Hydrochemical and Isotopic Checks of Geological and Hydrological Models

Geological models are an independent entity and an essential part of hydrological models. Geological models deal with rock sequences (candi-

Fig. 3.11 A dike intersecting the flow of groundwater and acting as a subsurface dam. The water table is higher on the upstream side, providing a promising site for drilling a well.

date aquifers and aquicludes), rock properties (in terms of their potential influence on the quality of hosted groundwater), existence of preferred flow paths (karstic features, open fractures and faults), identification of subsidence structures, and identification of hydraulic barriers (intrusive bodies and clay or shale squeezed into and around tectonically shaped rock bodies). However, geological data are scarce and of a fragmented nature, seldom leading to a unique model solution. Hence, geological conclusions, or suggestions, should always be checked against hydrochemical and isotopic observations.

Similarly, hydrological models, based on precipitation distribution, topographic relief, location of the terminal base of drainage, hydraulic head data, and geology are also of a fragmented nature and seldom lead to a unique model solution. The situation may be significantly improved by the application of hydrochemical and isotopic checks, as discussed below.

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