River Sediment Transport in Serbia - page 02

In order to come up with realistic and representative annual rates of suspended-sediment discharge by the Velika Morava, the hydrological and sediment transport parameters during the period from 1960 to 2003 needed to be assessed in parallel. This comparative analysis led to the following conclusions:

  • The values of Ps > 5 million tons tend to occur only in extreme situations (years with one or more major flood events).
  • The values of Ps < 2 million tons tend to occur in very dry years.
  • Based on the above, the level of annual sediment discharge of the Velika Morava is in the range from 2 to 5 million tons. In average hydrological conditions, the representative rate is Ps = 4 million tons/year.

The Velika Morava is a rare river in Serbia where bed-load has been assessed. The bed-load transport assessment was based on monitoring data and hydraulic analysis of the sediment transport capacity of the river. The assessment included the determination of all bed-load transport parameters, encompassing hydrological, hydraulic, morphological and sediment transport aspects. Bed-load monitoring has been conducted under low to medium-high flow conditions. Unfortunately, only one measurement was made under high flow conditions and that fact was a data interpretation constraint. Based on available data, the correlation between sediment transport and river discharge Gv(Q) was determined for two localities: the first is beyond the zone of influence of the Danube impoundment (at Ljubičevski Most), and the second in the zone of the mouth of the Velika Morava (Fig. 3).

Figure 4 shows bed-load transport duration curves for these two localities, based on the adopted function Gv(Q) and the water discharge duration curve at the gauging station of Ljubičevski Most.

 

Integration of the bed-load transport duration curves resulted in the following annual rates of bed-load transport:

  • Ljubičevski Most 210,000 tons/year
  • River mouth 19,000 tons/year.

The conclusion was that 210,000 tons/per year was a realistic indication of the annual rate of bed-load transport upstream from Ljubičevski Most. On the other hand, due to the effect of the impoundment, only 10% of the Velika Morava bed-load was deemed capable of reaching the river mouth to the Danube.

 

Lim River

The Lim River is a tributary of the Drina, coming into Serbia from Montenegro. Suspended sediment in the Lim was measured between 1963 and 2002 at Prijepolje Station, where the upstream catchment area is 3160 km2. Due to its hydrological regime, the highest suspended sediment concentrations (С) were registered from February to April, and the lowest from September to November. The extreme daily values of sediment concentration were: minimum of the order of 10-3 g/l, and maximum 9.3 g/l.

Variations of river discharge and sediment concentration in 1986, which was characterized by high sediment loads, are presented on Figures 5 (entire year) and 6 (flood wave in February 1986, Cmax= 9.2 g/l).

Based on the available suspended-sediment database, taking into account the sediment transported by flood waves (one of which is depicted in Fig. 6), a correlation was established between the sediment concentration (C) and river discharge (Q). The values of C and Q were used to assess the magnitude of sediment transport (P = C x Q), given in Table 1.

The suspended sediment duration curve (Fig. 8) was determined from the function P(Q) and  the river discharge duration curve (Fig. 7).

 

Fig03
Figure 3: Sediment transport (Gv) as a function of the Velika Morava discharge (Q), at Ljubičevski Most and the river mouth.

 

Fig04
Figure 4: Bed-load transport duration curves, at Ljubičevski Most and the river mouth.

 

Tab01