An Analysis of Flow Velocity Profiles, Stream Bed Roughness, and Resistance to Flow in Natural Gravel Bed Streams

by Normand E. Bergeron, Universite du Quebec, Sainte-Foy, Canada,

Document Type: Proceeding Paper

Part of: Hydraulic Engineering


The characteristics of 82 flow velocity profiles were analyzed from nine different gravel bed stream reaches. A statistical test of the linearity of flow velocity profiles indicates that contrary to what is frequently assumed, velocity profiles are often not semilogarithmic but segmented - that is, they can be divided in two (or more) semilog-linear segments. The results show that segmented velocity profiles are not confined to streams with very coarse bed material, but that they also occur in streams with relatively small bed particles. Segmented velocity profiles were modeled using a technique called spline modeling. This technique allowed the objective identification of semilog-linear velocity profile segments and of the corresponding knots where they join. An analysis of the pattern of flow over natural bed obstacles revealed that velocity profile segments correspond to distinct layers of the flow adjusted to different scales of roughness: a grain roughness scale controlling the shape of near-bottom velocity segment and a bedform roughness scale controlling the shape of the segment located immediately above.

Subject Headings: Velocity profile | River and stream beds | Flow measurement | Fluid velocity | Bed materials | River flow | Hydraulic roughness

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