Environmental Engineering Reference
In-Depth Information
267 streamgages in medium and large river basins as
part of the original USGS National Stream Quality
Accounting Network (NASQAN) (USGS 2008c).
The 25th, 50th, and 75th SSC percentiles were
0.02, 0.07, and 0.19 g/L, respectively. In 1995, the
NASQAN network was redesigned to focus on the
nation's largest river basins - the Mississippi (includ-
ing the Missouri and Ohio), Columbia, and Colorado
Rivers, and the Rio Grande. Horowitz (USGS, per-
sonal communication 2008) calculated the 10th,
25th, 50th, 75th, and 90th SSC percentiles for the
41 NASQAN streamgages in these large river basins
for the period 1994-2006 as 0.01, 0.03, 0.12, 0.32,
and 0.74 g/L, respectively.
Many streams transport near-zero SSCs at various
times. At the other extreme, SSCs measured during
surface runoff from 1989 to 1991 in the Little
Colorado River Basin, Arizona and New Mexico,
USA, commonly exceeded 100 g/L (Graf
et al
. 1996).
SSC values at the Paria River at Lees Ferry stream-
gage, Arizona, USA, exceeding 1000 g/L have been
reported (Beverage & Culbertson 1964).
In general, most of a river's annual sediment
budget is transported during infrequent high-fl ow
periods concomitant with relatively large SSCs. Any
proposed suspended-sediment surrogate technology
deployment should consider not only the statistics
quoted above, but also the potential maximum SSC
and, where appropriate, maximum particle sizes that
might be transported in the period of interest.
Table 1.1
Acceptance criteria for SSC data. The data are
considered acceptable when they meet these criteria 95% of
the time.
Suspended-sediment
concentration
Acceptable uncertainty
Minimum (g/L)
Maximum (g/L)
±
Percent
0
<
0.01
50
0.01
<
0.1
50-25 computed linearly
0.1
<
1.0
25-15 computed linearly
1.0
—
15
Adapted from Gray
et al.
(2002).
1.1.3 Ranges in US suspended-sediment
concentrations and suspended-sediment
discharges
Because of the spatial and temporal variability in
river sedimentological regimes, only generalities
regarding the expected range of SSCs and PSDs in
rivers can be made in the absence of site-specifi c data.
Rainwater (1962) produced an empirically derived
map of the 48 conterminous United States showing
mean SSC ranges for rivers, generalized over the
entire land area, for seven logarithmically based SSC
ranges. The SSC ranges were computed and deline-
ated as average annual discharge-weighted mean
SSCs, derived from annual measured SSL values
divided by their paired annual streamfl ow values at
streamgages. Computed SSC values in the largest
range exceeded about 48 g/L.
Meade & Parker (1985) simplifi ed the Rainwater
(1962) map into four SSC ranges: less than 0.3 g/L;
0.3-2 g/L; 2-6 g/L; and more than 6 g/L (Fig. 1.4).
They also produced a similar-type map for Alaska,
USA, using other information sources (Robert
Meade, personal communication 1985). These maps
(Fig. 1.4) also portray mean annual SSLs from
selected river basins to the coastal zone depicted by
half circles at river mouths. The area of each half
circle is proportional to the average annual sediment
mass discharged to the coastal zone. The maps can
serve as initial, general indicators of the suitability
of a selected sediment-surrogate technology in a river
reach of interest.
Additional information on the range of SSCs in US
rivers is available from Smith
et al.
(1987), who
computed percentile values for SSC data collected at
1.1.4 Information germane to suspended-
sediment-surrogate technology costs
After surrogate-technology effi cacy is resolved, cost
considerations are often of penultimate interest. The
cost of producing reliable, quality-assured suspended-
sediment data can be separated into four categories:
•
the purchase price of the instrument;
•
other capital costs associated with installation,
and initial operation of the instrument;
•
operational costs to maintain and calibrate the
instrument;
•
analytical costs to evaluate, reduce, compute,
review, store, and disseminate the derived data.
Of these four categories, only the purchase price
is straightforward to quantify. The others are
dependent on several factors, including site location
and physical characteristics, hydrological and
