Environmental Engineering Reference
In-Depth Information
(a)
(c)
(e)
(b)
(d)
(f)
Fig. 1.3
Examples of Federal Interagency Sedimentation Project suspended-sediment samplers. (a) A US DH-48 rigid-bottle
sampler; (b) a US DH-81 rigid-bottle sampler; (c) a US D-74 rigid-bottle sampler closed, and (d) open; (e) a US D-96 fl exible-bag
sampler closed, and (f) open.
A list of FISP suspended-sediment samplers and
selected attributes is provided by Davis (2005) and
Gray
et al.
(2008). Examples of FISP rigid-bottle-
and fl exible-bag-type samplers are shown in Fig. 1.3.
A depth-integrating sampler collects and accumu-
lates a velocity- or discharge-weighted sample as it
descends and ascends through the water column pro-
vided that an appropriate constant transit rate is not
exceeded in either transit direction, and the sample
container does not overfi ll. A point-integrating
sampler uses an electrically activated valve, enabling
the operator to sample points isokinetically either in
parts of, or throughout, the water column. Both
types of samplers integrate the water column from
the water surface to within about 0.1 meters (m) of
the bed.
When properly deployed in a single vertical (or, in
the case of the point-integrating sampler, at multiple
points in a vertical), FISP isokinetic samplers provide
representative samples for the parts of the stream
sampled. When deployed using either the equal-
discharge-increment (EDI) or equal-width-increment
(EWI) sampling method (Edwards & Glysson 1999;
Nolan
et al
. 2005), an isokinetic sampler integrates
a sample proportionally by velocity and area, result-
ing in a discharge-weighted sample that contains an
SSC and PSD representative of the suspended mate-
rial in transport throughout the cross section at the
time that of sample collection.
Although the aforementioned manual samplers
have considerable benefi ts - most notably the acqui-
sition of demonstrably reliable suspended-sediment
data from rivers - they have inherent drawbacks. For
example, total costs associated with the manual
deployment of isokinetic samplers and subsequent
sample analytical costs can be substantial or even
prohibitive with respect to available resources.
Several safety considerations must be addressed
any time a hydrographer works in, over, or near a
watercourse. The sparse temporal distribution of the
derivative data - often but a single observation per
day - requires that daily SSL computations be based
on estimated SSC values and (or) indexed to another
more plentiful if imperfect predictive data source
such as river discharge by a sediment-transport curve
(Glysson 1987; Gray
et al
. 2008).
1.1.2 Performance criteria for
concentrations and particle-size
distributions produced by suspended-
sediment-surrogate technologies
The reliability and effi cacy of data produced by a
sediment-surrogate technology are predicated on the
