A Method for Automatic Detection and Delineation of Karst Depressions and Hills

Karst depressions of decametric scale (dolines, uvalas, poljes, and other endorheic basins) play an important role in the hydrogeology of karst aquifers. They are traps of sediment and when their detritic filling has an important thickness they can retain a large amount of water delaying their percolation towards the water table or towards the networks of conduits. Many times the delineation of the depressions may be difficult because the study area may be very large, or inaccessible or hidden by vegetation. In those circumstances, it is of great help to have an automatic method of depression detection and delineation. The proposed procedure uses the digital elevation model, a geographical information system, an algorithm of pit removal and basic operations of map algebra. The method provides the depth of each detected depression measured from its rim. This fact can be used to detect the center of maximum depth as well as for calculating morphometric parameters using depth. The final map of depressions can be characterized by altitude in order to have morphometric parameters related with elevation. The algorithm has been extended for detection and delineation of karst hills. The methodology is illustrated with the Sierra de las Nieves karst aquifer in the province of Malaga, Southern Spain, where the depressions and hills show a strong structural control.