Monitoring of the Iron Gate Hydropower and Navigation System on the Danube River - page 10

(VIII) Monitoring of water and sediment quality

Water quality deterioration was expected in the IG1 reservoir due to high water levels and low velocities reducing the stream's self-purification potential resulting in increased eutrophication effects. Also, it was anticipated that the sediment deposition would present a potential threat to the ecosystem, due to the accumulation of hazardous and harmful substances.

The research of the Jaroslav Cerni Institute has the aim to determine all processes in the system (water and sediment), to predict changes in water quality and to implement all necessary measures to prevent negative effects.

Regular monitoring started in 1985, when the basic program was settled with Romanian part in Bucharest (1985). Regular water quality monitoring within the common Serbian-Romanian sector of the Danube river (between the IG1 dam and km 1075) have been performed between 1985-1991. After a long pause (1992-2000), the investigation restarted in 2001 with regular programme and modified methodology, which includes hydrobiology and radiology analyses. Afterwards, the program was extended to the upper sector of the Danube, and its tributaries, upon the demand of the Serbian water management authority. Regular sampling and analyses of water and sediment parameters were previously performed 2 times per year at 8 sampling sites along a 230 km long reservoir reach (5 of them within the IG1 reservoir, as shown on Fig. 23). An additional 2 sampling campaigns were instituted in 2010, including sampling at 12 sites along 400 km of the IG1 and IG2 reservoirs, during low and high flows.

The anticipated forecast of the deterioration of water quality of IG1 reservoir has not been fulfilled. According to all physical and chemical parameters, the water quality corresponds to the specified class 2 according to Serbian classification. There are certain temporary exceptions indicating organic pollution, as well as an increase of Fe and suspended solids. The occasional occurrence of phenols and mineral oils is a consequence of waterborne traffic. Other dangerous matter was recorded within permissible limits for this class of water.

Water quality continuously improves along Serbian sector of the Danube river (Fig 24). The IG1 reservoir has an important role in this process, functioning as a large physical and biochemical reactor where intense decomposition of organic matter and removal of organic matter and nutrients from the system takes place.

According to the biological parameters (phytoplankton and zooplankton), the water quality corresponds to class II, while macroinvertebrate species indicate class III water quality. The IG1 reservoir has a very short retention time (up to 10 days). There is no temperature stratification and stable oxygen stratification, and there is a lack of an intensive eutrophication potential. The water quality is still satisfactory, due to the high capability of self-purification, although it varies as a consequence of the incoming load, hydrological conditions and water temperature. Up-to-date investigations of sediment quality revealed a significant content of organic and inorganic matter.

(IX) Monitoring of riverbank and landslide stability

Still and active landslides, and other riverbank instability phenomena, are present on the right bank of the Danube. There are 26 locations with recorded instabilities (12 along IG1 and 14 along IG2 resđÁrvoir).

After 2003, the Jaroslav Cerni Institute improved the previously implemented monitoring program and started geodetic surveys and geophysical investigations on some locations, where a higher instability risk was anticipated, endangering hydropower plants and reservoirs, but also infrastructure in the riverine areas.

The monitoring revealed that the reservoirs, in principle, had a favorable impact. Namely, the height and speed of water level fluctuations is reduced in reservoir conditions, and thus also the erosion of valley sides.

 

Conclusions

The implementation of the monitoring program provides information and data on the status of the reservoir and the riparian belt, as well as on the efficiency of protective structures. Such information and data lead to recommendations for any additional works and measures. Based on the results of monitoring and the required analyses, it is also assessed whether and under which conditions the operating mode of the Iron Gate HPNS may be altered.

All of the above demonstrates the need for continued monitoring of the Iron Gate HPNS impacts on the reservoir and the riparian land under the existing or a modified program.

 

Fig23
Fig. 23: Map of sites for water and sediment quality investigations

 

Fig24
Fig. 24: Measured values in a Box-plot diagram of BPK5 concentration in 2006-2011 series on boundary and chosen internal profiles of Danube river in the Republic of Serbia