater modeling process in GIS environment : : implementation of mathematical models in ground sustainable management

Καβαλιεράτου Σοφία

Titre : Critical review of the groundwater modeling process in GIS environment : implementation of mathematical models in ground sustainable management

Auteur : Καβαλιεράτου Σοφία

Grade : Doctor of Philosophy (PhD) 2007

Université de soutenance : Aristotle University Of Thessaloniki (AUTH)

Résumé partiel
The objective of this dissertation is a critical review of all the required stages for the development of a sound groundwater mathematical model. Towards this objective a groundwater model is developed and implemented for the management of the Pieria aquifer, Greece. The stages of the modeling process which are analyzed in this dissertation are the following : - development of the conceptual model, - construction of the numerical model, which includes the definition of the space and time discretization, the initial and boundary conditions, the recharge and discharge of the system, the representation of hydrogeologic features of the system, the spatial structure of the aquifer’s hydrogeologic parameters, the selection of the method for the solution of the groundwater flow equation and the convergence criteria for this method, - calibration of the model, - evaluation of the model, - sensitivity analysis, - validation of the calibrated model and – application of the model to predict the system’s response under various conditions. The model which was developed for the Pieria aquifer is a two-dimensional transient flow model. It covers an area of 256 km² and it has 1759 active cells, with a size of 350 m x 350 m each. Software packages which were used for the construction of the model are : MODFLOW 2000, Argus ONE, ArcGIS and PEST. The zonation method was used for the description of the hydrogeologic parameters’ spatial variability. The grid was divided in 11 zones of uniform hydraulic conductivity in the x-direction, 6 zones of uniform horizontal anisotropy, 4 zones of uniform specific storage and 4 zones of uniform specific yield. The values of the 25 hydrogeologic parameters resulted from the calibration process. The model was calibrated against 1173 piezometric head observations and 26 spring flow observations with the Gauss-Levenberg-Marquardt method. The piezometric head and the spring flow observations were collected from September 1992 to April 1995, on a monthly basis. Both qualitative and quantitative criteria were used for the evaluation of the calibrated model. The results which we obtained show that the model represents adequately the simulated system. The effect of each one of the 38 model parameters (25 hydrogeologic and 13 recharge parameters) was examined with the sensitivity analysis process. A second set of monthly data (118 head observations and 4 spring discharge observations, from May 1995 to August 1995 were used for the validation of the calibrated model. The validation process verified that the calibrated model describes accurately the water dynamics of the Pieria aquifer. Finally, the calibrated model was applied for a period of 3 years to assess the consequences of two pumping scenarios concerning the location of irrigation wells. The proper time discretization was examined by using a number of uniform and geometrically increased time steps. The comparison of total execution time and computed heads revealed that increasing the length of the time step geometrically, can reduce execution time significantly, but the corresponding heads diverge from those computed with uniform time steps. It is concluded that the time discretization depends on the special characteristics of the model and must be investigated thoroughly in any groundwater mathematical model. The initial condition of the computations must be also examined very carefully. An arbitrarily defined initial condition (i.e. interpolation from field measurements), sometimes can influence the results until the end of the whole simulation period.

Mots clé : Ground water modeling process ; Aquifer management scenarios ; Known head boundary condition ; Groundwater model calibration ; Sensitivity analysis ; Groundwater model evaluation ; Groundwater model validation ; Modflow pest GIS ;

Présentation (National Archive of PhD)

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Page publiée le 7 octobre 2010, mise à jour le 13 mars 2020