HR: 1340h
AN: H53C-1253    [Abstracts]
TI: Differential sediment entrainment theory for the maintenance of pool-riffle sequences: evidence from in-situ measurements of friction angle
AU: * Sear, D
EM: D.Sear@soton.ac.uk
AF: David A. Sear, School of Geography University of Southampton Highfield, Southampton, SO17 1BJ United Kingdom
AU: Booker, D
EM: dobo@ceh.ac.uk
AF: Douglas.J.Booker, Centre for Ecology & Hydrology, Wallingford Maclean Building Crowmarsh Gifford , Wallingford, OX10 8BB United Kingdom
AU: Payne, A
EM: a.j.payne@Bristol.ac.uk
AF: Anthony J.Payne, Centre for Polar Observation & Modelling School of Geographical Sciences University of Bristol University Road , Bristol, BS8 1SS United Kingdom
AB: Theories for the maintenance of the pool-riffle sequences have evolved to include consideration of the nature of the bed sedimentology and how this responds to the different low-flow hydraulic characteristics. According to this theory, high frequency turbulence experienced over riffle surfaces during low discharge result in a distinct packing and surface sediment structure that restricts the entrainment of particles. In contrast, pool sediments do not experience such high frequency turbulent flow, and the sediments are effectively "overloose" in comparison. As a result, the difference in critical shear stresses developed between pool and riffle bed sediments results in greater entrainment rates and transport of sediments from pools, whilst riffle surfaces essentially remain immobile. Evidence for the existence of sedimentological contrasts is relatively well established, but explicit links to the entrainment of particles is still untested. This poster reports a new method for testing the in-situ friction angle distribution of water-worked sediments from submerged areas of the river bed. This permits the quantitative analysis of friction angles and particle exposure from pool and riffle bed surfaces. A physically-based method for calculating critical shears stress is applied and the contrasts between pool and riffle identified. The data confirms the existence of variations between un-worked and water worked sediments and between pool and riffle sediments. The magnitudes of these differences vary over time according to the sediment transport dynamics experienced. The theory of differential sediment entrainment therefore provides a partial explanation for the maintenance of riffle pools in this study.
DE: 1824 Geomorphology (1625)
DE: 1625 Geomorphology and weathering (1824, 1886)
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting