Cooper Creek, Australia

Principal Investigators:
Dr. Melba Crawford, University of Texas
Dr. Vic Baker, University of Arizona

Background
The Cooper Creek study site of Queensland's "Channel Country" is part of the immense complex of low-gradient, multichannel ephemeral rivers that occur in southwestern Queensland (Baker, 1986b). This is a very low relief region, but is subject to rare, immense floods. The river system has a combination of meandering, straight , and braided reaches, as well as multichanneled stretches which are said to be anabranching.. Although they are less common than single channeled systems, anabranching rivers occur across a range of environments from alpine streams with steep gradients to low gradient flood plains and deltas. These are the last major category of alluvial system to be described and explained [Nanson and Knighton, 1996].

Cooper Creek drains the tropical humid highlands of the Great Dividing Range, occasionally delivering huge floods to the semiarid and arid interior [Baker, 1986c]. Baker [1986a, p. 6] used Landsat imagery to map the extent of the January 1974 flooding in this region when a flow of 4000 m3/s was estimated for Innamincka. In 1990 flood levels rose to record levels in the Channel Country, submerging over 220,000 km2, constituting a short-lived inland sea [Gale and Bainbridge, 1994]. Stream channels in this area are remarkable for their wide, shallow anastomosing patterns [Rust and Nanson, 1986]. Gradients are very low, only 0.2 m/km [Rust, 1981]. The sediment type is mostly clay, producing unusual mud braids that result from transport of the clay as sand-sized pedogenic aggregates [Nanson et al., 1986]. The landscape also preserves a long Quaternary record of paleohydrological change [Nanson et al., 1988].

The channel trend for Cooper Creek displays control by the late Tertiary deformation of the underlying Cretaceous and Tertiary sediments of the Great Artesian Basin [Baker, 1986c]. Silcrete, a duricrust weathering profile, is developed on the resistant upwarped areas between the active stream channels [Senior and Mabbutt, 1979]. The rivers were probably gradually shifted and locally superimposed as the structures formed. Thus, they show important fluvial response indicators relative to active tectonic deformation. Schumm [1986] outlines additional fluvial indicators for active tectonics, including channel patterns, gradient changes, and terrace deformation.

Data for Proposed Study
Remotely sensed SPOT panchromatic data were acquired over the Eastern Cooper in 1996. One ERS image from November 1995 has been acquired of the river system, and a second has been ordered. Two JERS scenes and a RADARSAT image (scan mode) of the area have been requested for the study. Fully polarimetric 3-channel AIRSAR and 6-channel Thermal Infrared Multispectral System (TIMS) data were acquired during the November 1996 JPL PacRim campaign, one along the main channel of the Cooper and the other in the Strezlecki. The Cooper flooded in March, 1997 . Near concurrent Landsat, SPOT, and ERS imagery of the flood conditions have been requested in conjunction with another study.

Field studies have been conducted by O'Neill and Nanson in the Cooper and the Strezlecki in 1996. Extensive trenching indicated the presense of paleochannels in both areas. A vegetation survey was conducted, and sediment samples for moisture and sediment size were collected coincident with the airborne radar and TIMS overflight. Additional field studies of the sites are planned by O'Neill, Nanson, and Crawford in May and July 1997 after preliminary analysis of remotely sensed AIRSAR and TIMS data.

Analysis to be conducted during the proposed study