HR: 1340h
AN: H53B-0467    [Abstracts]
TI: Velocity profiles and turbulent structure over the sand bed of the lower Strickland River, Papua New Guinea
AU: * Swanson, K M
EM: kswanson@berkeley.edu
AF: Department of Earth and Planetary Sciences, University of California, Berkeley, CA 94720-4767 United States
AU: Bera, M
EM: beram@upng.ac.pg
AF: Department of Geology, University of Papua New Guinea, Port Moresby, 134 Papua New Guinea
AU: Dietrich, W E
EM: bill@eps.berkeley.edu
AF: Department of Earth and Planetary Sciences, University of California, Berkeley, CA 94720-4767 United States
AB: Observations on the suspended sediment profiles on the sand bedded Fly and Strickland Rivers of Papua New Guinea reveal significant variation in sediment concentrations throughout the full range of sizes, including silt and clay. These surprising observations motivated an intensive analysis of the velocity profiles and turbulent structure in these rivers. Here we report the results of a field campaign on the Strickland River. Our measurements were made at 4 reaches along the lower Strickland and one reach of the Herbert River, a tributary that links the Strickland to Lake Murray. The Strickland drains 36,740 sq km, and carries and annual sediment load of about 80 MT. The bed in the study reaches had a D50 of 0.23 mm. Slowly migrating bedforms were present on the bed, and some of the measurements were taken in the lees of bars. The stage of the river was well below bankfull at the time of measurement. We used a RDI Broadband 614.4 kHz acoustic Doppler current profiler to document velocity and turbulence fields. The instrument was mounted on the side of the research vessel, the Western Venturer, and continuous measurements were collected for periods in excess of one day. At the same time, three hundred corresponding suspended sediment grab samples composing 43 full profiles and 11 bed material samples were also collected at these sites. Initial analysis of the flow data indicates that more than 20-minutes of data are needed to accurately sample over the longest turbulent scales. In some cases the flow is highly variable over periods on the order of hours. The mean velocity measured is ~0.5-1 m/s with a friction velocity on the order of 0.1 m/s and depth of flow varied from 4-m to 14.5-m. A variety of profiles were found, but in the simplest cases of velocity measurements in the center of the channel, time averaging produced well-defined logarithmic velocity profiles in the lower 20% portion of the flow. Reynolds stress measurements in this region, however, revealed systematically large and vertically erratic values that record the wake effects of the bedforms. Initial suspended sediment profile data show a correspondingly high concentration of sediment, including the coarsest sediment on the bed, at a distance of up to 2-m from the bed. We are exploring how the velocity and turbulent profile data can be used to test various turbulence closure schemes.
DE: 1825 Geomorphology: fluvial (1625)
DE: 1856 River channels (0483, 0744)
DE: 1886 Weathering (0790, 1625)
SC: Hydrology [H]
MN: Fall Meeting 2005