Imbrication of Tabular Boulders

by Cyril Galvin,

Document Type: Proceeding Paper

Part of: Hydraulic Engineering


Analysis of moments on tabular boulders projecting into a uniform stream indicates that a tabular boulder dipping downstream is unstable and can be overturned by velocities expected during storm flows. For a tabular, downstream-dipping, quartz boulder, at least half of which projects above mean bed level, there is a critical overturning Froude number, somewhat less than 3. 0. As a result of this instability, tabular boulders will preferentially dip upstream, overlapping the next downstream boulder where such boulders are abundant. Because this imbrication is a form of streamlining, imbrication, and related preferential orientation of isolated boulders, may explain observed overprediction of friction factor for flows in some mountain rivers.

Subject Headings: Boulders | Fluid velocity | Froude number | Streamflow | River flow | Water flow | Rock mechanics | Mountains

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