Stopovaci zkousky na Huberove ponoru (Krystofovo Udoli u Liberce)

Two tracer tests were carried out in the Huber sink in the village of Kryštofovo Údolí near the city of Liberec town, northern part of the Czech Republic. The aim of tracer tests was to verify the flow direction and to characterize the flow and karst conduits. Small lenses of crystalline carbonates are enclosed in quartzite and phyllite in the area of Kryštofovo Údolí. Local karst springs were turned in a water supply network for the Liberec city in 1920, and the Huber sink was sealed to avoid contamination. In 1970s, the existing water supply system was abandoned, and in 1990s the seal of the sink was removed and the stream was reactivated.
Two water works were constructed downstream, and further in the text are called the upper (HV) and the lower (DV), see Fig. 1. The water from HV flows through pipes to DV. Besides the water works there is an abandoned mine with a small outflow of mine water (OD) in the area.
Two tracer tests were performed in the Huber sink, using kitchen salt as a tracer. Tracer concentration was monitored using electric conductivity meters equipped with data loggers (WTW and Solinst devices with conductivity values compensated to constant temperature). Discharges of the sink and springs were measured by filling the vessel, and by dilution method. A Qtracer2 program (Field 2002) was used for analysis of tracer- breakthrough curve.
Quantitative tracer tests showed that water from sink flow into HV (Figs 2-5). The first arrival time was about 5 hours. Maximum velocity was 3 cm/s, mean flow velocity 0.7-1 cm/s. The volume of karst conduits was found to correspond to 34-430 m3, the mean flow area was between 0.07-0.8 m2. Dispersivity was found to be surprisingly high (50-170 m), which indicates that karst conduits are probably filled with detritus, or due to large changes in flow through a cross-sectional area. Water from sink (P) constitutes about 8-20 % of spring flow under normal flow conditions. The rest of water probably comes from diffuse recharge from crystalline rocks enclosing crystalline carbonates.

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