Environmental Engineering Reference
In-Depth Information
cases, PSDs) in a variety of river types, fl ow condi-
tions, and sedimentological regimes. In some cases,
the computed SSC values and perhaps other data
types may be qualifi ed with estimates of uncertainty
(USGS 2005).
These are revolutionary concepts in the discipline
of sedimentology when considered from an opera-
tional perspective. The benefi ts of such applied capa-
bility could be enormous, providing for safer, more
frequent and consistent, arguably more accurate, and
ultimately less expensive fl uvial-data collection for
use in managing the world's sedimentary resources.
This chapter describes fi ve suspended-sediment-
surrogate technologies evaluated in fi eld or labora-
tory settings by the USGS for monitoring fl uvial
sediment with varying degrees of potential toward
providing continuous, largely automated time-series
data used for computing SSLs in rivers. All fi ve of
the
in situ
technological applications provide con-
tinuous SSC data, and at least two of those may
provide PSD data.
The chapter starts with an overview of traditional
instruments and techniques for suspended-sediment
sampling, against which the surrogate technologies
are evaluated. Descriptions of the theory, applica-
tions, some advantages, limitations, and costs of
each surrogate technology are presented and com-
pared. A subjective evaluation of the effi cacy of each
technology concludes this chapter. Use of fi rm,
brand, or trade names are for identifi cation purposes
only and do not constitute endorsement by the US
Government.
1.1.1 Background: traditional suspended-
sediment-sampling techniques
Suspended sediment is that part of the total-sediment
load (Fig. 1.1) carried in suspension by the turbulent
components of the fl uid or by Brownian movement
(ASTM International 1998). Instruments and
methods for collecting suspended-sediment data in
the USA have evolved considerably since 1838 when
the US Army Corps of Engineers' Captain Andrew
Talcott fi rst sampled the Mississippi River (Federal
Interagency Sedimentation Project 1940). The earli-
est suspended-sediment samples were collected by
use of instantaneous samplers such as an open con-
tainer or pail. By 1939, at least nine different types
of sediment sampler were being used by US agencies.
Most of the samplers had been developed by inde-
pendent investigators, lacked calibrations, and were
deployed using a variety of methods. A 1930s survey
of sediment-sampling equipment used in the US indi-
cated that the 30 instantaneous samplers studied had
limited usefulness either because of poor intake-
velocity characteristics or because of the short fi la-
ment of water-sediment mixture sampled (Federal
Interagency Sedimentation Project 1940; Nelson &
Benedict 1950; Glysson 1989).
In 1939, six US Federal agencies and the Iowa
Institute of Hydraulic Research organized a com-
mittee to consider the development of sediment
samplers, sampling techniques, and laboratory
procedures, and to coordinate such work among
the Federal agencies “actively concerned with the
Total sediment load
By origin
By transport
By sampling method
Suspended load
Suspended load
Wash load
Unsampled load
1
Bed-material load
Bed load
Bed load
1
That part of the sediment load that is not collected by the depth-integrating
suspended-sediment and pressure-difference bedload samplers used, depending
on the type and size of the sampler(s). Unsampled-load sediment can occur in one
or more of the following categories: (a) sediment that passes under the nozzle of
the suspended-sediment sampler when the sampler is touching the streambed
and no bedload sampler is used; (b) sediment small enough to pass through the
bedload sampler's mesh bag; (c) sediment in transport above the bedload
sampler that is too large to be sampled reliably by the suspended-sediment
sampler; and (d) material too large to enter the bedload-sampler nozzle.
Fig. 1.1
Components of total-sediment
load considered by origin, by transport,
and by sampling method.
From Diplas
et al.
(2008).
