A two-decade record of variations in suspended sediment in the Warta River, a lowland river in western Poland

Abstract

Fluctuations in suspended sediment concentration (SSC) has been investigated in the Warta River (western Poland), based on data obtained for the period 1961–1980 from three gauge stations located in upstream, middle-stream and downstream areas. Over the two decades, the SSC values demonstrated wide fluctuations and an overall increase at each gauge station. No significant correlation was generally observed between SSC and discharge but high SSC was found to follow low discharge and increasing temperature during the summer seasons in some years. Measurements of SSC and discharge were used to estimate total annual suspended sediment load (SSL). SSL values were found to increase downstream along with an increase in discharge. SSC decreases along the river course. However, when it comes to changes over time, SSL variability was mainly determined by SSC changes. The maximum SSC values were primarily caused by anthropogenic factors: the disposal of mine wastewater upstream, river training works, increased urbanisation and the intensification of sewage disposal. Where the river catchment has been greatly affected by anthropogenic factors, a denudation index calculated solely based on SSC and discharge does not appear to reflect the actual denudation rate, and must be treated with caution.

Suspended sediment in lowland rivers – towards identifying the ratios of mineral and organic components and their variation during the year

“…It is widely recognised that SSC correlates positively with discharge during isolated hydrological events, such as floods, resulting in a variety of hysteresis loops (Williams, 1989;Pagano et al, 2020). Previous studies on the River Warta, based on data taken between 1960 and 1980 (Skolasińska & Nowak, 2018;Skolasińska et al, 2020) did not find any clear relationship between discharge and suspension concentration. The findings also indicate that during flooding, when discharge increases, SSC decreases; however, in some years, high SSC was observed in summer periods with low discharge.…”

“…The movement of suspended load varies considerably over time (e.g., Jarocki, 1957;Olive & Rieger, 1992;Skolasińska et al, 2020). It shows an uneven distribution on vertical and horizontal cross-sections of the river channel and concentrations of both mineral and organic components tend to vary with depth in the water column, as demonstrated in Figure 1 (Shah-Fairbank & Julien, 2015).…”

“…This may be one of the reasons why the factors that influence sediment flux variation in rivers, and the relationships between them, remain relatively poorly understood and require further research (Vercruysse et al, 2017;Peng et al, 2020;Vercruysse et al, 2020). In addition, previous research on variations in suspended sediment transport has also been found to be inadequate, as noted by Skolasińska & Nowak (2018) and Skolasińska et al (2020).…”