Skip to Main Content
Defining phases of bedload transport using piecewise regressionAuthor(s): Sandra E. Ryan; Laurie S. Porth; C. A. Troendle
Source: Earth Surface Processes and Landforms. 27: 971-990.
Publication Series: Scientific Journal (JRNL)
Station: Rocky Mountain Research Station
View PDF (418.43 KB)
DescriptionDifferences in the transport rate and size of bedload exist for varying levels of flow in coarse-grained channels. For gravel-bed rivers, at least two phases of bedload transport, with notably differing qualities, have been described in the literature. Phase I consists primarily of sand and small gravel moving at relatively low rates over a stable channel surface. Transport rates during Phase II are considerably greater than Phase I and more coarse grains are moved, including material from both the channel surface and subsurface. Transition from Phase I to Phase II indicates initiation and transport of grains comprising the coarse surface layer common in steep mountain channels. While the existence of different phases of transport is generally acknowledged, the threshold between them is often poorly defined. We present the results of the application of a piecewise regression analysis to data on bedload transport collected at 12 gravel-bed channels in Colorado and Wyoming, USA. The piecewise regression recognizes the existence of different linear relationships over different ranges of discharge. The inflection, where the fitted functions intersect, is interpreted as the point of transition from Phase I to Phase II transport; this is termed breakpoint. A comparison of grain sizes moved during the two phases shows that coarse gravel is rarely trapped in the samplers during Phase I transport, indicating negligible movement of grains in this size range. Gravel larger than about D16 of the channel surface is more consistently trapped during Phase II transport. The persistence of coarse gravel in bedload samples provides good evidence that conditions suitable for coarse grain transport have been reached, even though the size of the sediment approaches the size limits of the sampler (76 mm in all cases). A relative breakpoint (Rbr ) was defined by the ratio between the discharge at the breakpoint and the 1.5-year flow (a surrogate for bankfull discharge) expressed as a percentage. The median value of Rbr was about 80 percent, suggesting that Phase II begins at about 80 percent of the bankfull discharge, though the observed values of Rbr ranged from about 60 to 100 percent. Variation in this value appears to be independent of drainage area, median grain size, sorting of bed materials, and channel gradient, at least for the range of parameters measured in 12 gravel-bed channels.
Data archive: http://dx.doi.org/10.2737/RDS-2007-0003
- You may send email to email@example.com to request a hard copy of this publication.
- (Please specify exactly which publication you are requesting and your mailing address.)
- We recommend that you also print this page and attach it to the printout of the article, to retain the full citation information.
- This article was written and prepared by U.S. Government employees on official time, and is therefore in the public domain.
CitationRyan, Sandra E.; Porth, Laurie S.; Troendle, C. A. 2002. Defining phases of bedload transport using piecewise regression. Earth Surface Processes and Landforms. 27: 971-990.
Keywordsbedload transport, gravel-bed channels, Phase I and Phase II transport, piecewise regression, breakpoint
- A tutorial on the piecewise regression approach applied to bedload transport data
- Sediment transport data and related information for selected coarse-bed streams and rivers in Idaho
- Measurement of coarse gravel and cobble transport using portable bedload traps
XML: View XML