Environmental Engineering Reference
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7.5
Upper Whisker
75 percentile
Median
25th percentile
Lower Whisker
Probable outlier
Extreme value
6.0
4.5
3.0
1.5
0
0
9
18
27
37 46
Station cross section (m)
55
64
73
82
Fig. 2.3 Spatially averaged transport rates computed from 390 bed-load samples collected by a Helley-Smith bedload sampler and
a BL-86-3 bedload sampler (the latter identical to the US BL-84 bed-load sampler), at the USGS streamgage on the Colorado River
above National Canyon near Supai, Arizona, USA, October 1989.
From Gray et al. (1991).
of pressure-difference sampler from points across the
channel, a pattern in bed-load transport became evid-
ent with most bed load occurring in the center third of
the river (Fig. 2.3). These data are illustrative of the
fact that bed-load data collected by traditional manual
techniques as part of periodic or runoff-initiated site
visits are rarely suffi cient to reliably characterize the
spatiotemporal variability in bed-load transport rates
over periods exceeding a fraction of a day.
Lacking a reliable means for developing a bed-load
transport time series, practitioners often revert to
estimations based on stochastic techniques, such as a
bed-load transport equation or an empirically derived
bed-load transport curve with instantaneous water
discharge as the independent variable (Glysson 1987;
Gray and Simões 2008). However, the uncertainty
associated with bed-load-discharge estimates is rarely
quantifi ed or quantifi able, and is more often the
subject of speculation rather than reliable calculation.
Thus, considerable interest and effort has been
directed toward surrogate measurements that may
potentially provide a bed-load time series that is rep-
resentative of the cross section or reach of interest.
Sediment-surrogate technologies are defi ned as
instruments coupled with operational and analytical
methodologies that enable acquisition of temporally
and (or) spatially dense fl uvial-sediment data sets
without the need for routine collection and analysis
of physical samples other than for periodic calibra-
tion purposes. Bed-load surrogate technologies have
been addressed as part of at least three workshops
held since 2002, namely:
Erosion and Sediment Transport Measurements in
Rivers: Technological and Methodological Advances,
June 19-21 2002, Oslo, Norway, convened by the
International Commission of Continental Erosion of
the International Association for Hydrological
Sciences, and sponsored by the Norwegian Water
Resources and Energy Directorate (Bogen et al.
2003).
Federal Interagency Sediment Monitoring
Instrument and Analysis Research Workshop,
September 9-11 2003, Flagstaff, Arizona, USA,
sponsored by the Advisory Committee on Water
Information's Subcommittee on Sedimentation (Gray
2005).
International Bedload Surrogate Monitoring
Workshop, April 11-14 2007, Minneapolis,
Minnesota, USA, sponsored by the Advisory
Committee on Water Information's Subcommittee
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