FLOOD01191

• County: Statewide
• Title: Laboratory Data on Course-Sediment Transport for Bedload-Sampler Calibrations
• Date: 1/1/1987
• Prepared By: USGS
• Floodplain - Doc Type: Educational/Technical/Reference Information

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EXPLANATION

o DATA SET 1
. DATA SET 2
o DATA SET 3
. DATA SET 4
D. DATA SET 5
& DATA SET 6

//

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1.0

1.2

1.4

1.8

1.6

RATIO OF HEAD ON WEIR TO HEIGHT OF WEIR CREST
ABOVE FLUME FLOOR, h/W

Figure 21. Variation of discharge coefficient wilh ralio of the head on the weir to Ihe height of the weir cresl above the flume floor.
Each regression line represents a different set of calibration data.

between stations 20 and 40 (upstream from the slot). Slopes
for the base reach then were compared statistically, at con.
fidence coefficients of 90 and 95 percent, with counterpart
slopes for reaches adjacent to the base reach to ascertain
whether or not the slopes of the adjacent reach were likely
to be from the same slope population as those for the base
reach. If so, elevations from the adjacent reach were in-
cluded with elevations from the base reach to form a new
base reach, and slopes for the new, longer base reach were
redetermined by linear regression. These slopes, in turn,
were compared with slopes from the next adjacent reach to
establish if all slopes were part of the same population. This
process of extending the length of the base reach was contin-
ued until it was evident that the slopes for Ihe adjacent and
base reaches were different. The average slope for the run
was then taken as the average of the least-squares slopes
from all sets of elevations for the base reach.
The analysis procedure is based on the premise that
changes in slope occur abruptly between the uniform and
nonuniform reaches, rather than gradually throughout the
entire reach. Although the premise cannot be verified be-

cause of the considerable variations in slopes, graphs of all
computed average slopes, which also were used in making
judgments about the commonality of slopes, indicate that
slope changes in the water surface usually were reasonably
abrupt.
The data in columns 4 and 5 of table 7 indicate, for
each run, the stationing of the end points of the reach for
which a uniform slope was presumed to exist; table 5 lists
the mean slope values for all runs. For those few runs in
which relatively long reaches of common slope were sepa-
rated by a short reach of dissimilar slopes, the average slope
was determined by using elevations from the entire reach.
The precise degree to which computed mean water-
surface slopes represent uniform-flow conditions cannot be
estimated reliably. However, on the basis of variances of the
slope sets used to define the mean slope for each run, most
mean slope values (see column 7 of table 5) can be expected
(99-percent confidence coefficient) to be well within 25
percent of the true mean slope, except for slopes for the
23.5-mm runs, which may be somewhat less accurate.

Hydraulic and Sedimentologic Data 21