Stopovaci zkousky na krasovem systemu Zrcadlova koza u Turnova (piscite vapence jizerskeho souvrstvi)

A series of 4 repeated tracer tests was carried out at never before investigated area of Zrcadlová koza near the town of Turnov (Fig. 1). This area consists of a single sinkhole located in a small stream and several springs above and below the path bordering the left bank of the Jizera River. A group of small springs and the main spring Pod Myšinou occur in the study area. In one of the tests a special technique was used that enabled a surface diversion of water normally falling into the local karst system. As shown in Fig. 2, I used a plastic sheet along the yellow line to drain the surface water down the valley to reach the Jizera River, thus preventing infiltration into the karst system. Using this technique, the whole karst system temporarily dried up, and then was again flooded so that the flow into a sinkhole could have been fully artificially controlled. Flow rates during the tests ranged from 1.1-2.3 l/s for the sinkhole, and 0.3-1.7 l/s in the main spring Pod Myšinou. The maximum flow velocities ranged between 130-350 m/h, mean flow velocities between 90-160 m/h. The estimated volume of the flooded part of the system corresponds to 12-23 m3, depending on the current flow conditions. This calculation applies to the mean residence time, which is related to a 50 % tracer recovery. Dispersivity (1.7-2.5) increased with increasing flow rate indicating dominating advection transport, while the Peclet number has fallen (232-138). Complete results are shown in Table 1. It turned out that the tracer recovery and its concentration depend on the flow rate, and on the volume of pore spaces in individual vadose and phreatic zones above and below the lowest water table in the system. Bimodal breakthrough curve obtained, due to the use of a special technique, which is described above, allows to detect or locate bifurcation in the system. Otherwise, this bifurcation would not be detected and located. Results of tracer test showed high flow velocity in the Jizera Formation in this area, and the existence of karst conduits in this important aquifer.

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