New data on the Svatý Jan pod Skalou karst springs and possible causes of extremely low flow rate of the Loděnice Stream in 2018 and 2019
Abstract
racer and hydraulic tests were used to characterize karst conduits between the Vývěr nad Klášterem Cave and three springs at Svatý Jan pod Skalou. Tracer injected in the cave reached the springs in 30-99 minutes, with the fastest response in the Ivanka Spring, and the slowest in the Kotelna Spring.
The volume of mobile water between the cave and the prings was about 80 m3. The yield of the Ivan Spring dropped 10 mi- nutes after the onset of pumping in the cave which indicates that water partly flows in phreatic conditions.
Extremely low flow rate of the Loděnice Stream at Loděnice (0.07 l/s/km2) in the dry years 2018 and 2019 were not caused by water abstraction in the watershed but by intense vaporation from ponds (average evaporation rate above 100 l/s in the ummer of 2018) and from riparian vegetation. Under such conditions, arst springs contributed to the flow rate of the Loděnice Stream by more han 50 % downstream of Svatý Jan pod Skalou.
At that time, the yield f the Svatý Jan pod Skalou Springs was 17-19 l/s and that of the V nivě Spring was 5-6 l/s.