The Effect of Hydrological and Anthropogenic Factors on the Chemical Properties of Water in the Canal Network of Southeastern Srem - page 04

 Fig04
Figure 4: Locations of monitoring points at which water was sampled for physical and chemical analyses.

 

Samples were collected from 11 July2008 to 17 November 2010. There were a total of 19 sampling campaigns.

The following chemical properties of the canal water samples were determined: pH, electrical conductivity – ECw, and carbonate, bicarbonate, chloride, calcium, magnesium and sodium concentrations. Standard analytical methods (APHA AWWA WEF, 1992) were applied.

Apart from the previously mentioned monitoring points (5 and 6), conductivity was measured along the Petrac Canal. Going upstream, the relevant points on the Petrac Canal were 5, 4, 7 and 8 (Fig. 4).

In order to compare the canal water quality data, information about the water quality of the Sava River was required. It was taken from the hydrological almanacs of the National Hydrometeorological Service.

The results of the hydrological assessment, as well as the water quality analyses, were represented and spatially analyzed using ESRI ArcGIS 9.1 software.

 

Results and Discussion

Hydrological Characteristics

In addition to the stages of the Sava River, the water levels of the drainage canals were found to be greatly affected by precipitation and evapotranspiration rates. The 40-year (1971-2010) average amount of precipitation at the rain-gauging station at Surčin is 654 mm. During the study period (2008, 2009 and 2010), the annual precipitation totals were 521 mm, 643 mm and 780 mm, respectively, meaning that the research was conducted in one dry year (2008), one average year (2009), and one wet year (2010). The water demand of the reference crop (ETo) was 1051 mm (2008), 1046 mm (2009) and 973 mm (2010).

The difference between ETo and rainfall (Fig. 5) was the largest during the summer months (July and August). A water deficit in the summer was registered even in the wet year 2010 (Fig. 5), attesting to the complexity of plant production under such climate conditions, as there is the need for crop irrigation even in years with high annual precipitation totals.

With regard to the effect of precipitation on the water levels of the Galovica Canal(2008-2010), it was apparent (Fig. 6) that mean monthly water levels at the Galovica PS did not depend on monthly precipitation totals. No correlation could be shown between these two parameters because the canal water levels were predominantly affected by the operation of the pumping stations. As such, the canal water levels in the wet year 2010 were below average because of the intensified operation of the pumping stations. On the other hand, the water levels during the average year 2009 were largely above average because the pumping stations were operated less frequently.

The volume of water available in the drainage system and the practicability of using water from the Sava River for irrigation are very important aspects of any assessment of the feasibility of irrigation relying on the drainage network. The water level of the drainage network was taken as the key indicator of the available water volume. Given that water levels at the Galovica PS are gauged on a daily basis,both upstream (Galovica Canal) and downstream from the weir (Sava River), it was possible to produce suitable water level plots. During the study period, the water levels of the Galovica Canal varied from 70.16 m above sea level to 71.60 m a.s.l. (Fig. 7). The altitudinal difference between the minimum and maximum water levels was about 1.5 m. The stage fluctuations of the Sava River were much larger and varied from 70.00 m a.s.l. to 75.10 m a.s.l.

Water levels of the Galovica Canal were lower 80% of the time than the stages of the Sava River (i.e. the stages upstream from the pumping station, Fig. 8). During such periods, excess water can only be evacuated from the canal network by pumping. In the remaining 20% of the time, the Sava's stages were lower than the water levels of the canal network, such that excess water could be removed to the river gravitationally. The stages of the Sava that allow gravitational evacuation are those below 71.18 m a.s.l. The duration curves in Fig. 8 show the water levels at the time of water sampling.

Figure 8 indicates that water was sampled over a broad range of river stages and water levels of the drainage system in southeastern Srem.

 

Fig5
Figure 5: Precipitation and reference evapotranspiration variation from June 2008 to November 2010.

Fig6
Figure 6: Average monthly water levels of the Galovica Canal and monthly precipitation totals.

Fig7
Figure 7: Water level plots of the Galovica Canal and the Sava River.

Fig8
Figure 8: Water level duration curves of the Sava River and Galovica Canal.