Measuring Suspended Sediment

Calculation of in situ acoustic sediment attenuation using off‐the‐shelf horizontal ADCPs in low concentration settings

“…For example, Gray and Landers [, Figure 18; data in Landers and Sturm , ] computed α s,in situ for a truncated profile that gave an attenuation coefficient of 0.35 m 2 /kg and attenuation of 2.1 dB/m. This is an order of magnitude greater than the theoretical attenuation for the reported concentration of 694 mg/L in Gray and Landers [, Figure 18], a D 50 of 25 μm from a log normal GSD, a St. Dev.…”

“…of 1.0, and a1500 kHz ADCP (computed using equations (9) and (15)). The difference between a s,in situ and a s,theo is even greater if you use the 185 mg/L given in Gray and Landers [2014] and Landers [2011]; two SSC values are reported for the same site and date due to rapidly changing conditions. In the context of our results, it seems likely that their high value of a s,in situ reflects a profile truncated to select the steeper part of a concave profile or the presence of a cross-stream gradient in concentration.…”

Contributions of human activities to suspended sediment yield during storm events from a small, steep, tropical watershed

“…The Autosampler inlet tubing was oriented down-stream, just below the water level sensor, approximately 30 cm above the stream bed, on rebar positioned midstream. Samples were analyzed for SSC on-island using gravimetric methods (Gray, 2014;Gray et al, 2000). Water samples were vacuum filtered on preweighed 47 mm diameter, 0.7 lm Millipore AP40 glass fiber filters, oven dried at 100°C for one hour, cooled and weighed to determine SSC (mg/L).…”

Sediment acoustic index method for computing continuous suspended-sediment concentrations

“…Characterization of suspended sediment using acoustic backscatter in water has been described and developed for several decades (Urick, , 1975Thorne and others, 1991;Lynch and others, 1994;Holdaway and others, 1999;Topping and others, 2006;Wall and others, 2006;Simmons and others, 2010;Guerrero and others, 2011;Thorne and others, 2011;Landers, 2012;Clark and others, 2013;Gray and Landers, 2014;Medalie and others, 2014;Topping and others, 2015;Wood and others, 2015). A review of the theory and its development is provided in appendix 2 of this report.…”

“…Sediment acoustic index methods also can leverage the widespread use of acoustic Doppler velocity meters (ADVMs), which are commonly used for streamflow monitoring but also record acoustic backscatter data that can be related to sediment concentration. The opportunity to obtain continuous suspended-sediment data is being pursued by many scientists within and outside of the U.S. Geological Survey (USGS), following general principles that are well founded in theory and described in the literature (Topping and others, 2006;Landers, 2012;Gray and Landers, 2014;Topping and others, 2015;Wood and others, 2015). Standard protocols, however, are lacking, and best methods require detailed data computations that have not consistently been described and used (Landers and others, 2012).…”