Hidden groundwater inflows from the Slovensky kras Mts. to the Slana River identified by thermometric and resistivimetric measurements

摘要

Longitudinal profile measurement of specific electric conductivity (resistivimetry) and water temperature (thermometry) along the watercourse of a surface stream, if performed in sufficient density of measuring points, can reveal position of hidden groundwater inflows in a surprisingly detailed scale. Contrary to flow accretion survey, i.e. discharge measurements on appropriately distanced locations of streams that are able to quantitatively define hidden surpluses or losses of discharge, but their evaluator can attribute these to stream segments only, outputs of thermometry and resistivimetry have potential of precise location identification of groundwater outlets. The best season for such measurements is culminating summer or winter with naturally highlighted contrast in surface water and groundwater temperatures. In our case, thermometric and resistivimetric measurements were performed on the watercourse of the Slana River (SE Slovakia), segment between Brzotin and Gombasek municipalities, where the river is cutting two major karstic plateaus (Silicka planina and Plesivska planina) in a form of several hundred meters wide and several hundred meters deep canyon. Three major karstic springs are found in this area, but hidden dewatering of karst water resources directly into the Slana River remained unknown. Measurements were performed within 5 summer days from 21/06/2016 until 25/06/2016 on an 8300 meters long rivercourse section. The basic footage step of measurements was 1.0 meter. Mesurements were performed in the streamline of active flow and also along its left and right side, 20 cm aside the stream-bank. Both parameters - water temperature and specific electric conductivity - were measured near the streambed, ~5 cm above the bottom, in the -20 to 40 cm distance from the left or right bank, and also in the main streamline. No major karstic groundwater inlets were found here, but small-scale inflows were mostly found on the left bank pointing to groundwater flow from the east - from the Silicka planina Plateau. It seems that at least on the Brzotin-Gombasek watercourse segment of the Slana River, Plesivska planina Plateau is dewatered only through already registered karstic springs west from the river.