9317

• UCREFRP Catalog Number: 9317
• Author: Spahr, N. E., L. E. Apodaca, J. R. Deacon, J. B. Bails, N. C. Bauch, C. M. Smith and N. E. Driver.
• Title: Water Quality in the Upper Colorado River Basin, Colorado, 1996-98.
• USFW Year: 2000.
• USFW - Doc Type: Denver.
• Copyright Material: NO

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(Costa, 1984; Johnson and Rodine, 1984) and have a distinctly different
morphology from typical alluvial deposits.

Many classification schemes have been proposed for coarse-
grained sediment flows based on water content during transport (Beverage
and Culbertson, 1964) ,characteristics of the resultant alluvial deposits
(Smith, 1986; Pierson and Scott, 1985), or on assumed rheological models of
flow dynamics (Postma, 1986). Debris flows typically have 15 to 40 percent
volumetric water content compared with 40 to 80 percent for hypercon-
centrated flows and 80 to 100 percent water for streamflows (Beverage and
Culbertson, 1964). The main distinction in this study is the difference
between debris-flow deposits and hyperconcentrated-flow deposits (Beverage
and Culbertson, 1964; Scott, in press) because debris flows can transform
into hyperconcentrated flow with distance from the source area (Pierson and
Scott, 1985). This distinction is important because hyperconcentrated
flows are quasi-Newtonian fluids and debris flows are not.

Debris-flow deposits are differentiated from hyperconcentrated-
flow deposits on the basis of characteristic particle sorting, sedimentary
structures, and inferred rheological properties. Readers are referred to
detailed descriptions of each type of deposit in Smith (1986) and Scott
(1985). Debris-flow deposits are characterized by lack of sedimentary
structures, poor sorting of particles, matrix support of cobbles and
boulders, and, in some cases, inverse fine to coarse grading. Hypercon-
centrated-flow deposits are also poorly sorted but exhibit clast support of
large particles, have weak sedimentary structures, and cannot/transport the
extremely large boulders moved during debris flows. Streamflow deposits
are well-sorted, have imbrieatedclasts and well-developed sedimentary
structures, audare easily distinguished from debris-flow deposits.

Ve studied 36 tributaries of the Colorado River, and all had
characteristic debris-flow deposits (table 1). Kost tributaries have only
debris-flow deposits and inconspicuous hypereoncentrated-flowdeposits;a
few tributaries in the western Grand Canyon (such as HavasuCreek, fig. 1)
have both well-sorted streamflow deposits and debris-flow deposits.
Twenty-one of the 36 tributaries have evidence of debris flows within the
last 25 years, including fresh boulder levees and matrix-supported
deposits. ntis sampling of thenearty 310 ungaged tributaries of the
Colorado River between Lees Ferry and Diam~ndCreek (fig. 1) suggests that
debris flows are a major process of sediment transport from small drainages
to the Colorado River in Grand Canyon_~~~E.1~~~_~I11"Jc. u_~_____

HYDRAULICS or DEBllIS,,' FLOWS

Debris flows have properties important both to hydraulic
calculations and preservation of evidence for past events. Debris flows
are non-Newtonian, or cohesive fluids that co_only move essentIdly as a
plug in high-velocity laminar flow (Enos, 1977; Johnson and Rodine, 1984).
Viscosities for debris flows may be several orders of magnitude higher than
the viscosity of water (Costa, 1984). Particle interlocking in the dense
fluid results in internal friction and shear strength. A. a result, debris
flows have a finite thickness called the critical thi~kne.. at a velocity
of zero. Turbulence 1s dampened 1n the moving fluid (Enos, 1977), which

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