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<br />llYDRAULlC ENGINEERING ...
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<br />Collection or Dala
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<br />Belween AugusI 1990 and November 1993, dal. w~re collecled from flows alii
<br />sites on stream channels in central Arizona. These sues were selc.cted to repre~nl
<br />a wide range of channel conditions and riparian environments. SIX of the 11 sues
<br />coincided with sites in a field manual for estimating. Manningls roughness
<br />coefficienls in Maricopa County, Ariwna (Thomsen and HJalmarson, 1991).
<br />
<br />Average vegelation heighl was measured and classified .s either brush (O.5.to 3.0 m
<br />in heighl) or Irees (3.5 to 6.0 m in height). Dominanl specIes of vegelabOn were
<br />mesquile, saJlCedar. wiDow, and collonwood. The effeel of peak flow on '~e
<br />channel vegelalion was classified as eilher (I) no effccl, (2) hl~C e.ffccl,. (3) laId
<br />over or (4) removed. The lenn,/aidover, is defined as rhecondll1on In w.hlch mosl
<br />'. . 50 fr h ru.caJ Discharge was oblalned from
<br />vegetation IS bent more than 4 om I e vc. . .
<br />eilher . nearby U.S. Geological Survey streamflow-gaging slallon Ihat had a
<br />well-deCmed slage-<lischarge relation or by indirecl measurement (Dalrymple and
<br />Benson 1976). MOSI s....am channels in lhis sludy are ephemeral and are
<br />compos'ed prcdominandy of gravel-to boulder-size malerial. A summlU)' of d.,.
<br />for each of Ihe 13 flows is given in lable I.
<br />T.b" 1. Summary of Uoodllow and vegetation data collected horn stream channels in central
<br />Arizona
<br />
<br /> - A_-
<br /> ....... 0....,.. _. Ellecl
<br />.... O....t In..... deKrlpllon holgh.. on__
<br />num- '...811.... lIo. ....... of In ....n
<br />... ,.. ......- .....,.
<br /> .-nd
<br /> VIlntc River _ ScuIu4aJc 00.21-91 11.0 ~uedbnldl "0 ......
<br /> ." SaillCUdbnu.h ,.0 l.aidovcr
<br /> Do. 01.24-92
<br /> Do. OI.OII.l}] '.... ..........- ,.0 l...Uduvcf
<br /> Shllk Cndt abcNc hilum. 11 00.01-91 11.S MQdcmc: hrwh ... ......
<br />Z
<br /> ~M Raul Wuh abqw; Curly lB.06-9] "0 St;aucrtdbNlh 1.0 Li""
<br />,
<br /> ....
<br /> AIIIII:riI, RiYCt below WAddeU 01.09-9] 1SS MOOcltlCbrush z., IJuIc
<br />.
<br /> """
<br /> Ilauayampt. Riverncu AdinltOll OI.Q8.g] '" MPdcn&c bnllh Z.O l.aiduvef
<br />, Satucrlldlrces. .., Liuk::
<br /> Do.
<br /> SaIlKivuabovcIruentaae10 01.08-9] 3,110 Sc:aUCRd bnuh ,., I...i<luver
<br /> . Scauucdl,", s.s l-iltk
<br /> 0..
<br /> Cave CIuk abowe New RWu Road 01-0&-9] ]16 ~lCbrulh "0 Rcn,u'~oJ
<br /> 1 ScauCfcdlfCCS '.0 IJuk
<br /> 0..
<br /> New River IIbovc Ink:mac 11 01.08.9] ". Muduu&: brush z.o RclPD'lcd
<br /> . Scau"odll~a OJ) l.aiduva
<br /> Do.
<br /> 1111I'Y.,.llilterReaf Wickenbw& 01-08-91 141 MudcfJ&cbllllh l.s RCAltIVW
<br /> . ............, s.s I-AiJ.....,
<br /> Do.
<br /> '-oneil Cnd: M'" Wikieup 01-08.9] '" Mudcr.tClreel .., I...Wuvcr
<br />'0
<br /> 8iISanolyR.ivcrne.l,[W"'~ 02-()lJ.93 1,9S0 Scaucwl bn&sh ,., l.aiduvcr
<br /> II DenIC~cII 'S.O NllfIc'
<br /> Do.
<br />'u....fotGllerhNllr;._.
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<br />FLOODFLOW EFFECfS-ARIZONA
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<br />109
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<br />Data Amtlvsis and Intemretation
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<br />Slream power is a measure of energy transfer (power per unit area of streambed)
<br />and has been used to estimate flow regime for alluvial channels by relating stream
<br />power and median grain size to fonn of bed roughne.. (Benson and Dalrymple,
<br />1984). S....am power is computed by lhe fonnula
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<br />SP = 9,800RSV,
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<br />where:
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<br />9,800 = $.pecific weight of walCf, in Newtons per cubic hle&cr;
<br />R = hydraulic rokfius, in melers;
<br />S = Wiler-surface slope, in meleJ'S per meter; and
<br />V Mean ve1ocilY, in meletS per second.
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<br />Computed s....am power for rhe 13 flows is given in table 2. Stream power was
<br />computed al cross scctions and plolled againSllhe average height of vegelation for
<br />each flow (fig. I). Cross sections generally were uniform in shape and did not
<br />require subdividing except for the section at Big Sandy River near Wikieup, which
<br />was panhandle in shape and required subdividing to account for nonunifonn
<br />velocilY dislribulion (Thomsen and Hjalmar,un, 1991). As shown in figure I, Ihe
<br />effecl of f100dflow on vegelalion condition is relaled to vegetation height and
<br />compuled stream power. If stream power is small, it may have no observable effecI
<br />on riparian vegelation; however, as stream power increases, the vegetation is laid
<br />over and uhimalely can be removed. Larger amounls of stream power are needed
<br />10 Ilffcclthe laller vegetation. A stream power of about 74 (N-m/s)Im' is needed 10
<br />I.y over Ihe 1.0-meter-high brush, and a s....am power of about 580 (N-m/s)/m'is
<br />needed to layover the S.5-metcr-high trees. In addilion, as indicaled by the
<br />upper-Icn pan of figure I, lhe s.....m power nccessary to remove vegelalion is five
<br />ro six limes greater than the Stream power necessary to layover lhe vegelation.
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<br />The relalion shown in figure I is similar 10 a relation between rhe product of
<br />vclocily and hydraulic radius and Ihe effecI of flow on grasses defined by rhe Soil
<br />Conservalion Service (1954). The same relation was investigaled for the stream
<br />channels of this Study; however, use of the water-swface-slope term in the
<br />s....am-power equation appeared to improve rhe relation.
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<br />Need. for Funher Studv
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<br />The effecls of f100dflows 00 riparian vegelalion need 10 be sludied funber. The
<br />effccls of channel scour, vegelation deasily and duralion of f100dllow will be
<br />sludied. Dala on vegetation stiffness, which would increase our underslanding of
<br />lhe effects of f100dflow on vegelalion, also would be of v.lue.
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