[A-CG42] Water and sediment dynamics from land to coastal zones

[ACG42-P10] Development of a sediment yield estimation model using the RUSLE model and sediment delivery ratio in Japan

Katsuragi Haruka¹, Keiko Udo², *Rika Okitsu³ (1.Department of Civil and Environmental Engineering, Graduate School of Engineering, Tohoku University, 2.Department of Civil and Environmental Engineering, Tohoku University, 3.Department of Civil and Environmental Engineering, School of Engineering, Tohoku University)

Keywords:sediment yield, RUSLE, sediment delivery ratio, future projection

It is difficult to solve problems caused by several factors in the whole sediment system, such as riverbed change, by taking measures only in that area. Therefore, we should have a comprehensive sediment management system that manages and controls the sediment system as a whole. It is important to quantitatively assess the sediment yield (SY) that flows into the river from collapsed upstream areas in order to assess the actual condition of sediment dynamics in the river basin. The objective of this study is to develop a sediment yield estimation model suitable for Japan to quantitatively evaluate sediment yield in upstream areas and to predict future sediment yield in the whole of Japan. In this study, SE is calculated using the RUSLE model and SY is calculated by multiplying the SE by the SDR equation newly proposed in this study. We adopt the SDR equation with the watershed area as a variable, and newly determine empirical parameters α and β in the equation.

In the flow of this method, SE is first calculated using the RUSLE model, and the measured annual average sediment deposition in the dam is used for SY. By taking the ratio of both, the SDR value for each upstream dam basin is obtained. The empirical parameters α and β in the equations are then determined by plotting the watershed area on the horizontal axis and fitting the shape of the power function. 64 upstream end dam basins on first-class rivers in Japan were selected for the analysis, and the period of analysis was from 2006 to 2019. The SY was considered as the sediment inflow into the dam by dividing the annual average sediment deposition in the upstream end dam by the capture rate E in order to introduce into the riverbed change model. The results showed that α = 0.157 and β = -0.238 when the capture rate was considered.

Then, we projected future SY for each upstream end dam basin using the predicted future rainfall from the d4PDF data. The future SY showed a 1.17-fold increase from 2051 to 2070 and a 1.25-fold increase from 2091 to 2110 compared to the 1991 to 2010 period.