HR: 09:05h
AN: H51F-04    [Abstracts]
TI: The Regulation of Peace River: a Large-scale Experiment on Fluvial Governing Conditions
AU: * Church, M
EM: mchurch@geog.ubc.ca
AF: The University of British Columbia, Department of Geography, Vancouver, BC V6T 1Z2 Canada
AB: In 1967, British Columbia Hydro and Power Authority closed W.A.C.Bennett Dam, creating what was then the sixth largest hydropower project in the world. The dam is located in the Rocky Mountain front range so that, although it controls about half the runoff of the 293 000 sq.km basin, almost all of the sediment load originates downstream from the dam in the Alberta Plateau. Hence, the effects of these two principal governing conditions of fluvial systems can be separated. The 378 km immediately downstream to the Smoky River confluence are a wandering, cobble-gravel reach It has effectively ceased to be alluvial and the channel pattern has been simplified. Aggradation is occurring at major tributary junctions, whilst the tributaries themselves have degraded in their lowermost reaches. Smoky River, the principal tributary, delivers a large sand load. The 250 km reach to Carcajou is sandy gravel and the final 600 km to the Peace-Athabasca delta is sand-bed. Aggradation, with a change in fluvial style toward low-order braiding, appears to be underway in the proximal sand-bed reach. More generally, channel shrinkage in response to the regulated flow regime is controlled by the rate of progradation of riparian vegetation onto former bar surfaces In 1996, after 29 years of regulated flow, reservoir drawdown for dam repairs led to full spillway flows for 8 consecutive weeks, creating an effectively bankfull condition in the proximal post-regulation channel. Significant degradation was observed for the first time in many cross-sections but overall changes were surprisingly modest, reflecting the refractory bed and the degree to which riparian vegetation has become firmly established in former channel areas. Overall, sediment supply and flow competence are the principal controls of fluvial response in the system. The experimental aspect of this study of a large, northward flowing, boreal river can be controlled by before-after comparison. However, this strategy must take into account a changing hydroclimate which has seen increased precipitation but decreased winter snowfall, the latter being the chief source of runoff. However, it can also be pursued by comparison with Liard River, of comparable scale and morphology, located to the north. In both rivers, winter ice regime represents a significant additional dimension for study.
DE: 1803 Anthropogenic effects
DE: 1815 Erosion and sedimentation
DE: 1824 Geomorphology (1625)
DE: 1860 Runoff and streamflow
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting