Prediction of discharge from water surface width in a braided river with implications for at-a-station hydraulic geometry

The total discharge of small braided rivers can be monitored nearly continuously using ground-based, orthorectified oblique images and a locally derived relationship between mean water surface width in a reach and total discharge with accuracy of the order of 10%. The width-discharge relationship is nearly linear over the normal range of summer flows measured in this proglacial stream. The width-discharge relation for a given location and channel configuration is transferable to adjacent reaches with different morphology with little loss in accuracy. However, the prospect of a more universal relation for braided rivers is remote because of differences in channel geometry and hydraulics between rivers. The classical at-a-station hydraulic geometry exponent for width in this case is approximately 1.05, which is unique, well above that observed in the few other braided rivers for which this has been derived, and implies almost no change in mean velocity and depth with changing stage.