Research Interest
International River Interface Cooperative: iRIC
The International River Interface Cooperative (iRIC) was started in 2007 by Professor Yasuyuki Shimizu (Hokkaido University) and Dr. Jonathan Nelson (USGS) with the purpose of (1) developing a software platform called iRIC for numerical simulation of flow and morphodynamics in rivers and (2) providing seminars and educational material to support that software.
Computational challenges on morphodynamics of the Earth surface
We are interested in the morphodynamics of the Earth surface, particularly, rivers, but also estuarine and submarine environments. We have been applying various types of numerical models on the morphodynamic phenomena. You can see our reivew paper regarding this contribution below.
Sand bars, bedforms and their interactions
Bedforms are fundamental piece of the river morphologies and some different types of bedforms in terms of origin and spatial scale could coexist. We have developed several types of numerical models (1D, 2D, 3D) for modeling several types of the bedform dynamics in the rivers.
Modeling bedload tracer transport
An understanding of the detailed mechanisms of bed load transport is of central importance for elucidating a wide spectrum of morphodynamic processes in rivers, as well as the fate of sediment-bound substances such as nutrients, metals, and radionuclides in river systems. Tracer particles that are distinguishable from the ambient bed sediment only via passive markers that do not affect transport dynamics have been widely used to measure and quantify bed load transport. The tracking of tracer particles that are initially deployed on the bed surface provides data regarding temporal and spatial changes in tracer distribution and gives insight into characteristics of bed load transport, such as travel distance and waiting time distribution. Such measurements have shown that tracers advect downstream and disperse in space in the streamwise, transverse, and vertical directions. The collective asymptotic behavior of tracers has been described in terms of advection-dispersion. An understanding of this advection-dispersion sheds light on bed load transport itself, as well as associated bed morphodynamics, and is central to the estimation of how fast and far sediment-bound substances can be transported.
Driftwood transport and deposition in rivers
The quantification of driftwood deposition in rivers is important for understanding the total budget of driftwood at the watershed scale; however, it remains unclear how such driftwood storage in rivers contributes to the overall system because of the difficulties in undertaking field measurements. Herein, we perform numerical simulations of driftwood deposition within an idealized river reach with a sand-bed, to describe the role of large-scale bedforms, more specifically, alternate bars, multiple bars, and braiding, in driftwood storage in rivers. The numerical model we propose here is a coupling model involving a Lagrangian-type driftwood model and an Eulerian two-dimensional morphodynamic model for simulating large-scale bedforms (ie, bars and braiding).