An inexpensive turbidimeter for monitoring suspended sediment

Abstract

Temporal and spatial variability of suspended sediment in proglacial streams means that discrete monitoring is unlikely to characterize suspended sediment patterns accurately. Continuously recording turbidimeters provide a solution to the temporal problem of sampling. However, the problem of spatially limited sampling is constrained largely by the cost of establishing networks of commercially available turbidimeters. In this paper we present the design and testing of an inexpensive, custom-built, datalogger-compatible and rugged infrared nephelometric turbidimeter (the “HOBS”). Laboratory testing showed that the HOBS was most sensitive to coarse clay and fine silt fractions, the dominant particle sizes transported in proglacial streams. Further testing showed that the HOBS had a non-linear but regular response to bulk sediment concentrations from 0 to ∼3500 mg L −1, with explained variances of 99.2% to 99.8%. In the field, the HOBS showed a linear response up to 2000 mg L −1 and a non-linear response up to 10,000 mg L −1 with explained variances between 75% and 83%. This variability emphasizes the necessity of individual, site specific field calibrations. The HOBS's sensitivity to a wide range of suspended sediment concentrations is particularly suited for use in proglacial streams where large fluctuations in concentration are likely. The generic design, low cost, and good performance of the HOBS suggests potential for application in other environments where distributed monitoring of suspended sediment is of interest.