Karst Waters

Abstract

It is important to determine the directions and characteristics of the underground water flow from the area of the planned railway line towards karst springs within its impact area. In this chapter hydrogeological characteristics of the karst section, known directions and characteristics of the underground water flow, bacteriological indicators and hydrological conditions, and risk for contamination of karst water in the study area are presented. The main paths of the groundwater flow are directed towards the springs of the Timava, Rižana, Osapska reka and Boljunec springs. An important additional information on the courses and characteristics of the underground water flow in the karst was obtained by applying a tracer test method, which monitored transfer of the injected tracer (water-soluble substances, harmless to the environment) through the aquifer. The spreading tracers also point to peculiarities of the functioning of karst aquifers in which waters flow out from a specific spot towards various springs in several directions; the underground pathways and the location of the watersheds between the catchment areas of individual springs change depending on the hydrological conditions. Faecal contamination of springs, especially those that are used for human consumption, represents a serious epidemiologic problem. Simultaneously with the tracer experiment at three selected springs (Boljunec, Osapska reka, Rižana), water samples were screened for the presence of bacteriological indicators. The research showed that the springs occasionally had a high concentration of total cultivable bacteria, and that in them isolates indicative of E. coli were also retrieved. Because the construction of railway tunnels through the recharge area of these springs might affect the hydrological conditions of the springs, it is therefore advisable to continue bacteriological monitoring during the construction works. A review of the results of the conducted tracer tests has shown good permeability of karst and a concentrated and fast flow through karst aquifer. So, in light of the described potential endangerment of the above-mentioned water sources, a comprehensive analysis of the quality of the springs should be performed prior to the building works. Within the scope of the research into karst waters, the main objective was to determine directions and characteristics of underground water flow from the area of the planned route towards karst springs within its impact area. It is only based on a good knowledge of these characteristics that one can make an assessment of the probable impacts of the construction and operation of the planned railway line on karst waters, and suggest suitable measures for their protection. The measurements of the levels of groundwater in the area of the route were not part of the karstological research assignment which this text sums up, but part of a special hydrogeological study. Therefore, in Subsection 4.1.3 about the water table in the karst, we state only a few basic data on water levels in karst caves and springs in the broader area, with intention of describing general hydrogeological characteristics. More detailed measurements of the levels were conducted under the comprehensive karstological study of the caves of the contact karst of Beka and Ocizla and are presented in Chap. 5 with a detailed description of this system.