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Karst massif susceptibility from rock matrix, fracture and conduit porosities: a case study of the Sierra de las Nieves (Málaga, Spain)

Pardo-Igúzquiza, Eulogio, Durán, Juan José, Luque-Espinar, Juan A., Robledo-Ardila, Pedro A., Martos-Rosillo, Sergio, Guardiola-Albert, Carolina, Pedrera, Antonio
Environmental earth sciences 2015 v.74 no.12 pp. 7583-7592
aquifers, case studies, geostatistics, karsts, porosity, probabilistic models, Spain
The potential contamination of a karst massif from surface sources can be evaluated and represented in a susceptibility map. In the case of a carbonate aquifer, the susceptibility assessment must take into account their very complex and heterogeneous nature. The complexity originates in the presence of three types of porosity: matrix rock, fracture and conduit porosity. This paper presents a method for karst susceptibility mapping by estimating the three porosity types and evaluates their integration in a single susceptibility index. Matrix rock porosity is measured in the laboratory from samples collected in the field and is well correlated with lithology. Fracture porosity is estimated from fracture mapping and field measurements of secondary fracture porosity. Geostatistical methods are used to obtain continuous fields of rock matrix porosity and fracture porosity. Conduit porosity is calculated from a power model fitted to speleological cave mapping data. However, because of the scarcity and sampling bias of conduit data, probabilistic models are conjectured. A fourth porosity factor evaluated is the detritic filling of karst depressions. The integration of the different porosities in a single susceptibility factor gives a quantitative map that is reclassified to provide a qualitative, easy to interpret susceptibility index map of the karst system. Porosity estimation may also be of interest in recharge estimation and mathematical modelling of flow and transport in karst systems. The case study used to illustrate this approach is the Sierra de las Nieves karstified rock mass, a high relief Mediterranean karst in the province of Málaga in southern Spain.