RELATIONSHIPS BETWEEN HYDRAULIC VARIABLES AND BEDLOAD TRANSPORT IN A SUB-ALPINE CHANNEL, COLORADO ROCKY-MOUNTAINS, USA

This study used three cross-sections along a subalpine channel to exam ine associations between now and sand and gravel bedload transport in a cobble-bed channel. At each section, velocity was measured at 0.2, 0 .4, 0.6, and 0.8 of now depth for ten increments across the section. A t each increment, velocity measurements were immediately followed by 1 0-min bedload samples with a 7.6 cm Helley-Smith sampler. Linear regre ssions between bedload and flow variables suggest that grain shear str ess, stream power, near-bed velocity, average velocity, and the Froude number are the most relevant indicators of bedload transport, particu larly when regressed against the D-max or D-84 of the bedload grain-si ze distribution. No significant relationships, however, were constant at all three cross-sections. Inconsistency in relationships between be dload discharge and hydraulic variables is at least in part the result of the extreme temporal and spatial variability present in East St. L ouis Creek. Photographs and observations made throughout the field sea son suggest the importance of random events, such as tree-fall and log -jam formation, in regulating bedload discharge. The data from East St . Louis Creek suggest equal mobility for sand and gravel transport. (C ) 1998 Elsevier Science B.V.