Prediction of channel width based on basin area and river incline and considering geology

Norio Harada, Kana Nakatani, Yoshifumi Satofuka, Takahisa Mizuyama

Monday 29 june 2015

17:30 - 17:33h at Mississippi (level 1)

Themes: (T) Sediment management and morphodynamics, (ST) Sediment transport mechanisms and modelling, Poster pitches

Parallel session: Poster pitch: 3A. Sediment - Erosion

Prediction of sediment runoff in a mountain watershed is an important factor in assessing the potential environmental impacts of a river system, such as deposits at a dam or a sediment disaster. Numerical models of sediment runoff have been investigated by many researchers, and previous research developed numerical models that describe the system of rainfall runoff (flood and sediment runoff). Predicting sediment runoff correctly using these models requires consideration of geological data for upper-stream channels. However, these channels are often narrow and steep. To compile information for a model of these mountainous channels, interpretation of aerial photographs was used. Unfortunately, forest obscures many mountainous channels, resulting in loss of data, including information on the width of the channel. Previous research discussed river widths in Japan and abroad, considering the discharge flow and environmental factors, and proposed a method for designing a river structure model that considers the surrounding environment. The method was well suited to the large rivers in Japan and Canada. However, the study considered alluvial rivers only and did not address differences in geological type that may affect variation in the riverbed. There is a need for a new method of predicting channel widths in mountainous watersheds that accounts for geology type. This paper shows the relationship between channel width and other factors using a statistical analysis technique, termed “mathematical quantification theory class _,” for data from over 800 mountain streams. It was shown that channel width was strongly related to the area of the upper basin, the geological type, and the river cline. Additionally, relationships between channel width and the basin area and river incline based on the results of a statistical analysis of existing stream data were employed to compile geographical feature data in a mountainous watershed for a numerical model to predict sediment runoff. The average correlation coefficient of the proposed relationship R was 0.82 (range, 0.69–0.96); the proposed method was confirmed to be valid for a channel in a mountainous watershed.