17:15 〜 18:45
[ACG43-P01] RUSLEモデルを用いた表層土砂侵食量の時空間変化の推定
キーワード：土砂管理、土砂流出、RUSLE、河川の形態変化
Integrated sediment management throughout the entire watershed is necessary to solve sediment-related problems in watersheds. Although a river morphological change model is effective for understanding sediment dynamics in a watershed, hypothesis of equilibrium sediment inflow condition at the upstream boundary still makes it difficult to estimate appropriate sediment dynamics. The objective of this study is to develop a method for estimating spatio-temporal changes in sediment erosion using the RUSLE model, which has few parameters and has been applied to many regions, for employing the results to estimate the sediment inflow at the upstream boundary.
The RUSLE model (Revised Universal Soil Loss Equation) is an empirical soil erosion model developed primarily by the U.S. Department of Agriculture. The amount of soil erosion A determined by the RUSLE model is expressed by the following equation (1), which in this study is the amount of surface sediment erosion.
A=RKLSCP (1)
where A: annual soil erosion [t/ha y], R: rainfall intensity coefficient [MJ mm/ha h y], K: soil coefficient
[t h/MJ mm], LS: topographic coefficient [dimensionless], C: crop coefficient [dimensionless], P: land conservation coefficient [dimensionless]. The rainfall intensity coefficient R is calculated by calculating the rainfall intensity coefficient Ri for an arbitrary rainfall event i, integrating the Ri during the period of interest, and dividing by the number of years to calculate the annual average value. In this study, the time-series change of A is obtained by replacing the total rainfall ri in any rainfall event i used to calculate R by the time-series rainfall ri,t.
The calculation results are compared with the observation data of surface suspended sand obtained at the first weir of the Higashikarasugawa River in Fukushima Prefecture during the Boso Peninsula typhoon of 2019 (Typhoon No.15, September 2019) and the East Japan typhoon of 2019 (Typhoon No.19, October 2019). The calculated data was overestimated three times the observed data but showed appropriate result.
The RUSLE model (Revised Universal Soil Loss Equation) is an empirical soil erosion model developed primarily by the U.S. Department of Agriculture. The amount of soil erosion A determined by the RUSLE model is expressed by the following equation (1), which in this study is the amount of surface sediment erosion.
A=RKLSCP (1)
where A: annual soil erosion [t/ha y], R: rainfall intensity coefficient [MJ mm/ha h y], K: soil coefficient
[t h/MJ mm], LS: topographic coefficient [dimensionless], C: crop coefficient [dimensionless], P: land conservation coefficient [dimensionless]. The rainfall intensity coefficient R is calculated by calculating the rainfall intensity coefficient Ri for an arbitrary rainfall event i, integrating the Ri during the period of interest, and dividing by the number of years to calculate the annual average value. In this study, the time-series change of A is obtained by replacing the total rainfall ri in any rainfall event i used to calculate R by the time-series rainfall ri,t.
The calculation results are compared with the observation data of surface suspended sand obtained at the first weir of the Higashikarasugawa River in Fukushima Prefecture during the Boso Peninsula typhoon of 2019 (Typhoon No.15, September 2019) and the East Japan typhoon of 2019 (Typhoon No.19, October 2019). The calculated data was overestimated three times the observed data but showed appropriate result.