Coarse sediment transport in mountain streams in Colorado and Wyoming, USA

Abstract

Since the early 1990s, US Forest Service researchers have made thousands of bedload measurements in steep, coarse-grained channels in Colorado and Wyoming, USA. In this paper we use data from 19 of those sites to characterize patterns and rates of coarse sediment transport for a range of channel types and sizes, including step-pool, plane-bed, pool-riffle, and near-braided channels. This effort builds upon previous work where we applied a piecewise regression model to (1) relate flow to rates of bedload transport and (2) define phases of transport in coarse-grained channels. Earlier, the model was tested using bedload data from eight sites on the Fraser Experimental Forest near Fraser, Colorado. The analysis showed good application to those data and to data from four supplementary channels to which the procedure was applied. The earlier results were, however, derived from data collected at sites that, for the most part, have quite similar geology and runoff regimes. In this paper we evaluate further the application of piecewise regression to data from channels with a wider range of geomorphic conditions. The results corroborate with those from the earlier work in that there is a relatively narrow range of discharges at which a substantial change in the nature of bedload transport occurs. The transition from primarily low rates of sand transport (phase I) to higher rates of sand and coarse gravel transport (phase II) occurs, on average, at about 80 per cent of the bankfull (1·5-year return interval) discharge. A comparison of grain sizes moved during the two phases showed that coarse gravel is rarely trapped in the samplers during phase I transport. Moreover, the movement and capture of the D 16 to D 25 grain size of the bed surface seems to correspond with the onset of phase II transport, particularly in systems with largely static channel surfaces. However, while there were many similarities in observed patterns of bedload transport at the 19 studied sites, each had its own 'bedload signal' in that the rate and size of materials transported largely reflected the nature of flow and sediment particular to that system. Published in 2005 by John Wiley & Sons, Ltd.

Ecosystem level assessment of environmentally based flow restrictions for maintaining ecosystem integrity: a comparison of a modified peaking versus unaltered river

“…Channel maintenance flows maintain pools, riffles, meanders, and other physical habitats necessary to sustain aquatic ecosystems (Schmidt and Potyondy, 2004). Significant bedload transport in gravel-bed rivers typically begins at discharges approaching bankfull flow (Carling, 1995), and numerous authors have linked the initiation of bedload transport in gravel-bed rivers to some percentage of bankfull flow (Haschenburger and Wilcock, 2003;Ryan et al, 2005).…”

“…A simple method was used to determine flow depth to initiate bed sediment transport, using the critical shear stress equation for motion for a given bed sediment size (in Dubinski and Wohl, 2007, adapted from Komar, 1987). The median grain size (D 50 ) is commonly used in sediment transport calculations; however, Ryan et al (2005) indicated that the movement of the D 16 to D 25 grains from the bed surface corresponded with the onset of channel maintenance flows; these grain sizes are used in the sediment transport analysis. Twenty-four years of daily flow data were examined from Water Survey of Canada gauge 02BD003 (Magpie River near Michipicoten) to determine how often flows occurred to mobilize bed material at MR-T27.…”

A Comparison of Coarse Bedload Transport Measured with Bedload Traps and Helley-Smith Samplers

“…However, the sampler was frequently used in coarse-bedded streams. Examples of large studies include [9,10,[16][17][18][19][20][21][22][23][24][25][26], and this study.…”

Channel morphology and bed-load yield in fluvial, formerly-glaciated headwater streams of the Columbia Mountains, Canada

“…Specifically, it was defined as the intersection (or breakpoint) of the linear relations describing low levels of bed mobility, also termed Phase 1 transport, and high levels of mobility or Phase 2 transport (Jackson and Beshta, 1982;Ryan et al, 2005;Fig. 13).…”