Planform geometry and channel migration of confined meandering rivers on the Canadian prairies

The planform geometry and migration behaviour of confined meandering rivers at 23 locations in Alberta and British Columbia are examined. Relationships among planform geometry variables are generally consistent with those described for freely meandering rivers with small but significant differences because of the unique meander pattern of confined meanders. These exceptions are the ratio channel wavelength (l)/channel width (w) and the bend curvature (rm/w); in these confined meanders, the ratios exceed (l/w ≈ 17; rm/w = 4.1) the free-meander norms (l/w = 8–14; rm/w = 2–3). In general, these migrating confined meandering rivers do not develop cutoffs, and meander bends appear to migrate downstream as a coherent waveform. Migration rates vary greatly, from 0.01 to 5.8 m/y, consistent with the general distribution of published rates for freely meandering rivers. Attempts to seek correlations between migration rate and channel flow and morphometry data are modestly successful. Stream power offers the best statistical predictor of migration rate, accounting for up to 52% of variance in migration rate, greater than that provided by valley slope (34%), bankfull width (32%), and mean annual flood (30%). Overall, the findings indicate that confined meandering rivers within western Canada may be more usefully regarded as part of a continuum of a meandering river pattern rather than as a unique river planform.