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

Because of the numerous size analyses and wet-sieve
separations that were made of samples collected with the test
samplers, no size information is presented in this report in
tabular fonn. However, defined analysis data and assigned
percent-finer values for all samples are stored on magnetic
media in the SAMPDA T A file for each run (see table 3 for
complete data-file names). These data are available on re-
quest (see Availability of Data, inside back cover).

Water Discharge

The constant water discharge established for each run
was attained during an adjuslment period at the beginning of
each run by varying the heighl of Ihe weir at the end of the
flume and the opening of the sluice gate at the upper end of
the flume 10 achieve the desired flow depth and bedload-
transport rate. Sufficient time was allowed belween signifi-
cant adjustments for the bed slope to change and reach a
quasi-equilibrium stale. After desired transport and depth
states were established and the data-collection period was in
progress, the sluice gate and weir settings remained nomi-
nally fixed, except during startup at the beginning of each
day and shutdown at the end of each day. However, during
most runs, the sluice gate had to be adjusted slightly now
and then to compensate for changes in river elevation at the
intake structure, and during several runs, weir height had to
be adjusted to maintain a reasonably constanl flow depth and
bedload-transport rate.
The water-surface elevation at a point about 25 ft
upstream from the weir was continuously monitored by an
electronic water. stage recorder mounted over a stilling well
on the outside wall of the flume. The recorder's voltage
output, which is proportional to water-surface elevation,
was graphed continuously by a strip-chart recorder. Period-
ically during each run, oulput voltages were read directly
from the recorder and noted on the slrip-chart record to
provide adjustment factors for correcting the pen trace.
The relation belween stage (water-surface elevation)
and discharge was eSlablished Ihrough calibrations based on
measurements of the flow volume accumulated during peri-
ods of several minutes. Six sets of calibration data were
collected during the course of run sequences with the four
different bed materials. For each set, a series of discharges
was established by sequentially adjusting the sluice-gate
opening. For each discharge, voltages from the stage
recorder were read and recorded both manually and via a
strip-chart recorder while flow was accumulated to near the
top of one of two 15,000-ft3 tanks outside of the laboratory.
The mean flow rate for each gate setting was detennined
from the measured volume and time of accumulation.
Analysis of the sets of calibration data indicated that
discharge varied with stage, weir height, and thickness of
bed material in the flume. The dimensionless weir discharge
coefficient, Cd' is plotted in figure 21 against the ratio of the

head on the weir, h, to height of the weir crest above the
channel bottom, W, for each set of calibration data. The
discharge coefficient was computed from:

Q = 2/3 Cd b hV2i/z

(I)

where Q is discharge,
b is the channel width, and
g is the gravity constant.
Also shown in figure 21 are linear regression lines that
represent each set of calibration data. Although the slopes of
all lines are not precisely the same, they are sufficiently
close that a single slope of 0.1534 can be used to character.
ize all data sets. By averaging the intercept values of lines
having a slope of 0.1534 that pass through each point of a
data set, an overall intercept was established for each data
set. The average intercept values plotted against H b' the
height of the bed surface above the flume floor, are pre.
sented in figure 22. Values of Hb for both the calibrations
and the individual runs were detennined by deducting the
mean depth of flow from the difference between the mean
waler-surface elevation at station 20 (upstream from the
slot) and the elevation of the flume floor.
Differences belween discharges measured during the
calibrations and counterpart discharges computed using the
relations depicted in figures 21 and 22 average 0.06 percent
and have a standard deviation of 0.81 percent. Mean water
discharges for each run listed in table 5 are believed to be
within about 2 percent of the true mean discharge.

Water-Surface Slope

Water. surface elevations were measured by using
manometers. A series of nine piezometer tubes that con-
nected to a common manometer board extended upstream
from the bedload trap (station 0) and tenninated in screened
outlets that were cemented along the centerline of the hori-
zontal flume floor every 20 ft from station 20 to station 180.
Bed material covered the outlets. All manometers were read
simultaneously at intervals throughout each run. The num-
ber of sets of readings thai were used to compute the average
water-surface slope for each run is listed in column 3 of
table 7. Many, but not all, of the sets of readings were
obtained concurrently with longitudinal streambed-surface
elevation profiles to facilitate computations of total depth.
Because of (I) the relatively deep depths and high
flow velocities attendant in many of the runs, (2) the pres-
ence of vertical struts at the slot (station 0), and (3) flow
expansion due to the absence of bed material downstream
from the slot, water-surface slopes were not unifonn
throughout the length of the flume. To exclude data obtained
from parts of the channel where slopes were not uniform,
water-surface elevations were subjected to statistical analy-
sis. For each run, every set of water-surface elevations was
used to detennine the water-surface slope for a base reach

20 Laboratory Data on Coarse-Sediment Transport for Bedload-Sampler Calibrations