Bankfull and bed load effective discharge in a steep boulder-bed channel

摘要

In order to achieve a better understanding of the physical processes involved in incipient bed load transport and channel-forming conditions in high-gradient streams, bed load rate and flow discharge data provided by the Rio Cordon measuring station were analysed. From 1987 to 2003, 22 floods characterized by bed load transport were recorded at the measuring station. From field surveys, the bankfull discharge was estimated to be 2.3 m3 s-1, with a return period of 1.6 years (lognormal distribution). This is consistent with previous findings regarding the frequency of bankfull conditions. Based on the flow duration curve, bankfull stage is exceeded nine hours per year. The effective discharge for bed load transport, i.e. the flow transporting the greatest amount of bed load over a long period, was estimated to be 2.45-2.65 m-1 s-1, which is close to the estimated bankfull discharge. Uncertainties associated with establishing the effective discharge are identified and discussed.