Assessment of Riverbed Clogging in Reservoirs by Analysis of Periodic Oscillation of Reservoir Level and Groundwater Level

Eva Koren, Miran Veselič and Goran Vižintin
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Eva Koren: Department of Geotechnology, Mining and Environment, Faculty of Natural Sciences and Engineering, University of Ljubljana, Aškerčev 12, 1000 Ljubljana, Slovenia
Miran Veselič: Graduate School, University of Nova Gorica, Vipavska 13, 5000 Nova Gorica, Slovenia
Goran Vižintin: Department of Geotechnology, Mining and Environment, Faculty of Natural Sciences and Engineering, University of Ljubljana, Aškerčev 12, 1000 Ljubljana, Slovenia

Energies, 2021, vol. 14, issue 19, 1-15

Abstract: In the area of the the Krško alluvial field, the Brežice hydroelectric power plant (BHPP), with its surface water reservoir, was completed in 2017. The new BHPP reservoir dam is located approximately 7 km air distance downstream of the old Krško nuclear power plant (NEK) reservoir dam. The NEK dam was built in the 1970s. The primary purpose of the NEK reservoir is to provide fresh water for cooling the NEK nuclear reactor. To assess the impact of the newly built surface water reservoir on groundwater, we performed a series of data analyses prior to its construction. One part of the analysis relating to data from the monitoring facility of the NEK showed an interesting correspondence between the water level oscillation in the NEK reservoir and the groundwater oscillation in the nearby observation well. Based on measurements taken in 2000, we sought to estimate the clogging of the Sava riverbed sediments in the area of the old NEK surface water reservoir. To determine the permeability of the riverbed sediments, we applied geometry similar to that chosen by Hantush for his pumping test method. Using Fourier analysis, we determined the dominant frequencies from the hydrograph records of the NEK surface water reservoir and from the pressure probe in the nearby observation well. Based on the determination of the dominant frequency, we used the wave equation to compare the influence of different values of the hydraulic transmissivity of the clogged part of the NEK surface water reservoir on the transfer of its water oscillations to the groundwater in the observation well. For the hydraulic values of the non-clogged part of the aquifer (T, S), we assumed the values from the pumping experiments performed in the alluvial aquifer of Krško polje. We also assumed that the aquifer is homogeneous and isotropic, as Hantush had assumed in his method for the determination of semipervious river beds. The results obtained indicated the potential for estimation of the thickness of the clogging layer which, by analogy from applied geophysics, can be called the apparent thickness. This meant that the thickness could be determined on the basis of the default conceptual model rather than on real measurements. The presented method shows the potential for using the analysis of periodic oscillations in river reservoir level and nearby piezometers, as a method of monitoring riverbed clogging, in cases where periodical oscillations in reservoir level occur and observation wells are near enough to detect the oscillations.

Keywords: riverbed clogging; alluvial aquifer recharge; time series; analytical modelling (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2021
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