Toward a Practical Method for Estimating Sediment Transport Rates in Gravel-bed Rivers

Estimates of sediment transport rates in gravel-bed rivers are typically developed from formulae or from a sampling campaign. The former are notoriously inaccurate; the latter require a large effort and may still not achieve acceptable accuracy. A wide range of geomorphological problems, particularly those at the watershed scale, could be addressed more accurately if reliable local estimates of transport rate could be incorporated routinely into such studies. This requires a method for estimating transport rate with acceptable accuracy and a minimum of effort. A consistent approach to estimating transport is not just a matter of which formula or sampler to use; a suitable approach requires a consistent and reliable scaling of the water discharge and an integral description of the sediment that is both meaningful and practical. An approach proposed here, using a few observations of small transport rates to calibrate a transport formula, is likely to provide a superior combination of accuracy and effort and substantially reduces flow-scaling error. Small transport rates can be measured effectively using pit samplers, which allow the sampling periods needed for accurate measurements. Grain size can be represented as two fractions, sand and gravel, which capture some of the important transport dynamics and effectively represent important environmental problems within a tractable methodological approach. The approach is nearly independent of the uncertainty associated with measuring slope and bed grain-size in the field