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<br />M. G. FOLEY
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<br />Figure 1. Study area and indo:: map showing locarion of srudy area.
<br />
<br />The flow of such streams undergoes transition from the lower flow viation of 5.2, By Schumm's criterion (1961, Fig. 38) this gcain-s
<br />regime (dune-covered bed) co the upper flow regime (flat-bed or spectrum and the channel cross-section geometry suggest thai
<br />antidune bed form) or vice versa with only small changes of dis- Quatal Creek is stable, neither actively aggrading.nor degrading.,;,
<br />charge (Bcooks, 1958; Colby, 1960). Under these conditions, Mean annual precipiration ar Partiway (Fig. I), the nearesr raioc-
<br />Sl:dimenr-ccanspoft equilibrium may not prevail, and mean-bed gaging sracion currendy operating. was 24.9 em foe the 1931-1960:
<br />scour and fill may be possible. This paper describes a series of field period, with most of me precipitation falling between Decembe;'
<br />and labo(3cory aperirnems in which total bed reworIdng during and April. Summer thunderstorms can ca~ significant runoff, but-
<br />floods in sand-bed ephemeral streams is compared with esriInared no large thunderstorms affeCted upper Quatal Canyon during the
<br />or measured bed-fOrm amplitude. investigarion discus~d herein. All significant tunoff events eX,:,:
<br />curred between November and February.
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<br />FlEW EXPERIMENTS
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<br />Field experiments on SCour and fill were conduered in an ephem-
<br />eral stream in northwest Ventura Couney, 135 km nonhwesr of Los
<br />Angeles, California, in the winters of 1973-74 and 1974-75. A
<br />modificarion of a previously developed scour.and-fiU recording
<br />reehnique (Miller and Lenpold, 1963) was applied [Q a limired
<br />reach of me stream so that the pattern and magnitude of tOtal bed
<br />reworking within that reach could be determined. Conceptually,
<br />mean-bed scour and fill in the study reach could be approximarely
<br />determined by subtracting estimated bed.form scour and fill from
<br />total scour and fill.
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<br />Study Area
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<br />Quatal Creek, an east.side tributary of the Cuyama River (Fig.
<br />I), heads on the west flank of Cerro Noroesre (2,526-m elev) and
<br />drains approximately 111 km! in the Los Padres National Forest in
<br />Kern, Ventura, and Santa Barbara Counties, California (Fig. 2).
<br />Details of the drainage basin are shown on the following U.s.
<br />Geological Survey 7.5' series topographic quadrangles: Sawmill
<br />Mountain, Apache Canyon, and Cuyama Peak. The study area lies
<br />in the Apache Canyon quadrangle. Tertiary rocks cropping oUt in
<br />the drainage upstream of the study area provide sediment from clay
<br />. co cobbles, augmented with boulders from Quaternary pediment
<br />gravel. The geometric mean of the sediment size for the first 10 km
<br />of stream bed above the srudy area is 1.3 mm, with a standard de.
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<br />Investigative Procedures
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<br />
<br />A topographic base map was prepared with plane rable and tel '
<br />scope al.idade of [he test reach at a scale of 1: 1,200 with a contour]
<br />interval of 0.5 m (Fig. 3). The base map was used for prop'.
<br />emplacement of a scour-cord network. Previous investigators, e,m.-,,'
<br />ploying the technique of Miller and Leopold (1963), have used:,
<br />chain of 1. to 2-cm links emplaced vertically in an excavated hol.
<br />and anchored at [he bottom. The chains were arranged either singlj
<br />along the stream centerline and spaced from 150 to 300 m apait..o
<br />in groups mat formed more widely spaced rows across the stte "
<br />with chains from 1.5 to 3 m apan (Emmerr and Leopold, 1963L
<br />In order [0 gain better understanding of the detailed behavio~~
<br />the stream bed during floods, a two-dimensional array of!:r.,
<br />..t".
<br />buried scour-cords (3-mm nylon cord) was installed in the.,...,
<br />reach of Quatal Creek (Fig. 3). Ir was hoped that this arcapiu,
<br />provide scour-pattern data distinguishing mean-bed scour ancff'~
<br />from local scour and fill caused by bed-form migration. The'.aa
<br />consisted of 12 sets of 8 to 10 scour-cords, with a 6-m spacing:{ .',
<br />setS of scour.cords were parallel [Q each ocher and roughly pc
<br />pendicular to the highest banks of the acri'Ve channel. The a~
<br />was locally distorted to avoid a brushy island, since the brU:~
<br />_covered parts probably had nor been appreciably scoured for_~j
<br />. ~f.~
<br />eral yea~. ;.: .'''.~~''
<br />The use of nylon cord for smur indicators was a departure ft?..,
<br />normal practice, where large link chain is used. Experiments b(.!,-
<br />..ot
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