Sampling Techniques for Gravel Sized Sediments

The methods commonly used for sampling the coarser surface layers of gravel‐bed streams are reviewed. It is found that while an areal sample is biased toward the coarser grains compared with a volumetric sample of the same material, the conversion formula suggested by a voidless cube model overcompensates for this effect. A modified version of the cube model that accounts for porosity is proposed. The modified cube model and tests conducted with areal sampling using wax indicate that area‐by‐weight analyses can be converted successfully to the equivalent bulk sieve analyses. The average depth of the wax samples ranged from $D_{65}-D_{91}\text{,}$ increasing with median grain size. The equivalence of the grid by number and bulk sieve analyses is reaffirmed.