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<br />J
<br />
<br />,#
<br />
<br />568
<br />
<br />M. G, FOLEY
<br />
<br />
<br />reported similar resulrs for flow depths as much as 30 em from ex.
<br />perimems in the 200.( (61~m) flume at Colorado Stare University.
<br />Nordin's (1964) observations of flows in the upper flow regime on
<br />the Rio Grande, which were used above in discussion of the QU3ral
<br />Creek flows, included flows as much as 1. 7 m deep with suspended
<br />~dimen[ concentrations up to 7.16 X 10" ppm. Thus, for uniform
<br />sand.bed ephemeral channels (relatively straight channels with
<br />nearly rectangular cross secrions and lacking pools and riffles), the
<br />results of these field and laboratory experiments should apply for
<br />flow depths of less than 2 m, provided that channel slope is steep
<br />enough to insure upper flow regime throughout [he runoff evenr.
<br />An example where this latter requiremenc is nor met is given in the
<br />next section. For channels lacking rectangular cross sections, hav4
<br />ing irregular widths along a reach, or with pools and riffles,
<br />analysis of f1o.w parameters may require the slope4area technique
<br />(Dalrymple and Benson, 1968). This technique will be valid so long
<br />as nows are hydrodynamically tough (Henderson, 1966, p, 97) and
<br />will give the maximum flow conditions necessary for estimation of
<br />maximum antidune height as well as mean flow conditions. Again,
<br />this procedure is limited by lack of field data on anridunes to flows
<br />less chan 2 m deep:
<br />For steep streams with depths greater than 2 m, results of these
<br />experiments may not apply. Work in progress on steep ephemeral
<br />Streams in the volcanic highlands of Guatemala suggeStS mar eirher
<br />debris~flow underflows or macroturbulence may be imporranr in
<br />nows of 3-m depth Ot greatet. Distriburions of boulders and boul-
<br />det bars in the Rio Guacalate (R. K. Vessell, 1976, otal commun.)
<br />rdative to channel width and gradient variations are not inCOmpa[4
<br />ible with transport by m.,!crorurbulence such as discussed by Baker
<br />(1973). However, some kind of laharic or other density underflow,
<br />such as proposed by Leopold and others (1964), cannot be ruled
<br />our at this time.
<br />
<br />SCOUR AND FILL IN THE
<br />ARROYO DE LOS FRIJOLES
<br />
<br />Observations of scour and fill by Leopold and others (for exam,
<br />pie, ~opold and ochers, 1966) have involved numerous scour4
<br />
<br />100
<br />
<br />i=
<br />
<br />50
<br />~ 0 MeOyo 00 '0'
<br />
<br />::rn-
<br />
<br />~ f-
<br />~ o.SOt
<br />
<br />~ 020'
<br />r
<br />~
<br />w
<br />00,10
<br />
<br />FrilOles
<br />
<br />-
<br />
<br />-rIO~/ I
<br />TranSItIon' Q:)
<br />
<br />-<>
<br />
<br />/
<br />/
<br />0/
<br />'-0
<br />
<br />DunesJ
<br />
<br />chain measurements in the Arroyo de los Frijoles in New Mexico. If
<br />the experimenral results reported here arc of gencrJI'applic;J.bilitv
<br />then bed-form amplitudes for flows in the Arroyo de 10s Frijol~~
<br />should be of the same size as the recorded scour and fill.
<br />For che purpose of comparison. antidune amplirude will be calcu.
<br />lated for appropriate nows in the main project reach of [he Arroyo
<br />de los Frijoles (Leopold and others, 1966). Relevanr channel data
<br />for this fC;J.ch are mean sediment size = d~, = 0.7 mm (Leopold and
<br />ochers, 1966, Fig, 149), channel widch = w = 24 co 30 m (80 co
<br />100 fr) (Leopold and ochers, 1966, Fig, 148), and channel slope = 5
<br />= 0.0177 (Leopold and Miller, 1956. App, AI.
<br />Leopold and others (1966, Table 4, Fig. 1591 reporred average
<br />scour-chain measurements of scour and fill as functions of
<br />maximum discharge, which was determined ac a gaging sration.
<br />Row depths were noc reported. so flow estimation using equations
<br />1 and lb is nor possible wichout some modificarion.
<br />If the flows are assumed to be fuIly rough and in me anridune
<br />flow regime - assumptions which can be checked once /low
<br />paramete.cs are calculated - chen the grain-roughness Darcy-
<br />Weisbach friction factor can be written in the fonn (Rouse, 1946):
<br />
<br />(f.) I = 2 log ( :.. ) +1.74 (7'
<br />
<br />Also, for a stream in which width is much greater than deprh,
<br />r -== d, and unit discharge can be written:
<br />
<br />q = ,v, (81
<br />
<br />where V is mean flow velociry. Subsriruring equations 7 and 8 imo
<br />equacion 1 results in a relarion between V and q:
<br />
<br />11'" = (8gqS)' [2 log ( .;: ) + [,74 - log V' ] , 19:
<br />
<br />Equarion 9 can be solved graphically to find V for a flat bed for a
<br />given unit discharge. Then, the antidune amplirude range can be
<br />calculated using equations 2b, 4J 5. and 6. Results of these compu.
<br />tations for the main project reach of the Arroyo de los Frijoles are~
<br />shown in Figure 10, along with Leopold and ochers' (1966, Table
<br />4) mean scour4chain data on scour versus q. ,{::
<br />1f."
<br />/':
<br />
<br />o
<br />
<br />Figure 10. Depth of scour as a funroon of '
<br />unit disdlarge (Leopold and others, 1966), and
<br />calcul2ted antidune amplitude in main project.
<br />ream, Arroyo de los Frijoles, New Mexico. Each
<br />plotted POlnt rcprcsmts an avuage scour acroSS '
<br />me channel, based on dara from 4 to lO scour-'
<br />chains.
<br />
<br />(~7;
<br />-;0-1:"__
<br />,":C
<br />/J"
<br />...'::;
<br />
<br /> /
<br /> / /
<br /> 0 /
<br />005
<br /> I 0 ; I
<br /> 0 0
<br /> o. 00
<br />002
<br />00\
<br />002 005 0'" 020 050 '0 20 50 '00 200 500 "'00
<br /> UNI T DISCHARGE (cls"ll
<br />
<br />:J
<br />
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