Hydrodynamic dispersion in karstified limestones and dolomites in the Upper Jurassic of the Franconian Alb, F.R.G.

Abstract

In the Upper Jurassic carbonates of the southern Franconian Alb (F.R.G.), groundwater flow is much more pronounced in fissures than in solution channels. With increasing thickness of the aquifer, and with the predominance of dolomitic reef facies, tracer dilution becomes stronger. The evaluation of dispersion in the study area was based on the one-dimensional approximation of tracer transport in the fissured aquifer and considers diffusive tracer exchange between mobile and quasi-stagnant water. The dispersion parameter (1/Pe) was found in each tracer experiment by applying the fitting procedure with the Single Fissure Dispersion Model (SFDM). In solution channels, dispersion seems not to depend significantly upon flow distance. In fissures, however, dispersivities increase comparatively strongly with flow distance. Calculated dispersivities range from 4m in solution channels to some ten meters in fissures. All dispersivities are related to recovery rate, which can be judged as a measure of the draining influence of flow in solution channels on fissure flow. Dispersivities in fissures are lower than in comparable porous media. © 1989.