Hydrogeological Exploration of the Rječina River Spring in the Dinaric Karst

Abstract

The Rječina spring is one of the major springs in the DinaricKarst. It appears as the contact between permeable carbonate andimpermeable clastic rocks, with a discharge of up to 120 m3/s but itdries up during the dry summer seasons. The spring occurs close tothe town of Rijeka, 325 m above sea level and offers an outstandingopportunity to cover gravitationally the public water demand of atown of about 200,000 inhabitants, and the touristic needs of the wholeregion. This hydrogeological research project is a pan of efforts tosolve the problems of water deficiency during the dry summer seasonsup to a maximum of three months. It was necessary to enter theparts of a karst aquifer that are active even in time of any outflowfrom the Rječina spring by complex geological, hydrogeological andgeophysical exploration accompanied with deep exploratory boreholes.During earlier exploration, it was determined that there are noactive innows in the immediate hinterland of the spring and that it isnecessary to discover the inflows from other karst structures, thatbehave as retentions of karst springs in the zones of permanent discharge.The presence of multiple overthrusted structures in the zonearound the spring site suggest the existence of deep zones of waterretention, which may be reached by an access gallery from theRječina canyon. This work represents a substantial change in theexploration methodology for Dinaric Karst aquifers, because it directsthe researchers toward deep, unknown retention spaces which containlarge reserves of high-quality groundwater outside urban areas.