Approaches for Modelling of Hard Rock Aquifer System

The groundwater flow models so far used represent porous media having continuous interconnected pore space. The flow problem in the fractured rocks has always been a chalIenging one. Evolving conceptual model of a fractured system requires either a gross simplification or a detailed description of the aquifer properties controlling the groundwater flow. At present, there is only a basic conceptual understanding of flow in the vicinity of weathered and fractured hard rock aquifers. NormalIy this conceptual understanding is not translated into the quantitative interpretation procedures. Often, simple continuum models are applied to analyse pumping test data, and the results then used to produce quantitative catculations on a regional scale. Even if the regional system can be represented using the continuum equivalent approach, it is unlikely that the results of applying continuum models at the local scale have any general validity, and the aquifer parameters so derived may be different from the aquifer parameters appropriate for describing regional flow in quantitative terms. Hence, there is a need to develop appropriate methods for analysis of pumping test data and appropriate simulation techniques to improve the success rate and yield of welts in fractured rocks. The analysis should provide cost-benefit analysis for locating new high yield wells. To do this, it is necessary to investigate in detail the flow in the vicinity of a pumping borehofe, and to apply appropriate non-continuum models. This paper reviews the following models viz. (i) equivalent porous medium (EPM), (ii) dual porosity medium, (iii) discrete fracture network (DFN), (iv) stochastic continuum (SC), and (vi) channel network (CN), which are used to conceptualize fractured systems. The utility of integrated DFN and SC modelling approach to simulate fractured aquifer systems is brought out through a case study in Ireland.