The Hydraulic Geometry of Peace River: Fid-Bau Portal

The Hydraulic Geometry of Peace River

Church, Michael

Abstract: Hydraulic geometry at‐a‐station is explored using the history of stream gauging at six alluvial sections along Peace River. At long‐established stations at Taylor and Peace Point, comparisons are made between ice cover and open water periods and at these stations, Dunvegan and Fort Vermilion comparisons are made between pre‐ and post‐regulation periods. Additional information is available for stations at Carcajou (pre‐regulation) and Peace River at Alces River (post‐regulation). Periods of observation vary from 7 to 64 years and numbers of gaugings from 29 to 430 (of which 255 are for ice conditions). The most striking change is the increase in sensitivity of the width variable in the post‐regulation period, a consequence of lower flows after regulation in wide, flat‐bottomed channels. This reflects passive adjustment to regulated flows within the preexisting channel. At some stations the 1996 drawdown flood led to incremental dynamic changes in geometry. Some stations exhibit anomalously high rates of adjustment of velocity. The downstream hydraulic geometry is reconstructed by comparing flows of equal frequency at the gauging stations. Adjustment does not follow the general regime relations for Alberta gravel‐ and sand‐bed rivers but, again, reflects passive change. Channels remain wider and shallower than expected. This may be due to slow progradation of vegetation, but ice effects to maintain a wider channel cannot be discounted in the lower river. Peace River sections approximate a general flow resistance relation for channels dominated by grain resistance, except at Taylor and Fort Vermilion, where a developing bar and sandy bedforms, respectively, offer additional resistance. Discriminant functions for channel pattern indicate that the river should dominantly be single thread, as observed.