FLOOD03637

• County: Statewide
• Basin: Statewide
• Title: Incipient Motion and Sediment Transport
• Date: 10/1/1973
• Prepared By: Journal of the Hydraulics Division
• Floodplain - Doc Type: Educational/Technical/Reference Information

1696

OCTOBER 1973

HY10

-3,004, 24.930, -8.828, and -4.566, respectively. These T values indicate the
probability that log C, is not a function of log (V.lw) is less than 0.005 while
~he probabilities that log C, is not a function of any of the rest of the me~tioned
Independent variables are less than 0.00 I.
Eq. 26 is the general equation the writer would like to propose to engineers
for their consideration in predicting the total sediment concentration in both
~aborator~ f1um~s and natural rivers. The dimensionless critical velocity, Vc/w.
IS determined either by Eq. 18 or Eq. 19 depending on the value of the shear
velocity Reynolds number, U.djv. A comparison of the measured and predicted
(Eq. 26) total sediment concentration is shown in Col. 13 of Table 2 in terms
of logarithmic units. The weighted average standard error of estimate for all

16.

HY10

INCIPIENT MOTION

for a given value of unit stream power will be studied herein in accordance

with Eq. 26. d' d
Fig. 6 shows the effect of the variation of particle size on the pre Jcte.
total sediment concentration with T = 200 C and D = 0.2 ft (6.1 cm). ThiS
figure shows that the predicted total sediment concentration from Eq. 26 decreases
with increasing particle size for a given unit stream power, wat~r temperature,
and water depth. As shown in Fig. 7, Gilbert's (6) data confirms. the result
shown in Fig. 6. The slight scattering in Fig. 7 may be due mamly to the
variation of water temperature which Gilbert did not measure.

1O~

104

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EXPLANATION

Gilo('rt' s d~ t~
a-O.18.0.20rt
o d ~ 0.305 "'"
6d'0.S06","
"'doO.186m"
. d ~ 1. 71 m"

10'
10-3 10.2 10-1
UN IT STREAM POWER. V5. I ~l FOOT .pourms PE R POUND PER SE CONO

FIG. 7.-Relationship Between Measured Total Sediment Concentration and Unit
Stream Power For Different Particle Sizes

1,093 scts of laboratory data and 65 sets of field data is 0.173. The accuracy
in predicting the total sediment concentration for such diversified flow and
sediment conditions is satisfactory. Fig. 5 shows some examples of the comparison
between the measured and predicted total sediment concentrations in accordance
with Eq. 26. Fig. 5 provides an independent verification of the accuracy of
Eq. 26 because none of the data shown in this figure was used in obtaining
Eq.26.
Among other constraints applied to a natural stream, water temperature and
particle size are the two which attract the most attention from hydraulic engineers .1
who are interested in the study of sediment transport. The change of average
water depth may also have some effect on the total sediment concentration.
The effects of the variations of these variables on the total sediment concentration

<03

OPLAN^TIDN

_R ~ 6.3 - 11.1
I "
-L-R ~6.2 -11.0
- "
_R =5.2-!l.1
"'

d _ 0.23 I~n
[lon.oft
d!" T ~ 5 oC
~T=lSoC
_t,>_T' 25'C

<0'
10-3 10-2 10.1
UNIT STRl^M POWER, VS. IN FOOT-POUNDS PER POUN[l PCR Slcmm

FIG. a.-Effect of Variation of Water Temperature on Predicted Total Sediment
Concentration by Eq. 26

Fig. 8 shows the effect of the variation of water temperature on the predicted
total sediment concentration with d = 0.23 mm and D = 0.5 ft (15.3 cm).
This figure shows that the predicted total sediment concentration decreases
with increasing water temperature for higher values of shear velocity Reynolds
number R u' As the value of R u decreases, the effect o~ the change of water
temperature on the predicted total sediment conce?tratlon tends to reverse:
This is in general agreement with the conclusion obtamed ~y Taylor and Van~~1
(28). This conclusion is supported by Franco's (5,17) and Taylor and Vanom s
(27) data as shown in Fig. 9. .
Fig. 10 shows the effect of the variation of water depth on the predicted