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| Titel |
Transit time estimation of tunnel inflow in fractured granites |
| VerfasserIn |
A. Balvín, M. Hokr, M. Šanda, T. Vitvar, P. Rálek |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250067480
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| Zusammenfassung |
| We study the water flow from surface to a tunnel in the average depth of 100 m to evaluate the
water residence times in the fractured rock. Transport of 2H and 18O in groundwater was
simulated by use of the lumped parameter approach. The area of interest is located in the
Jizera Mountains near the Bedrichov municipality in the northern part of the Czech
Republic.
Input concentrations of 2H and 18O were measured at UhlíÅská experimental catchment
in a 5km distance from the tunnel. The output concentrations were measured in the water
supply tunnel near BedÅichov. The tunnel is built in compact granite, it is 2600Â m long and
has a maximal depth of 150Â m. The samples were taken from seven different groundwater
seepage sites and from the channel collecting all inflow to the tunnel, in 14 days
intervals in the period from February 2010 to present. The groundwater discharges
were distinguished by their intensity – three dripping ones and four with continual
fluxes.
The residence times of the inflowing water were estimated with the dispersion model in
the FLOWPC simulation program and cover the range of 2010-2011 years. In addition, we
have made preliminary tests with “filtering” the infiltrated concentration data, e.g. assumption
of larger ratio of winter infiltration, time shift between snowfall and snowmelt and use of soil
water sampling instead of precipitation for the input. The best fit was achieved for spring V7
(for deuterium 2H: water residence time TÂ =Â 23.6 months, apparent dispersion parameter
Pd = 0.28 and Nash-Sutcliffe coefficient 80.3 % and for oxygen 18O: T = 30.9 months,
Pd = 0.488 and N-S = 80.1 %, both for redistribution of rain), other fits were
approximately 50-65 % (spring V6: T = 24.9 months, Pd = 0.26, N-S = 61.77 %;
spring V1: T = 28.6 months, Pd = 0.24, N-S = 50.09 %, both for oxygen 18O).
The discharge in the shallow part of the tunnel is probably supplied by flow on
the soil-bedrock interface, with a quick reaction to precipitation and dry in the
remaining periods. Another type of inflow in the shallow part but in compact rock
exhibits a very stable flow and quite stable gradually changing isotopic content.
Several springs are probably supplied along a fracture with high velocity of water
flow.
The outcomes of the application of this method contribute to the assessment of water flow
through the fractured structures up to 150 m deep below the surface.
Acknowledgement: This work has been supported by Ministry of Industry and Trade
within the research project FR-TI3/579, by the IAEA contract 16335, and by Radioactive
Waste Repository Authority contract SO 2011-017.
Keywords: groundwater, natural tracer, FLOWPC, mean residence time, tunnel
discharges. |
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