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Modelling perched groundwater by using different numerical solution techniques

Tony Tronnier1
1 Institut für Geologie, TU Bergakademie Freiberg

P 15.7 in Forum Junge Hydrogeologen (H 36, NW III)

Modelling perched groundwater in a graben structure is investigated by a software comparison. Therefore conceptual site models are established. The array of modeling reaches numerical finite difference, finite elements and also finite volume approaches. As representative and objective facts pre- and post processing, visualisation as well as accuracy and robustness shall be taken into consideration.

 

Due to dewatering of deeper aquifers in a mining area, multiple level of groundwater bearing horizons are shifted to unsaturated zones. Near surface groundwater is not affected based on bowl structure of the upper aquiclude. Dewatered underground structures may cause dry cells in modelling programs. As example, MODFLOW-2000 (McDonald & Harbaugh) allows to rewet cells and then reintroduce them into the solution during next iteration. Thereby numerical instability and convergence issues may appear. So cells shall be preserved from getting dry (McDonald et al. 1992).

 

Software applicability for modeling vadose zone and perched groundwater was examined in several field studies and with regard to different MODFLOW code extensions (Bedekar et al., 2012; Kumar et al., 2008; Panday et al., 2008; Jackson et al., 2005; McDonald and Harbaugh). Also non integrated codes and theoretical approaches are carried out (Sailhac et al., 2009; Panday et al., 1993; Velasquez et al., 2007; Malama et al., 2007).

 

For accurate modelling of groundwater behaviour close to nature approaches are provided. Furthermore comparable hydrogeological technical contributions as described in Carter et al. (2012); Sailhac et al. (2009) and Hernández et al. (2012) are studied. Later, input data are processed for software comparison. Different numerical approaches as mentioned before are confronted.

 

By using a code extension for the standard MODFLOW-2000 code all three chosen programs (MODFLOW (McDonald & Harbaugh), FEFLOW (DHI-WASY GmbH), PCGEOFIM (Ingenieurbüro für Grundwasser GmbH)) are able to reproduce and handle prescribed situation.

 

The presented work can be seen as a summary for modelling perched aquifers and as basic application of different numerical codes for modeling stated task. The work could be a guideline for decision-making process and also for inexperienced modellers with respect to presented topic.



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Letzte Änderung 01.11.2013