POROSITY OF SEDIMENT MIXTURES WITH DIFFERENT TYPE OF GRAIN SIZE DISTRIBUTION

Abstract

Assessing the change in void structure of riverbed material is very important for an ecological issue in rivers. Therefore, we have already developed a framework of the bed variation model available for the analysis of the change of porosity of bed material as well as the bed variation. In this framework, the porosity is assumed to be dependent only on the grain size distribution. Thus, it is necessary to relate the porosity of sediment mixture with the grain size distribution in the model. This study aims to develop a method for obtaining the porosity for different types of grain size distribution. Firstly, grain size distribution of sediment mixture in natural rivers were classified into three types, namely log-normal distribution, Talbot distribution and bimodal distribution, and the parameters on those geometric properties were found out. Secondly, a method for identifying the type of grain size distribution was presented. Thirdly, the relationship between the porosity and the geometric parameter of grain size distribution was obtained by means of a packing model. Finally, the porosity of actual riverbed material was estimated by the presented method. The porosity could be reasonably estimated by means of the presented method and it could be introduced into the bed variation model. Key