Monitoring of the Iron Gate Hydropower and Navigation System on the Danube River - page 9

Fig18
Fig. 18: Layout of soil salinity monitoring locations, 2006-2010

 

Fig19
Fig 19: The effects of soil salinity/alkalization on sector IX

 

Fig20
Fig. 20: Layout of the system for flood protection of riparian lands

 

(VI) Monitoring of soil salinity and effect of backwater on agriculture

This program was executed in several phases, only in the areas along the IG1 reservoir. The most important was its initial phase, between 1962 and 1969, when the natural soil conditions were inspected on 124 points. During the IG1 exploatation period, the number of monitoring locations gradually decreased from 69 (1970-1981) to 20 (2007-2012, being limited to 4 areas on the left bank of the Danube – Fig. 18). It revealed that the process of soil salinization is weaker than expected, by both area and intensity. The protection system enables the adequate use of agricultural land along the Danube and its tributaries, with some localy identified problems (Fig. 19). Nevertheless, the available data are considered insufficient, and further research is needed.

(VII) Monitoring of flood defenses

Flood protection structures along IG1 and IG2 reservoir existed before their impoundment. However, these were small and very vulnerable structures. To achieve reliable protection in the reservoir conditions, and arrive at a satisfactory degree of safety, reconstruction of existing levees and construction of new ones was necessary (Fig. 20). Several settlements had to be relocated to higher altitudes, while others were protected by embankments and flood protection walls.

Levees protect the riparian land from the design 100-year flood, with 1.2- 1.7 m additional freeboard. Special attention was devoted to protection from wave-induced erosion by revetments on the outer slope of levees. Also, filtration stability of the levees was carefully investigated, and achieved by adequate sizing of the body and ballast.

Design criteria for construction and reconstruction of flood protection structures are the subject of ongoing review, following the experience gained from major flood events. This a permanent process that will continue into the future.

Jaroslav Cerni Institute is responsible for determining and monitoring the current state of flood protection structures, identifying and summarizing certain problems affecting the degree of flood protection, defining flood protection criteria, and, finally, contributing to the successful implementation of necessary emergency and rehabilitation works, as well as works on the reconstruction of these structures.

Jaroslav Cerni Institute has an advisory role during and after major floods on the Danube. The newest example is the flood that occurred in spring 2006, when the return period of peak discharges on the Danube and the Tisa rivers was approximately 100 years. Flood defence along IG1 reservoir, which lasted for almost two months, was generally successful. All levees which were reconstructed during the past 30-40 years in compliance with technical criteria, were able to withstand long-lasting high water levels (Fig. 21). The most challenging situations existed in towns along the Danube River (Novi Sad, Belgrade, Smederevo, Veliko Gradište and Golubac), where flood protection structures have insufficient freeboard above the flood level, due to urban planning criteria. Temporary dikes made of sandbags had to be erected on the top of existing structures (Fig. 22).

Problems noted in the preceding period (especially during major flooding in the Spring 2006) were generally of a local nature and in most cases solved by corrective and recovery works, or reconstruction. Reconstruction of all weak points in the flood protection system along IG1 and IG2 reservoirs, which were identified during the 2006 flood, is almost finished.

However, certain problems related to poor maintenance and the additional high water level increases due to IG1 reservoir sedimentation, are still present and require priority treatment.

 

Fig21
Fig. 21: Levee protecting Pancevacki rit area during 2006 flood

 

Fig22
Fig. 22: Temporary dike protecting Veliko Gradište (km 1059.5)