Surface sampling in gravel streams

The accuracy of studies concerning the characteristics of gravel-bed waterways is often dependent upon the techniques used to sample and quantify the material found on the channel boundary. Due to the vertical stratification present in the riverbed, the use of sampling techniques that remove only the particles within a thin surface layer is often necessary. Attributes of clay and grid sampling are considered in the present work. Criteria for determining the minimum sample size for a desirable level of accuracy are also presented. Many of the current surface sampling techniques truncate either the upper or lower size range of particles. Truncation of part of a size distribution not only limits the available information, but can also bias the rest of the distribution. The present work rectifies this problem by proposing the use of a hybrid technique that can sample the entire size range of either dry or submerged bed material. Results of field tests that utilize this new method are described in detail.