Correlation Between Entrance Velocities, Increase in Local Hydraulic Resistances and Redox Potential of Alluvial Groundwater Sources - page 5

Knićanin-Čenta Drainage System

This drainage system is comprised of drainage ditches and self-discharging wells, built in the 1970's to protect riparian lands from elevated stages of the Danube, resulting from its impoundment for the purposes of the Iron Gate 1 HPP. It is located on the left bank of the Danube, near the mouth of the Tisa River, Fig. 16. The Town of Knićanin is protected by a series of pumped wells along the perimeter of the city towards the Tisa. Self-discharging wells are lined up towards the Danube. Their operation is based on stages that cause discharge into the drainage ditches, whose water levels are controlled by a pumping station. Water from the drainage system is pumped back into the Danube by a pumping station at Čenta.

The thickness of the alluvial aquifer is from 15 to 28 m. The grain sizes of the lower zone are coarser than those of the upper zone. The aquifer floor is comprised of virtually impermeable clays, while the roof is made up of silty and clayey semi-permeable sediments. The central part of the cross-section features occasional clay and silty semi-permeable lenses, Fig.17.

Medium-grain sands are dominant in the central and upper parts of the aquifer, while the lower part features sandy and fine-grain gravels, Fig. 18.

In general, the average values of Eh of the studied wells did not exceed 250 mV, Fig. 19; only one sample measured 273 mV, Table 3. Two wells at Knićanin exhibited elevated entrance velocities, as a result of pumping. The wells along the Danube and the Begej are self-discharging.

 

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Figure 16:  Reach of the Danube between Knićanin and Čenta.

 

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Figure 17: Section through alluvial sediments along the left bank of the Danube between Knićanin and Čenta.

 

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Figure 18: Grain-size distribution curves of aquifer sediments between Knićanin and Čenta.

 

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Figure 19: Average values of selected parameters Knićanin-Čenta wells, by redox potential segment. (Legend: Eh – redox potential, d50 – aquifer grain size (50% of the grain-size distribution curve),
v – entrance velocity, O2 – oxygen concentration in water, NO3 – concentration in water, as N, Fe2+ – bivalent iron concentration in water, SO4 – concentration in water, and Ec – water conductivity.

 

Tab03

 

Veliko Gradište Drainage System

The Veliko Gradište Drainage System is located within the Town of Veliko Gradište, along a road adjacent to a regulated riverbank, Fig. 20. The wells are equipped with pumps, which maintain pre-defined groundwater levels in the riparian lands. Only two wells have been sampled in a single campaign. The data were certainly insufficient, but were still used in the present research.

The aquifer is comprised of coarse-grain sand and gravel, Fig. 21: d50 from 1 to 11 mm, and d10 from 0.1 to 0.3 mm.

The single groundwater sampling campaign involving two wells revealed a relatively high redox potential, Eh, of some 320 mV. However, it needs to be corroborated by further analyses.

 

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Figure 20:  Map of the Veliko Gradište site.

 

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Figure 21: Schematic section through the Veliko Gradište Drainage System.