Dynamics of suspended sediment in the Juzna Morava river, south-eastern Serbia

This study estimate the temporal trends of recent suspended sediment in Juzna Morava river. The variations of suspended sediment transport were analyzed at different time scales (inter-annual, monthly and seasonal, among different periods), based on 47-year hydrological data from the outlet hydrological station. The results indicate of a decline in suspended sediment concentration and sediment load in the long-time series, which can be divided into three periods: high SSC or Qs (1961-1976), medium SSC or Qs (1977-1988) and low SSC or Qs (1989-2007). The average annual SSC and Qs of these three periods are SSC=0.7284 g/l, SSC=0.3580 g/l, SSC=0.1865 g/l, and Qs=4260x103 t, Qs=2277 x103 t, Qs=789 x103 t, respectively. The decrease in SSC and Qs is at the significance level of ?=0.001. The frequency distribution of the daily SSC show that cumulatively 92% of daily SSC during the low stage was u distributed in classes up to 0.5 g/l, versus 82% during the medium and 67% during the high period. The frequency of daily SSC in the class of 1-5 g/l decreases over time, from 14% in high period to 6% in low period. In the period 1989-2007 have not been reported SSC greater than 5 g/l. Different patterns of suspended sediment concentration SSC-Q hysteretic loops have been observed for each period. Two types of hysteretic loops were found at Juzna Morava River: figure-eight typical of periods 1961-1976 and 1978-1988 and counter-clockwise in period 1989-2007. Human impact is the main factor in reducing suspended sediments. An important change in agriculture land in the basin recorded a significant impact on sediment transport.