Groundwater recharge and flow in crystalline formation in Sudety Mts
|Location||International Geological Congress,oslo 2008|
|Holding Date||11 October 2008|
The study here reported was conducted in the Eastern Sudety Mts. (SW Poland) and was concentrated on the identification of groundwater system and the recharge rate evaluation. In the region of study a limited number of wells with low discharge are accompanied by numerous springs. Study area is consist of crystalline hard rock (gneisses, mica schist and granitoids).
In order to solve the problem a field experiment has been conducted in the Snieznik Massif. The experimental field was equipped with a lysimeter, recording the infiltration rate, and daily values of groundwater outflow from an abandoned mine gallery. These measurements were associated with water level fluctuation in an observation well, and the total flow in the Kamienica creek. The recharge rate has been evaluated from three methods: direct measurements with lysimeter, using groundwater level fluctuation method and river hydrograph recession analysis. Annual recharge rate was estimated in wide range as 19%, 39 % and 55 % of total precipitation respectively.
Water chemical composition and concentration of selected isotopes -radon and radium were measured together with tritium, deuterium and oxygen-18. The measurements and results have been interpreted and recharge and discharge model constructed and showed triple zones in the profile of the catchment under study. As a results a three-layer model of hydraulic properties water-bearing zones in hard rocks have been developed. It includes the top layer of a weathering zone, which is mostly composed by sandy clay with thickness from 2, up to 20 m on the valley bottom; the second one is formed of dense fracture network in massif rocks and is present up to 50 meter below land surface. The third one is formed by deep fracture system, reaching the depth of 300-500 m. The top zone is characterised by high water storage (capacity) and relatively low permeability. The second zone shows low storage ability but high transmissivity. The lowest storage and hydraulic parameters are typical of the deep fractured zone, which is the bridge between fresh and mineral water and is reported up to a depth of 500-700 m. An isotopic study of tritium content for years 1992-2000 showed that the mean travel time of tracer equals to 10.4-7.5 years for the exponential and dispersion models, respectively. This could be interpreted as a water residence time in range from 2.0 to 3.5 years for a catchment size of 2000 m. Most of this time is used for travel through the unsaturated zone. The results indicate also a very long residence time of groundwater in the deeper system of water flow. Current study are concentrated on spring data base construction and groundwater quality and quantity verification.