Technological advances in suspended‐sediment surrogate monitoring

Abstract

[1] Surrogate technologies to continuously monitor suspended sediment show promise toward supplanting traditional data collection methods requiring routine collection and analysis of water samples. Commercially available instruments operating on bulk optic (turbidity), laser optic, pressure difference, and acoustic backscatter principles are evaluated based on cost, reliability, robustness, accuracy, sample volume, susceptibility to biological fouling, and suitable range of mass concentration and particle size distribution. In situ turbidimeters are widely used. They provide reliable data where the point measurements can be reliably correlated to the river's mean cross section concentration value, effects of biological fouling can be minimized, and concentrations remain below the sensor's upper measurement limit. In situ laser diffraction instruments have similar limitations and can cost 6 times the approximate $5000 purchase price of a turbidimeter. However, laser diffraction instruments provide volumetric-concentration data in 32 size classes. Pressure differential instruments measure mass density in a water column, thus integrating substantially more streamflow than a point measurement. They are designed for monitoring medium-to-large concentrations, are generally unaffected by biological fouling, and cost about the same as a turbidimeter. However, their performance has been marginal in field applications. Acoustic Doppler profilers use acoustic backscatter to measure suspended sediment concentrations in orders of magnitude more streamflow than do instruments that rely on point measurements. The technology is relatively robust and generally immune to effects of biological fouling. Cost of a single-frequency device is about double that of a turbidimeter. Multifrequency arrays also provide the potential to resolve concentrations by clay silt versus sand size fractions. Multifrequency hydroacoustics shows the most promise for revolutionizing collection of continuous suspended sediment data by instruments that require only periodic calibration for correlation to mean concentrations in river cross sections. Broad application of proven suspended sediment surrogate technologies has the potential to revolutionize fluvial sediment monitoring. Once applied, benefits could be enormous, providing for safer, more frequent and consistent, arguably more accurate, and ultimately less expensive sediment data for managing the world's sedimentary resources.

In situ characterisation of a concentrated colloidal titanium dioxide settling suspension and associated bed development: Application of an acoustic backscatter system

“…Diagnostic ultrasonic techniques however have proven to surmount such caveats to a practicable extent [1,30,31], enabling remote and relatively non-intrusive measurement with subsequently high resolution temporal and spatial profiles of suspended concentration, particle size and settling velocities [32]. Typical instrumentation include ex situ bench scale devices comprising separate transmitter and receiver probes [33][34][35], and even recent interest in B-scan ultrasound imaging [36].…”

Long-term continuous acoustical suspended-sediment measurements in rivers - Theory, application, bias, and error

“…As a result of the nonrandom variability in concentration about these curves, Glysson and others (2001), in an analysis of sediment data from 10 USGS gaging stations located in different regions of the United States, showed that the absolute value of the error in the annual sediment loads predicted by these curves fit to entire periods of record could equal 526 percent, and errors in the daily sediment loads predicted by sediment rating curves could be as high as 4,000 percent. Fortunately, the increasing availability of optical and acoustical sensors and associated advances in optical and acoustical theory have opened the possibility that these sensors may be used in conjunction with smaller numbers of conventional suspended-sediment samples to allow accurate sediment loads to be calculated (Gray and Gartner, 2009). Under conditions where suspended-sediment concentrations are not extremely high (that is, not >>1,000 mg/L), and concentration-independent changes in grain size or sediment color do not occur (for example, Conner and DeVisser, 1992;Sutherland and others, 2000;Voichick and Topping, 2014), measurements of optical-backscatterance (Schoellhamer, 2001;Schoellhamer and Wright, 2003) and turbidity (Rasmussen and others, 2009) have been shown to be highly correlated with conventional measurements of suspended-sediment concentration.…”

Estimating Suspended Sediment Concentration in Streams by Diffuse Light Attenuation

“…Another potential advantage of LASS is related to its relatively large sampling volume. The small measuring volume of turbidity probes and optical backscatter sensors enables these sensors to provide at-a-point surrogate measurement to TSS, which may not be representative of the mean cross-sectional TSS (Gray and Gartner 2009). The larger measuring volume of LASS provides a potential alternative and a more representative measurement for estimating suspended sediment flux.…”