Environmental Engineering Reference
In-Depth Information
1
Surrogate technologies for monitoring
suspended-sediment transport in rivers
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
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 fi eld 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 effi cacy 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-specifi c 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 fi rst 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 fi xed-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-
fi ler in fi xed-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-
tifi ably reliable sediment-surrogate technologies sup-
ported by operational and analytical protocols are
revolutionary concepts in fl uvial sedimentology. The
benefi ts could be enormous, providing for safer,
more frequent and consistent, arguably more accu-
rate, and ultimately less expensive fl uvial-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
