Transport characteristics as important of karst evolution

Karst aquifers develop where the dissolution of soluble rocks causes a widening of fractures, thus creating highly permeable solution conduits. Flow velocities in conduits are high and thus residence times of solutes injected into sinkholes or swallets typically short, i.e., in the order of days for transport distances of several kilometres. As a consequence, point-source contaminations may pose serious threads to drinking water supplies relying on karst spring waters. Despite the rapid transport through solution conduits, diffuse-source contaminants such as pesticides are found to be highly persistent in karst aquifers. Long residence times (i.e., many years) are also inferred from the interpretation of environmental tracer data. These observations are in accordance to the well-established conceptual model considering karst aquifers as dual or triple porosity systems, consisting of a matrix/fracture porosity, which provides the majority of storage, as opposed to the conduit porosity, which is much more permeable but makes up only a small percentage of the total porosity. Following this conceptual model, residence times within the matrix/fracture porosity will be much higher than those in the conduit system. This project aims at providing fundamental knowledge about the porosity development and the resulting porosity distribution in soluble rocks as well as its consequences for the transport properties of the aquifers. Generic aquifer models will be obtained by modelling the dissolutional widening of discrete pathways, i.e. the development of conduit porosity. These aquifer models will then be used for studying the transport behaviour of tracers or contaminants. Thus, transport characteristics are considered as imprint of karst evolution. As a result, it will be possible to identify general interrelations between (hydro-)geologic factors governing karst evolution, the resulting porosity distribution, and its implications for the residence time distribution of point-source and diffuse-source contaminants. This knowledge, on the one hand, will be useful for obtaining indications about transport characteristics from readily available field observations, such as structural and lithologic controls or the position of the base level. On the other hand, a significant contribution will be made to the development of methods aiming at inferring aquifer properties from the observed transport behaviour of artificial or natural tracers.

Karst aquifers develop where the dissolution of soluble rocks causes a widening of fractures, thus creating highly permeable solution conduits. Flow velocities in conduits are high and thus residence times of solutes injected into sinkholes or swallets typically short, i.e., in the order of days for transport distances of several kilometres. As a consequence, point-source contaminations may pose serious threads to drinking water supplies relying on karst spring waters. Despite the rapid transport through solution conduits, diffuse-source contaminants such as pesticides are found to be highly persistent in karst aquifers. Long residence times (i.e., many years) are also inferred from the interpretation of environmental tracer data. These observations are in accordance to the well-established conceptual model considering karst aquifers as dual or triple porosity systems, consisting of a matrix/fracture porosity, which provides the majority of storage, as opposed to the conduit porosity, which is much more permeable but makes up only a small percentage of the total porosity. Following this conceptual model, residence times within the matrix/fracture porosity will be much higher than those in the conduit system. This project aims at providing fundamental knowledge about the porosity development and the resulting porosity distribution in soluble rocks as well as its consequences for the transport properties of the aquifers. Generic aquifer models will be obtained by modelling the dissolutional widening of discrete pathways, i.e. the development of conduit porosity. These aquifer models will then be used for studying the transport behaviour of tracers or contaminants. Thus, transport characteristics are considered as imprint of karst evolution. As a result, it will be possible to identify general interrelations between (hydro-)geologic factors governing karst evolution, the resulting porosity distribution, and its implications for the residence time distribution of point-source and diffuse-source contaminants. This knowledge, on the one hand, will be useful for obtaining indications about transport characteristics from readily available field observations, such as structural and lithologic controls or the position of the base level. On the other hand, a significant contribution will be made to the development of methods aiming at inferring aquifer properties from the observed transport behaviour of artificial or natural tracers.