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

,SLUICE GATE
rSEDIMENT-
VERT1CAL
ENTRANCE
TUNNEL
" ~ 8 feet "'-y DIFFUSER
BAFF oJ

RETURN PIPE

LES

I.

213 feet

Figure 1. Schemalic diagram of bedload-sampler calibralion facilily.

weir and out of the laboratory into large volumetric tanks
that drain to the river. Whenever the weight of accumulated
sediment in a weigh pan exceeded the preset level, the
bottom doors opened and dumped the material onto the
auger. The auger transported the material out of the hopper
into the sediment-return sump. Clear water from the
constant-level tank mixed with the sediment in the sump to
produce a slurry that was pumped back to the upper end of
the flume and discharged on either side of the centerline of
the channel through the submerged Y diffusor. The water-
surface elevation in the constant-level water tank was main-
tained equal to the water.surface elevation in the channel to
minimize flow circulation vertically through the slot.

Control and Data-Acquisition Systems

A system of relays actuated by the voltage output
from the load cells controlled automatic dumping of the
weigh pans. The electrical apparatus and override switches
for this function, as well as an electronic time base for
continuously documenting time to the nearest second and
graphic and electronic data.acquisition instruments for
recording the voltage outputs from the weigh-pan load cells,
time, and several other variables, were housed in a movable,
air-conditioned console (fig. 5). To facilitate determination
of transport rates, output voltages from all load cells were
graphed continuously on strip-chart recorders and were
recorded digitally every 6 seconds on magnetic tape. The
strip-chart records allowed the continual filling and dump.
ing of the weigh pans to be monitored, whereas the digital
data served as the primary record for transport.rate determi-
nations.

TESTED BEDLOAD SAMPLERS

The Helley-Smith bedload sampler consists of an in-
take nozzle constructed of 1/4-in. steel or brass plate, a
mesh sample bag that is attached at the rear of the nozzle,

ADJUSTABLE WEIR

FlOW--

.1

..+

59 feet

and a supporting tubular-frame and tail assembly. The
standard (original) nozzle consists of a straight, square en-
trance section, several inches long, welded to a tapered
expansion section. The standard sample bag is 0.25-mm
mesh constructed in the general shape of an elongated pyra-
mid or cone. One standard nozzle has a 3- by 3.in. entrance
(fig. 6A), and another has a 6- by 6-in. entrance (fig. 6B).
Both standard nozzles have an area ratio, which is the ratio
of the exit area to the entrance area, of 3.22. This degree of
expansion gives the nozzles a hydraulic efficiency of about
1.54 (Druffel and others, 1976). Four modified nozzles, in
addition to the standard nozzles, were fitted with standard
sample bags and mounted into standard frames for testing.
Two of the modified nozzles had 3. by 3-in. entrances, and
two had 12- by 6-in. entrances (fig. 7). The expansion
sections of all four modified nozzles flared very little com.
pared to the standard nozzles; one nozzle of each size had an
area ratio of 1.10, and the others had an area ratio of 1.40.
In addition, a sampler having a standard 3- by 3.in. nozzle
and frame, but a 0.5-mm mesh sample bag, was tested in
one run; during the same run, a standard 3. by 3-in. sampler
was used in an untethered condition.
A standard Amhem sampler (fig. 8A) and a half.size,
modified VUV sampler were provided by The Department
of Minerals and Water Resources, Commonwealth of
Canada, for testing. Both of these samplers were supported
within a standard Arnhem frame. The unique feature of the
frame (fig. SA), which is used routinely with these samplers
in the field, is a laterally mounted leaf spring that is intended
to press the entrance nozzle of the sampler firmly onto the
bed. Although the frame worked marginally satisfactorily
with the Arnhem sampler, it apparently did not press the
entrance of the VUV sampler against the bed. As a result,
a disproportionate number of samples contained no material
whatever. Because of the questionable validity of many
samples collected with the half-size VUV, all samples were
rejected and deemed unrepresentative. The other tested
VUV sampler (fig. 8B) was a full-scale replica of Novak's
(1957) original sampler, except that the tail section was not
attached.

Bedload-Sampler Calibration Facility 3