HR: 16:00h
AN: H24F-01    [Abstracts]
TI: Fine Sediment Residency in Streambeds in Southeastern Australia.
AU: * Croke, J C
EM: J.Croke@adfa.edu.au
AF: School of PEMS, University of New South Wales, Northcott Drive, Canberra, ACT 2601, Australia
AU: Thompson, C J
EM: C.Thompson@adfa.edu.au
AF: School of PEMS, University of New South Wales, Northcott Drive, Canberra, ACT 2601, Australia
AU: Rhodes, E
EM: Ed.Rhodes@anu.edu.au
AF: School of Earth Sciences Australian National University, Australian National Unievrsity, Canberra, ACT 2601, Australia
AB: A detailed understanding of channel forming and maintenance processes in streams requires some measurement and/or prediction of bed load transport and sediment mobility. Traditional field based measurements of such processes are often problematic due to the high discharge characteristics of upland streams. In part to compensate for such difficulties, empirical flow competence equations have also been developed to predict armour or bedform stabilising grain mobility. These equations have been applied to individual reaches to predict the entrainment of a threshold grain size and the vertical extent of flushing. In cobble- and boulder-bed channels the threshold grain size relates to the size of the bedform stabilising grains (eg. D84, D90). This then allows some prediction of when transport of the matrix material occurs. The application of Optically Stimulated Luminescence (OSL) dating is considered here as an alternative and innovative way to determine fine sediment residency times in stream beds. Age estimates derived from the technique are used to assist in calibrating sediment entrainment models to specific channel types and hydrological regimes. The results from a one-dimensional HEC-RAS model indicate that recurrence interval floods exceeding bankfull up to 13 years are competent to mobilise the maximum overlying surface grain sizes at the sites. OSL minimum age model results of well bleached quartz in the fine matrix particles are in general agreement with selected competence equation predictions. The apparent long (100-1400y) burial age of most of the mineral quartz suggests that competent flows are not able to flush all subsurface fine-bed material. Maximum bed load exchange (flushing) depth was limited to twice the depth of the overlying D90 grain size. Application of OSL in this study provides important insight into the nature of matrix material storage and flushing in mountain streams.
DE: 1625 Geomorphology and weathering (0790, 1824, 1825, 1826, 1886)
DE: 1804 Catchment
DE: 1821 Floods
DE: 1895 Instruments and techniques: monitoring
DE: 4558 Sediment transport (1862)
SC: Hydrology [H]
MN: 2007 Fall Meeting