# Predicting Alluvial-Fan Sediment-Water Slurry Characteristics and Behavior from Sedimentology and Stratigraphy of Past Deposits

*by*Jeffrey R. Keaton, Hauskins & Beckwith, Salt Lake City, United States,

**Document Type:**Proceeding Paper

**Part of:**Hydraulics/Hydrology of Arid Lands (H²AL)

**Abstract:**Slurry characteristics can be predicted by a combination of field and laboratory analyses. Field observations are needed to determine deposit stratigraphy and to estimate the abundance of clasts too large to evaluate in the laboratory (> 50 mm diameter). Laboratory analyses are needed to estimate (1) clast density, (2) grain size distribution, and (3) water content at which the slurry matrix becomes fluid. Laboratory grain size distributions can be corrected for large (> 50 mm diameter) clasts to reflect the characteristics of the actual slurry rather than the matrix only. Slurry density can be calculatedx from matrix water content at the laboratory threshold of fluid behavior and the abundance of coarse clasts. Flow velocity can be estimated from the geomorphology of deposits in super-elevated curves; velocity gradients can be estimated from the geomorphology of alluvial fans beyond canyon mouths. Flow inertia and impacts forces can be estimated from flow velocity, slurry density, and clast diameters. The principal law of engineering geology is 'the recent past is the key to the near future'. Deposits comprising alluvial fans document the characteristics of recent flows; therefore, future flows should be expected to create similar deposits. Analyses of alluvial-fan sedimentology and stratigraphy provide a geologic basis for calibrating engineering models.

**Subject Headings:**Slurries | Fluid velocity | Stratigraphy | Density currents | Water content | Matrix (mathematics) | Sediment | Grain (material)

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