Correlation Between Entrance Velocities, Increase in Local Hydraulic Resistances and Redox Potential of Alluvial Groundwater Sources - page 4

The Danube River

Kovin-Dubovac Drainage System

The area between Kovin and Dubovac occupies the southern part of the Banat Depression and comprises the alluvial plain of the Danube between these two towns, Fig. 12. Following construction of the Iron Gate 1 Hydroelectric Power Plant downstream from this area and the impoundment of the Danube in 1972, the groundwater levels in the riparian lands were permanently increased. This necessitated a protection system, which is comprised of dikes, drainage ditches, and a line of drainage wells. The role of the protection system is to maintain groundwater levels at pre-defined depths and prevent spreading of the Iron Gate 1 HPP reservoir impact further inland.

The lower part of the aquifer is made up of upper Quaternary/upper Pleistocene and Holocene gravels and sandy gravels, whose grain sizes vary to a large extent. They are overlain by medium-size gravels, sandy gravels and gravelly sands.

 

This sequence of sediments ends with semi-permeable silty sands, silts, and silty and riverine/bog clays. The average thickness of the aquifer strata is about 20 m, Fig. 13.

The size of d50 gravel sediment grains is generally from 0.5 to 20 mm, Fig. 14. The overlying sediments have a d50 grain size between 0.08 and 0.3 mm, and the semi-permeable aquifer roof sediments have a d50 grain size of 0.007 to 0.02 mm.

Water quality data were collected from 2010 to 2013. Table 2 shows these data on select wells of the drainage system shown in Fig. 12.

The average values of Eh were found to generally be in the range from 50 to 150 mV. Only a small number of samples measured more than 200 mV, Fig. 15. The low entrance velocities are a result of the fact that the wells are self-discharging.

 

fig12
Figure 12: Series of drainage wells along the left bank of the Danube between the towns of Kovin and Dubovac.

 

fig13
Figure 13: Typical section through the alluvial sediments between Kovin and Dubovac.

 

fig14
Figure 14: Grain-size distribution curves of the alluvial aquifer along the left bank of the Danube, between Kovin and Dubovac.

 

fig15
Figure 15: Average values of selected parameters of Kovin-Dubovac 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, Fe2+ – bivalent iron concentration in water, SO4 – concentration in water, and Ec – water conductivity).

 

Tab02