Environmental Engineering Reference
In-Depth Information
2
Surrogate technologies for monitoring
bed-load transport in rivers
John R. Gray
1
& Jeffrey W. Gartner
1
(editors)
Jonathan S. Barton
2
, Janet Gaskin
3
, Smokey A. Pittman
4
&
Colin D. Rennie
3
1
United States Geological Survey, USA
2
National Aeronautics and Space Administration, USA
3
University of Ottawa, Canada
4
Graham Matthews and Associates, USA
Surrogate technologies for bed-load transport moni-
toring are being evaluated toward eventually sup-
planting traditional data-collection methods that
require routine collection of physical samples and
subsequent fi eld or laboratory analyses. Commercially
available and prototype technologies based on active-
and passive-hydroacoustic principles are the foci of
much of the current research on bed-load surrogate
techniques, and are the subjects of this chapter.
Field and laboratory tests of bed-load surrogate-
monitoring techniques using active hydroacoustics
(acoustic Doppler current profi lers (ADCPs)) in
sand- and gravel-bed rivers or passive hydroacoustics
(various sensors) in gravel-bed rivers have been
shown to provide useful data in a limited number of
fl ume and fi eld tests, and some are the subject of
continuing research. Research on other technologies
including tracer-tracking (visual, radioactive, mag-
netic, and radio); sonar, load-cell, videography,
particle-tracking, ground-penetrating radar, and
magnetic techniques is ongoing in several countries.
Similar to choices for monitoring suspended-sedi-
ment transport, selection of an appropriate technol-
ogy for bed-load transport monitoring usually entails
an analysis of the advantages and limitations associ-
ated with each technique, the monitoring objective,
and the physical and dynamic sedimentary charac-
teristics at each deployment site. Some factors that
may limit or enhance the effi cacy of a surrogate
technology used to monitor bed-load transport
include cost (purchase, installation, operation, cali-
bration, and data analysis), reliability, robustness,
accuracy, size and location of the instantaneous and
time-integrated measurement realm, and range in
size of bed-load particles. Most if not all surrogate
technologies for monitoring bed load, including
passive and active hydroacoustics, require periodic
site-specifi c calibrations to infer transport rates
occurring over the entire channel cross section.
Should bed-load surrogate technologies prove suc-
cessful in a wide range of applications, the monitor-
ing capability could be unprecedented, providing the
prospect of obtaining continuous records of bed-load
discharge potentially qualifi ed by estimates of uncer-
tainty. As with suspended-sediment surrogate tech-
nologies, the potential benefi ts could be enormous,
providing for more frequent and consistent, less
expensive, and arguably more accurate bed-load
data obtained with reduced personal risk for use in
managing the world's sedimentary resources.
2.1 Introduction
Bed load is the part of total-sediment load that is
transported by rolling, skipping, or sliding on the
riverbed (ASTM International 1998) (Fig. 2.1).
Historically, bed-load data for US rivers have been
produced by gradation and gravimetric analyses per-
formed on samples obtained with manually deployed
samplers (Edwards & Glysson 1999; Kuhnle 2008).
As with suspended sediment, traditional bed-load
data-collection methods tend to be expensive,
labor intensive, time-consuming, diffi cult, and under
some conditions, hazardous. Specialized instruments
and considerable training in their proper deployment
are prerequisites for obtaining reliable bed-load
samples.
