Turowski J.M.,Eidgenossische Forschungsanstalt WSL Birmensdorf |
Rickenmann D.,Eidgenossische Forschungsanstalt WSL Birmensdorf
Journal of Hydraulic Engineering | Year: 2010
Several indirect methods have been proposed to measure bed-load transport rates. We analyze the relationships between bed-load transport rates, water discharge, and sensor response and determine what can and what cannot be measured with such sensors. We argue that indirect sensors are in most cases unsuitable to develop a rating curve of bed-load transport rates. Instead, they can be used to estimate sediment yields of individual events as proposed previously. We develop a method to estimate the standard deviations of transport rates and apply it to the field data from the Pitzbach in Austria, where direct high-resolution bed-load transport measurements are available. The method gives good results, depending on the choice of bed-load function used for the calculation. The standard deviations are overestimated by about ∼30%. © 2011 ASCE.
Turowski J.M.,Eidgenossische Forschungsanstalt WSL Birmensdorf
Water Resources Research | Year: 2010
It has been known for a long time that sediment transport rates can vary strongly even if the ambient hydraulic conditions remain steady. In this article, a new approach is described to derive probability distributions of bed load transport rates, starting from the waiting time between the arrivals of individual sediment particles. The formalism should be valid when transport is not dominated by bed form motion. Without any assumptions about the distribution of interarrival times, the approach yields the Birnbaum-Saunders distribution, a two-parameter distribution previously used in lifetime modeling. Observed dependence of mean transport rates on the sampling time and multiscaling are predicted by the distribution. Assuming exponentially and Poisson-distributed interarrival times, the same approach yields the Poisson and the gamma distributions. Using a high-resolution bed load transport data set from the Pitzbach, Austria, the distribution functions are tested on field data. The gamma distribution best describes the data, with maximum deviations of ∼5%. However, the Birnbaum-Saunders distribution may be more useful in certain applications, as it is a general approximation in the proposed formalism and no debated assumptions are necessary for its derivation. Copyright 2010 by the American Geophysical Union.