Development of channel organization and roughness following sediment pulses in single-thread, gravel bed rivers

Madej, Mary

A study conducted by a Research Geologist with the U.S. Geological Survey. Excerpts: "Large, episodic inputs of coarse sediment (sediment pulses) in forested, mountain streams may result in changes in the size and arrangement of bed forms and in channel roughness. An understanding of bed form development at several scales is important because bed forms provide resistance to flow and consequently influence flow properties. [This study] focuses on changes in channel structure, organization, and roughness accompanying high supplies of coarse sediment to forested, mountain streams, based on boundary conditions, channel gradient, the presence of forcing elements, and the number and magnitude of flows capable of mobilizing bed material (called 'organizing flows'). Several study reaches were located in Redwood Creek and its tributary Bridge Creek in the northern Coast Ranges of California. Lost Man Creek, a tributary of Redwood Creek was also included. Analyses based on results from other studies (e.g. on Smith, Gwynn, Cape, and Little Cummins Creek; and Higashigochi and Navarro Rivers) were also used. Typical channel changes following a sediment pulse were initial decreases in water depth, in variability of bed elevations, and in the regularity of bed form spacing. Trajectories of change subsequently showed increased average water depth, more variable and complex bed topography, and increased uniformity of bed form spacing. Bed form spacing in streams with abundant forcing elements developed at a shorter spatial scale (two to five channel widths) than in streams without such forcing mechanisms (five to 10 channel widths). Channel roughness increased as bed forms developed."

Development of channel organization and roughness following sediment pulses in single-thread, gravel bed rivers

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