Abstract
Subsurface water flow in a gravel bar is closely related to the river environment and stream ecological system. In this study, we investigated the characteristics of subsurface water flow focusing on a gravel bar which has various heterogeneous effects, such as permeability and porosity of gravels, and bar shapes, during normal flow stage. A network of wells was established to measure water table elevations in gravel bars of gravel bed rivers in Tokyo, Japan. Permeability and porosity of subsurface layer were surveyed by considering the relationship with "gravel ratio" as a new indicator. The characteristic results suggested are: 1) the subsurface water almost stop flowing in downstream part of gravel bar based on the consideration of the relationship between the gravel ratio and permeability, and 2) the binary particle groups is effective to present permeability and porosity of gravel bed in actual river. These above mechanisms are verified using by experiments and the numerical simulation model. Thus, this suggested that the water exchange characteristics through both of surface and subsurface layer in the gravel bar are restrictive.
