Correlation Between Entrance Velocities, Increase in Local Hydraulic Resistances and Redox Potential of Alluvial Groundwater Sources - page 6

The Velika Morava River

Ključ Groundwater Source

The Ključ Groundwater Source provides water supply to the City of Požarevac. It is located along the Velika Morava River and comprises a portion of its alluvial plain, Fig. 22.

The aquifer is comprised of polycyclic riverine/lacustrine and alluvial sediments, whose total thickness is 15 to 20 m. The part of the aquifer from which groundwater is extracted is predominantly represented by sandy gravels. The thickness of these gravels in the Ključ area is from 6 to 11 m, and adjacent to the Velika Morava from od 8 to 12 m. The gravel sequence is locally overlain by sands, whose thickness is 2 to 6 m. The sandy sequence is covered by semi-permeable sediments, generally loess and clay, whose thickness ranges from 3 to 5 m. A typical lithological section through the sediments at the source is shown in Fig. 23, along with the line of the Velika Morava riverbed indicative of a good hydraulic contact between the groundwater and the river.

The above is corroborated by the grain-size distribution in the source area, Fig. 24. The aquifer roof and floor grains are up to a thousand times finer than the grains of the aquifer itself.

 

The groundwater at the Ključ Groundwater Source along the Velika Morava is characterized by a high redox potential, greater than 300 mV, along with a relatively high concentration of dissolved oxygen, Table 4, Fig. 25. There is virtually no bivalent iron, but nitrate concentrations were found to be elevated, suggesting pollution from the ground surface.

 

Comment on Oxic States

A summary presentation of the parameters of all the studied locations is shown in Fig. 26. The data were previously interpreted as representative by well, then the values averaged in the given Eh intervals (of 50 mV). The wells of the Belgrade Groundwater Source were dominant, where the prevailing redox potential was below 150 mV. There was a significant decrease in Fe2+ concentrations, and increase in d50 with increasing Eh.

Figure 27 shows the average values of the analyzed parameters for three most characteristic sites: Belgrade Groundwater Source (the Sava River), Kovin-Dubovac Drainage system (the Danube River), and Ključ Groundwater Source (the Velika Morava River).

 

fig22
Figure 22: Map of Ključ Groundwater Source.

 

fig23
Fig. 23:  Lithological section through the Ključ Groundwater Source.

 

fig24
Figure 24: Grain-size distribution of alluvial sediments in the Ključ Groundwater Source area.

 

fig25
Figure 25: Average values of selected parameters of the Ključ Groundwater Source near the City of Požarevac, 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.)

 

tab04

 

fig26
Figure 26: Average values of selected well parameters of all study areas, by redox potential segment. (Legend: Eh – redox potential, d50 – aquifer grain size (50% of the grain-size distribution curve), vprop  – recommended 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).

 

fig27
Figure 27: Comparison of average values of several parameters of the groundwater and medium: sites on the Sava River (Belgrade), the Danube River (Kovin-Dubovac, Knićanin-Čenta), and the Velika Morava River (Požarevac).