Journal of Water Resource and Protection, 2012, 4, 657-662 doi:10.4236/jwarp.2012.48076 Published Online August 2012 (http://www.SciRP.org/journal/jwarp) Analytical and Numerical Modeling of Flow in a Fractured Gneiss Aquifer Ramadan Abdelaziz, Broder J. Merkel Department for Geology, Technische Universität Bergakademie Freiberg, Freiberg, Germany Email: ramawaad@gmail.com, merkel@geo.tu-freiberg.de Received May 16, 2012; revised June 22, 2012; accepted July 2, 2012 ABSTRACT Investigating and modeling fluid flow in fractured aquifers is a challenge. This study presents the results of a series of packer tests conducted in a fractured aquifer in Freiberg, Germany, where gneiss is the dominant rock type. Two meth- ods were applied to acquire hydraulic properties from the packer tests: analytical and numerical modeling. MLU (Multi-Layer Unsteady state) for Windows is the analytical model that was applied. ANSYS-FLOTRAN was used to build a two-dimensional numerical model of the geometry of the layered aquifer. A reasonable match between experi- mental data and simulated data was achieved with the 2D numerical model while the solution from the analytical model revealed significant deviations with respect to direction. Keywords: Ansys/Flotran; MLU for Windows; Gneiss; Packer Test; Fractured Aquifer 1. Introduction Fractured aquifers are very important for groundwater supply because about 75% of the earth’s surface consists of fractured aquifers [1] and 25% of the global popula- tion is supplied by karst waters [2]. Flow velocity in fractured gneiss is known to be highly variable over a range of scales and uncertainties which arises from het- erogeneous flow pattern in fissures and fractures. This has significant implications on water resource manage- ment from borehole to catchment scales. In addition, understanding flow heterogeneity in the aquifer is of great importance for groundwater protection and for pre- dicting contaminant transport. Theis [3] was the first scientist to conduct a transient analysis of the groundwater flow. After Theis, many re- searchers like Warren and Root [4], Kazemi [5], Odeh [6], Hantusch and Thomas [7], and Streltsova [8] studied the flow through fractured rocks in the context of petro- leum and groundwater engineering. Jenkins and Prentice [9] described groundwater flow in a single fracture with a very large permeability. Sen [10] used an analytical solu- tion to analyze fractured gneiss with a linear flow pattern. Cohen [11] used a two-dimensional numerical model to analyze an open-well test in fractured crystalline rock. Gernand and Heidtman [12] used the analytical model by Jenkins and Prentice to analyze a pumping test in a frac- tured gneiss aquifer. Schweisinger et al. [13] analyzed transient changes in a fracture aperture during hydraulic well tests in fractured gneiss. Wang and Cui [14] ana- lyzed fluid flow and heat transfer by using the distributed resistance application in ANSYS FLOTRAN. Their analy- sis was done without comparing the modeled results with those from experiments (Gu et al. [15] and Cen and Chi [16]). Slack [17] proposed a theoretical analysis for the slug test which couples elastic deformation with fluid flow within a fracture. Molina-Aiz et al. [18] used ANYS FLOTRAN to simulate the velocity and temperature in a ventilated greenhouse. Crandall et al. [19] used ANSYS FLUENT to obtain the flow solution in a fractured aqui- fer. Several analytical solutions are implemented in soft- ware packages like AQTESOLV, Aquifer Win32, Aqui- ferTest Pro, StepMaster, and MODPUMP to determine the hydraulic parameters of aquifers. Some of these packages offer analytical solutions for fractured aquifers. However, these software packages have certain limita- tions due to the more or less arbitrary selection of ana- lytical solutions that are implemented. MLU for Win- dows [20] is based on a completely different concept: It is a multi-layer analytical model for confined and uncon- fined aquifers and can thus be used for any kind of groundwater testing scenario. Several numerical models have been developed to si- mulate the flow and transport in fractured aquifers. Ex- amples are GeoSys/Rockflow and TOUGH2. Walsh et al. [21] modeled flow and mechanical deformation in frac- tured rock using Rockflow/GeoSys. McDermott et al. [22], Myrttinen et al. [23] and others used the numerical simulator GeoSys/Rockflow to simulate the flow and Copyright © 2012 SciRes. JWARP