Hydrological and suspended sediment regime in the Kolubara River during the extreme year of 2014

Abstract

The previous methodology of sampling and determining the suspended sediment con­cen­tration (SSC) in the rivers of Serbia is characterized by a number of disadvantages, so that any re­search of this kind has a large water management impact. In the largest number of hydrological stations in Serbia, daily SSC were obtained based on only one sampling, which raises the question of the representativeness of such sample. Previous SSC – water discharge relationship and detailed analyses of errors in calculating the suspended sediment transport on the profile of Draževac were done for the year of 2004, when the annual difference was very high, which required a very detailed ana­lysis and methodological improvements. In order to define the sediment regime in the Kolubara River, precise monitoring of SSC has been implemented since 2013. The Kolubara River has an unfavourable water regime which is reflected in the excessiveness of water runoff, with floods that are sudden, expressive and short-term, and long-term low waters, so, that are why it is cha­rac­terized by a large discharge and SSC variability. Incidentally, monitoring also covered the year of 2014, when the area of western Serbia (in particular the Kolubara River Basin) was under the influence of extreme climate events that strongly reflected on the hydrological condition with the absolute highest daily discharge. A total of 220 water samples were collected on Draževac gauging station in 2014, in order to determine SSC and sediment discharge. The total number of days covered was 206, which means that there were even more samplings per day, when the discharge was changing fast. The minimal daily measured SSC was only 0.0016 g/l and the maxi­mal recorded value of SSC was 2.6122 g/l and was measured in May at the water discharge of 1 260 m3/s. Тhe total amount of sus­pended sediment discharge at the profile of Draževac in 2014 was 1 104 435 t (the spe­ci­fic suspended sediment yield – 308 t/sqkm/yr). The main objective of this study is to improve SSC – water discharge relationship in the Kolubara River based on the extreme hydrological conditions in 2014.