Occurrence of cluster microforms in mountain rivers

Abstract

The occurrence of cluster microforms in natural rivers is examined using data collected from three mountain streams. The study was conducted under the premise that the occurrence of clusters is strongly tied to local reach-scale conditions, and that prediction of clustered sites therefore can be made through identification of particular reach conditions that are conducive to cluster development. For the study, reach-scale variables were measured at 50 sites and the presence or absence of clusters at each of these sites was recorded. A statistical analysis using logistic regression was performed to examine the correlation between the occurrence of clusters and various combinations of reach-scale parameters. It was found that clustering was best predicted by the bankfull channel width scaled with the d 84 of the bed sediment, w/d 84 , and the non-dimensional parameter wQ 2 /gd 6 84 . It is thought that these variables work best at predicting the presence of clusters because they are descriptive of the reach hydraulic and sedimentary conditions and work well at discriminating between reach morphology types. It was found that clustering was most strongly tied to riffle-pool type reaches. Observations from this study suggest that clusters can be described as bed features that form out of the structural organization of grains in cobble-size sediment within depositional mountain reaches, for which the majority of the sediment can become mobilized by yearly peak flows.

The role of hydrologic processes and geomorphology on the morphology and evolution of sediment clusters in gravel-bed rivers

“…3) supports the correlation of clusters with reach-average parameters found within steeper gradients and riffles, that satisfy a predictable range of sedimentary and hydraulic conditions (Strom and Papanicolaou, 2009). The results point out the role of the geomorphic settings surrounding the river channel in determining the sediment characteristics that control the formation and stability of sediment clusters.…”

Gravel threshold of motion: a state function of sediment transport disequilibrium?

“…Many studies have explored the bed state control of stabilizing structures formed by coarse grain clusters (e.g., Church et al, 1998;Strom and Papanicolaou, 2009). Other bed state controls include the degree of overlap, interlocking and imbrication among grains, and bed compaction or dilation (e.g., Parker, 1990;Wilcock and Crowe, 2003;Sanguinito and Johnson, 2012;Buscombe and Conley, 2012;Mao, 2012;Kirchner et al, 1990;Marquis and Roy, 2012;Powell and Ashworth, 1995;Richards and Clifford, 1991;Ockelford and Haynes, 2013).…”

Laboratory study of gravel‐bed cluster formation and disintegration

“…The aim of the present study is to investigate the development of naturally formed clusters from a flattened bed of graded gravel at constant flow rate. These experiments act as a bridge between the group of laboratory experiments conducted on idealized glass spheres [e.g., Papanicolaou and Schuyler , ] and field studies conducted on naturally formed clusters [e.g., Billi , ; Hendrick et al ., ; Strom and Papanicolaou , ; Brayshaw , ; Reid et al ., ]. Field studies are often limited by the practicalities of continuously monitoring bed conditions during flood events.…”