Abstract
To improve the prediction accuracy of numerical simulation models of water and sediment transport phenomena in mountainous catchments, we discuss extraction methods of the governing processes, and important site conditions and external forces affecting the governing processes. Results show a relationship between catchment area and water and sediment discharges, as derived from observations conducted at multiple locations within a catchment, can be typed according to differences in the spatial distribution of governing processes and controlling conditions. Elucidating relations between the catchment area and water and sediment discharges at multiple locations within the catchment might reveal the governing processes and controlling conditions of water and sediment transport phenomena. Based on these analyses, we discussed issues and approaches reflecting the observed information related to the spatial distribution of water and sediment discharge in the numerical prediction models. Results revealed (1) the importance of longitudinal observations at multiple streams in a catchment for ascertaining characteristics of the spatial distribution of water and sediment discharges. This study also clarified (2) the importance of cataloging spatial distribution of site conditions and, (3) processes that are and are not be expressible solely by topography, Furthermore, we argued (4) a method of modelling processes that cannot be determined solely by topography.
