Sensitivity of bed load transport in Harris Creek: Seasonal and spatial variation over a cobble‐gravel bar

Abstract

Abstract. Bed load sediment was caught in pit traps at several locations on a bar in Harris Creek, a cobble-gravel stream with a nivally dominated hydrograph, a structurally highly organized bed, and very low rates of bed material transport. Observations were made during two spring freshets. In order to obtain representative grain size distributions of the material in transport, the traps were left for periods of up to 24 hours, so that samples of up to 30 kg were recovered. We examine the sensitivity of bedload flux to flow variations via trap-specific ratings for narrowly defined textural subranges. All the ratings are very sensitive, indicating that bed load flux remains in the regime of "partial transport." The ratings also exhibited seasonal hysteresis and varied from trap to trap and from year to year.

A Comparison of Coarse Bedload Transport Measured with Bedload Traps and Helley-Smith Samplers

“…This was true even at the highest flows of 140 % Q bkf (with 250 % Q bkf typically being the highest flow recorded within 60 years). A flattening of the rating curve at high flows that has been reported in some studies, e.g., [2,60,66,71], did not occur in these slightly incised, steep, coarse-bedded, armored, and supply-limited mountain streams.…”

“…The resulting wide range of transport rates provides steep rating curves with high exponents. The range of particle sizes collected in a sampler does not appear to affect the rating curve steepness in these streams: samplers in Table 3 that collected gravel only [65,3,4,66,67,68,69] have similarly steep bedload rating curves as those samplers that also collect sand and fine gravel [70,71]. If rating curve steepness is unaffected by truncation of the lower end of the sampled size distribution, then fractional rating curves (except for perhaps the largest one or two size classes) must be parallel to each other.…”

Causes and effects of noise in landscape dynamics

“…A practical implication is that the relation between sediment flux and fluid stress is probably nonunique, which could contribute to the large scatter commonly observed when attempting to fit a single bed load transport equation to data. It seems likely that some of the hysteresis (e.g., the lag in seeing an effect of a change) observed in bed load response to floods [Hassan and Church, 2001;Hsu et al, 2011] is due to aging.…”

The effects of floods and sockeye salmon on streambed morphology.

“…This is likely to occur once every few years as shown in Hassan and Church (2001) Harris Creek study. It appears that the concept o f initiation o f bedload transport in streams is still largely an open question in fluvial morphology that needs to be studied further.…”

“…In addition, highly unsteady flow can increase sediment transport rates (Phillips and Sutherland 1989). Variation in sediment transport at equal discharge is called hysteresis and many o f these have been described in field studies (Moog andWhiting, 1998, Hassan andChurch 2001 (Naden 1988, Gomez andChurch 1989).…”