Ambient Suspended Sediment Concentration and Turbidity Levels

The temporal variation of suspended sediment concentration and turbidity is an important component of the riverine environment. The maximum rate of discrete volumetric sample collection for laboratory determination of sediment concentration is one sample per minute for our field data collection on the effects of navigation on the Upper Mississippi River System. In an effort to obtain truly continuous measurements, another set of intakes and pumps were used to obtain and record continuous turbidity data while discrete samples were being collected. Ambient suspended sediment concentration samples and turbidity values were collected continuously for a three-hour period to measure variability over time. A turbidity-concentration correlation was also developed and used to estimate sediment concentrations for a point at which only turbidity was measured. Exponential decay curves were fitted to each of the three data sets. A regression equation between the turbidity and sediment concentration at one level was used to generate estimated sediment concentrations from the turbidity values at another level. Graphical and statistical characteristics of the continuous ambient data are presented and compared with the more common ambient measurements taken every few hours during a day of field data collection. This unique data set from the Illinois River illustrates the range of suspended sediment concentrations over a several hour period during steady flow conditions.