Environmental Engineering Reference
In-Depth Information
(a)
(b)
(c)
(d)
(e)
(f)
Fig. 2.4
Pressure-difference bed-load samplers. (a) and (c) Hand-held US BLH-84; (b) Cable-suspended US BL-84; (d) hand-
deployed Helley-Smith; (e) hand-deployed Elwha; (f) hand-deployed Toutle River-2 (TR-2) without bag (although only one
cable-suspended sampler is shown, all of these bed-load samplers are also available in cable-suspension confi gurations).
Lower photograph courtesy of Kristin Bunte, Colorado State University, USA.
data. Bed-load sampler calibrations are complicated
by a fundamental dichotomy, to wit: an innate ina-
bility to quantify the bed-load transport rate that
would have occurred in a stream section in the
absence of a deployed bed-load sampler, unless the
bed-load sampler's effi ciency is known
a priori
.
Most calibration studies have been performed in
laboratory fl umes where bulk bed-load transport rates
can be controlled. Although fl ume bed-load transport-
rate measurements - often referred to as “ground
truth” measurements - can be quite accurate, they do
not represent natural river conditions well. Leopold
& Emmett (1997) observed that a river's ability to
adjust its cross section to a variety of fl ows is a char-
acteristic not shared by a fi xed-wall fl ume. Riverine
sediment transport is determined by the geological
and physical setting of the river and river basin; thus,
sediment is not a controllable variable. The variety of
conditions controlled in a laboratory experiment
cannot be established in a natural river.
