Hysteresis in suspended sediment to turbidity relations due to changing particle size distributions

Abstract

[1] Turbidity (T) is the most ubiquitous of surrogate technologies used to estimate suspended-sediment concentration (SSC). The effects of sediment size on turbidity are well documented; however, effects from changes in particle size distributions (PSD) are rarely evaluated. Hysteresis in relations of SSC-to-turbidity (SSC$T) for single stormflow events was observed and quantified for a dataset of 195 concurrent measurements of SSC, turbidity, discharge, velocity, and volumetric PSD collected during five stormflows in 2009-2010 on Yellow River at Gees Mill Road in metropolitan Atlanta, Georgia. Regressions of SSC-normalized turbidity (T/SSC) on concurrently measured PSD percentiles show an inverse, exponential influence of particle size on turbidity that is not constant across the size range of the PSD. The majority of the influence of PSD on T/SSC is from particles of fine silt and smaller sizes (finer than 16 mm). This study shows that small changes in the often assumed stability of the PSD are significant to SSC$T relations. Changes of only 5 mm in the fine silt and smaller size fractions of suspended sediment PSD can produce hysteresis in the SSC$T rating that can increase error and produce bias. Observed SSC$T hysteresis may be an indicator of changes in sediment properties during stormflows and of potential changes in sediment sources. Trends in the PSD time series indicate that sediment transport is capacity limited for sand-sized sediment in the channel and supply limited for fine silt and smaller sediment from the hillslope.Citation: Landers, M. N., and T. W. Sturm (2013), Hysteresis in suspended sediment to turbidity relations due to changing particle size distributions, Water Resour. Res., 49, 5487-5500,

Continuous measurement of suspended sediment concentration: Technological advancement and future outlook

“…The dependence of turbidity readings on sediment size of sample has been studied extensively in laboratory set-ups [41,47]. Haimann et al [33] used turbidity to determine SSC, sediment transport and sediment load at Hainburg Road Bridge, Danube River.…”

Sampling strategies to estimate suspended sediment concentration for turbidimeter calibration

“…These samplings present high cost and low efficiency, since the amplitude of SSC is not satisfactory to construct a calibration curve, requiring extrapolation to samples with higher turbidity, increasing the chances of error. The costs of sampling rainfall events are high, but the information obtained has great reliability, with a good amplitude of SSC data and sediment characteristics (size, color, mineralogy) resulting in a reliable database (Bouchez et al, 2011;Landers & Sturm, 2013). Furthermore, according to Lewis (1996), few pairs of data (less than 10) representing the SSC interval should be sufficient to establish a reliable relationship between turbidity and SSC during these rainfall events.…”

Characterization of sediment transport upstream and downstream from Lake Emory on the Little Tennessee River near Franklin, North Carolina, 2014–15

“…Streamflow, in cubic feet per second Percentage of particles finer than 0.0625 milliliters According to Landers and Sturm (2013): "The SSC~Q relation typically exhibits leading, clockwise hysteresis which is often ascribed to resuspension of sediment from the stream channel at the initiation of storm runoff and to relatively limited sediment supply on the stormflow recession. "…”