FLOOD02997

• County: Statewide
• Basin: Statewide
• Title: Scour and Fill in Steep, Sand-Bed Ephemeral Streams
• Date: 4/1/1978
• Prepared By: University of Missouri-Columbia
• Floodplain - Doc Type: Floodplain Report/Masterplan

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M. G. FOLEY

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~~ TRANSITION 2
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40 50 60 1'0 eo 90 100

MEAN VELOCITY-V {em/seel
Figure 7. Depm versus velocity curve for run F-l~l1.

change between each poine is reduced by me [Otal change, 0.031
em, divided by the number of poims. This linear correcrion assigns
the same error to each point and results in a curve with the
minimum positive mean-bed elevation change during the run.
Howc:ver, [he largest errors in mean-bed elevation change between
points should occur during the early phase of the flow when trans-
parr rare and rransport-rarc fluctUations are the greatest. The
solid-circle poims in Figure 63 show an adjusted curve in which a
body shifr 01 +0,031 em has been made to the initial point. This
adjustment assigns aU of the error to the first !TIcasurernent interval
and results in a curve with the maximum positive mean.bed eleva-
cion change during che run. Spreading me error over the first five or

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MIN. BEDFORM
TROUGH L'.ELEV -I
(em) -2

15

fb/f~

10

5

Figure 8. Data summary
plot fot run F-l-ll.

I
0.7
0,6
0,5
Ib 0.4
0.3
0,2
0,1
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1.3
II
F 0,9
0.7
0,5
0,3
0

10

ten points is more realistic and would result in a "true" curve ir'
ruled area berween the two adjusted curves. A sense of propor
in the magnified vertical-scale plot (Fig. 6a) is provided by a ~
grain shown ro scale. For this equilibrium run, maximum mean
elevation change during the Rood is bur one to tWO sand-g
diamete~ of fill foHowed by scour to the initial mean-bed e1eval
By comparison, Figure 6b shows unadjusted F-l-11 data plorrel
a less-exaggerated vertical scale along with maximum depth of
reworking by bed forms plotted to the same scale. This l
reworking depth was measured as the minimum elevation of
bottoms of bed-form troughs seen in cross section against the fll
window. Bed-form trough depths in the center of rhe channel, I
ticularly amidunes, will be considerably greater rhan the ones n
sured at the window. Figure 6b shows clearly thar mean-bed ell
cion Rucruations are less than 3% of bed reworking by bed fo
when the worsr-case adjusred data are used.
The fill-and-scour rather than scQur.and-611 style of mean-
elevation changes needs consideration, since it does nor agree \'
the classical concepr of bed behavior. Two probable causes
mean-bed elevation fluctuations - the arbitrary sediment-inpul
larion and unsteady-flow effects - will be considered by mean
pertinent laboratory data.
Effect of Sediment.lnpur Relarion on Mean-Bed Elevation
havior. Steady-srare experiments, thar is, ones in which wa
discharge and sediment-input rares are constant, were conducte\
invesrigate me behavior of rhe sand and the channel used in cr
experimenrs. It was found that equilibrium conditions prevailed
sready.state flow with water discharge of 7,500 cm3fs
sediment-input tate of 41.1 cm3/s at a slope of O~l06. At this sl.
and lesser sready.state discharges, the sediment-transport rate
hayed as Cst cc QIS-t..

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