engleski

Groundwater research on a Dinaric karst island – the island of Vis case study (Croatia)

Adriatic karst island of Vis has a public water supply from its own groundwater for decades. First organized water supply is connected with costal spring Pizdica in Komiža bay, where extraction site was dug in a rock in 1950s with the purpose of army water supply in case of nuclear war. The water was also used for Komiža settlement. In late 1960s and 1970s the Korita pumping site was established after a bulk geological, hydrogeological and geophysical research. There are six boreholes (wells) with depths from 145 to 200 m. During establishment, minimal pumping quantities were around 3 L/s on Pizdica and some 27 L/s in Korita. In 1999 new phase of research was performed, and conceptual model of island’s aquifer has been presented. Structural geological, hydrogeological and hydrochemical researches provided the basis of that model and starting point for future sanitary protection of the aquifer. After reinterpretation of former pumping tests it was decided that extraction rates in Korita could be increased up to 40 L/s without quality deterioration. In 2012 the research continued with a tracing experiment, conceptual model was modified and sanitary protection zones delineated. Even though this is a Dinaric karst island, good positioning of Korita pumping site combined with some favorable geological features resulted in long term sustainable public water supply of the whole island. Nevertheless, the water demand will probably increase in the coming years and some additional quantities should be put in use. Considering that, part of the last research phase was targeted on a few locations where more groundwater could be extracted in the future. The main methods used were hydrogeological and geological mapping, as well as the geophysical research (geoelectrical sounding was performed because of the studied depths – over 300 m). Tracing experiment resulted in groundwater velocities determination in complete accordance with previously defined hydraulic conductivity of the rock mass in Korita area. Apparent velocities in main flow direction were approximately 0.27 cm/s and perpendicular to that direction below 0.1 cm/s. Hydraulic conductivity of rock mass in that part of the island is within the order of magnitude of 10-5 m/s. Position of groundwater divide between Korita and Pizdica (sub)catchments was also determined. Four researched micro-locations had different perspective for further hydrogeological research, and one is chosen as possible early warning system monitoring site.

karst aquifer, salt/fresh water relations, sanitary protection zones, tracing experiment

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