3 Surrogate technologies for monitoring suspended-sediment transport in rivers Advances in technologies for suspended-sediment transport monitoring programs in rivers show varying degrees of promise toward supplanting tra- ditional data-collection methods based on routine collection of physical samples and subsequent labo- ratory analyses. Mostly commercially available tech- nologies operating on bulk-, laser-, and digital-optic, pressure-difference, and acoustic principles have been or are the foci of field or laboratory tests by the US Geological Survey (USGS) and other organiza- tions. Advantages and limitations associated with each suspended-sediment-surrogate technology, con- sidered with deployment-site sedimentological char- acteristics and monitoring objectives, can be factored into the design of program networks using the most appropriate technology. Examples of factors that can limit or enhance the efficacy of a surrogate technol- ogy include cost (purchase, installation, operation, and data analysis), reliability, robustness, accuracy, measurement volume, susceptibility to biological fouling, volumetric- versus mass-concentration determinations, and suitability to the range of in- stream mass concentrations and particle-size distri- butions (PSDs). All of the in situ technologies require periodic site-specific calibrations to infer the sedi- mentary characteristics representative of the entire channel cross section. In March 2009, the USGS endorsed bulk optics (turbidity) for use in operational suspended-sediment monitoring programs, the first sediment-surrogate technology to receive USGS endorsement. Other technologies are likewise being considered for USGS acceptance. Nevertheless, hydroacoustic technologies show the most promise for use in operational suspended- sediment monitoring programs. A fixed-mounted, self-contained single-frequency acoustic backscatter instrument supported by appropriate deployment, calibration, and data-analyses protocols presents the prospect for automated collection of continuous time-series suspended-sediment-concentration data in selected river reaches. The anticipated adaption of a multi-frequency acoustic Doppler current pro- filer in fixed-mounted mode portends the potential for even more accurate monitoring of suspended- sediment concentration (SSC) and transport, possi- bly by particle-size classes. Laser -optic instruments deployed in situ or manually that provide PSDs and concentrations also show considerable promise. Endorsement and broad-scale deployment of cer- tifiably reliable sediment-surrogate technologies sup- ported by operational and analytical protocols are revolutionary concepts in fluvial sedimentology. The benefits could be enormous, providing for safer, more frequent and consistent, arguably more accu- rate, and ultimately less expensive fluvial-sediment data collection for use in managing the world’s sedimentary resources. 1.1 Introduction Fluvial sediment and sorbed materials are the most widespread pollutants affecting US rivers and streams (US Environmental Protection Agency 2008). The need for reliable, comparable, cost-effective, spatially and temporally consistent data to quantify the clarity and sediment content of waters of the USA has never been greater. Yet resources dedicated to this need have been in decline for more than two decades. For instance, the number of sites at which the USGS 1 Sedimentology of Aqueous Systems, 1 st edition. Edited by Cristiano Poleto and Susanne Charlesworth. © 2010 Blackwell Publishing John R. Gray 1 & Jeffrey W. Gartner 1 (editors) Chauncey W. Anderson 1 , Gregory G. Fisk 1 , Jeffrey W. Gartner 1 , G. Douglas Glysson 1 , Daniel J. Gooding 1 , John R. Gray 1 , Nancy J. Hornewer 1 , Matthew C. Larsen 1 , Jamie P. Macy 1 , Patrick P. Rasmussen 1 , Scott A. Wright 1 & Andrew C. Ziegler 1 1 United States Geological Survey, USA COPYRIGHTED MATERIAL