7371

• UCREFRP Catalog Number: 7371
• Author: Stalnaker, C. B., R. T. Milhous and K. D. Bovee.
• Title: Hydrology and Hydraulics Applied to Fishery Management in Large Rivers.
• USFW Year: 1989.
• USFW - Doc Type: D. P. Dodge, ed. September 14-21, 1986.
• Copyright Material: YES

.

T,...BLE 3. power l'(X'ffi.:ienh In certain channel l1](\rrh"l{)g~ n:la-
tions,

CoefficIent Kan~as" Albenac Saimon Rl\n. ID' Average
m 0.16 0.14 0,12 0,14
f 0,31 0.33 0.34 0,33
b 0.54 0,53 0.54 0,54

'Streamflow exceeded 10 % of the time (from Burns 1971),
"Two-year flood flow (from Bray 1982),
'Annual peak with a I in 2-yr return period (from Emmett 1975).

TABLE 4. Percent decrease in cenain characteristics of stream
morphology resulting from reduction of peak streamflows.

Morphology
factor

Power"
coefficient

50
9.2
19.2
31.2
14.1

Percent reduction in peak flow

10
1.5
3.3
5.5
2.2

33
5,5
12.2
19.6
8,5

0,14
0.32
0.54
0.22b

Velocity
Depth
Width
Width/depth

'From Table 3.
bCoefficient for width minus coefficient for depth.

remarkable, considering the geographic diversity of the
streams. However, when regressions are performed on
streams conforming to a different set of conditions, different
relationships could be anticipated.
Whereas hydraulic geometry equations might be predic-
tive in a situation where only the flows changed, they would
not be well suited to an application where both the flow and
the sediment load were modified. This concept is illustrated
in Table 5, based on data from the North Platte River and
the Platte River in Nebraska (Williams 1978). In this case,
the change in width is greatly underestimated, most likely
because the analysis did not account for a change in sedi-
ment load and size nor the encroachment of riparian vegeta-
tion.
Using the results of a laboratory study by Raju et al.
(1977) for variable sediment discharge and constant water
discharge we obtained the following relations:
(II) v=QsO.1O
(12) d = Qs -0,12

(13) It' = Q,U02
114) 5 = 0,043
(IS) lI"d=Q,i'I."
where S is the slope. and Q. is the sediment discharge; the
other terms as defined previously, The study was made at
nearly constant discharge and used particles :s 0.27 mm in
diameter.
Three interesting points were developed in this study: (l)
the major impact of a change in the sediment load with no
change in streamflow was on the slope; (2) the width did
not change significantly with a change in sediment load; and
(3) the depth decreased with an increase in sediment load.
In most rivers, the slope cannot increase without the river
becoming straighter. Sinuosity - the ratio of the channel
length to the valley length - decreases with an increase in
sediment load. In addition, the meander wave length
increases.
Schumm (1977) suggested the following generalized rela-
tionships :
(16) Q = II (width, depth, meander wave length,
I1slope)
(17) Qs = 12 (width, I/depth, meander wave length,
slope, l/sinuosity)
where Q is the streamflow and Qs is the sediment load.
In many water development projects, both the sediment
load and the streamflow may be changed. The direction of
change suggested by Schumm (1977) is illustrated in Table
6 to show channel changes expected from specified changes
in sediment loads and streamflow.
When a reservoir is constructed, the impact on both the
sediment load and the. peak flows is significant. From
Table 6 we would expect the width of a river to decrease
after decreasing both the discharge and sediment load.
Actual results from 16 projects (Table 7), illustrate some
inconsistencies with these generalities. The width increased
in II (which is not the expected change) and decreased is
5 (the expected result).
Hay (1982) provided the following equations to use with
mobile gravel bed rivers.
(18) P = ~.20 QO.54 Qs -0,05
(19) R = 0.161 00.41 D50-0.15
(20) dm = 0.252 00,38 D50 -0,16
(21) S = 0.679 Q-O,53 Qso,13D50o,97

TABLE 5. Comparison of estimated vs. observed change in channel width of the North Platte and Platte rivers. Nebraska, using the
hydraulic geometry equations.

Base condition Modified condition Ratio:
Mean peak Mean peak
flow' flowb Estimated' Observed Actual!
Location (m3.s -I) Width (m) (m3.s-l) width width estimated
Sutherland 152 410 68 265 75 0.28
North Platte 217 520 72 282 90 0.32
Brady 218 340 100 223 45 0.20
Cozad 204 440 84 324 40 0.12
Ovenon 293 1520 140 1020 335 0.33
Odessa 196 930 165 506 490 0.95
Grand Island 312 730 174 545 760 1.39
'Peaks between July 1927 and March 1939.
bpeaks between October 1957 and 1970.
<Estimated width = width (1938) x (Q(l965)/Q(l938)) expo 0.54. Data source: Williams (1978).

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