Downstream hydraulic geometry of clay-dominated cohesive bed stream channels

Abstract

Empirical downstream hydraulic geometry equations for clay-dominated cohesive bed (semi-alluvial) streams were derived using the data from five streams in eastern Ontario and four streams from other regions. The width exponent (0.57) is comparable to the exponents reported for previous studies; however, depth exponent (0.52) was greater for clay-dominated cohesive bed than for typical gravel-bed and sand-bed rivers. Furthermore, the recurrence intervals of bankfull discharges of those streams range from 1 to 2 years. To the author's knowledge, this is the first study which related bankfull hydraulic variables and discharges to derive downstream hydraulic geometry equations specifically for clay-dominated cohesive bed streams. Assessment of width:depth ratio depicted that large channels were deeper and narrower than comparable gravel-bed channels, but small channels were actually wider and shallower than typical gravel-bed rivers. This can likely be attributed to the resistance of stiff and consolidated cohesive-bed to erosive effects of more frequent flows.