Downstream Channel Gradation in the Regulated Peace River: Fid-Bau Portal

Downstream Channel Gradation in the Regulated Peace River

Ayles, Christopher P. / Church, Michael

Abstract: Dam construction on Peace River in northern British Columbia and Alberta has significantly reduced peak flows, while leaving sediment delivery to the river largely unchanged. The consequent channel gradation is described, main emphasis being given to the 147‐km reach immediately below the dams. Channel bed elevation changes are assessed from repeated surveys of monumented cross‐sections with average spacing four kilometers, and from specific gauge analyses at eight stations along the 1000 km river. Degradation in the British Columbia reach is minimal and local, in consequence of the naturally armored cobble‐gravel bed and elimination of competent flows. However, degradation was more common during the major flood of 1996. Aggradation has occurred near tributary confluences and below other sediment sources, leading to channel constriction and regrading past the confluence. Consequently, the long profile of the river is becoming stepped, but a new equilibrium gradient has not yet been reached near major tributary junctions. Specific gauge analyses in the British Columbia reach are consistent with the survey results. In the more distal portions of the river, specific gauge analyses identify only small changes. Aggradation is interpreted as a mechanism by which the river can recover competence locally to move coarse sediment introduced by the tributaries. Planform adjustment of the river has been restricted to abandonment of the highest flood channels, most of this change occurring passively immediately after regulation.