SEDIMENT TRANSLATION WAVES IN BRAIDED GRAVEL-BED RIVERS

Bed-load transport capacity in braided gravel-bed rivers varies as hydraulic geometry changes downstream. Differences in capacity lead to variations in bed-material storage as a consequence of bed-load transport during floods. In turn, storage changes produce irregular fluctuations in bed-level or sediment translation waves in the bed material. These waves are the mechanism by which bed load is transported in braided and, in fact, all alluvial rivers with variable downstream hydraulic geometry. An approximate expression for wave velocity indicates that annual wave travel distance can be hundreds of meters or more per year for waves up to 0.5 m high. Although sediment waves cause shifts in bed-load rating at a cross section, bed-load yield may still be estimated using bed-load ratings based on depth-discharge relations defined for periods between rating changes. A procedure is given for stable channel design in the presence of sediment waves based on equivalence of yield for some period in the design reach and a stable reference reach. The condition that the bed-load ratings for the two reaches must intersect either aids or allows solutions of the design problem.