124 / 2024-02-17 18:57:08

Development of Evaluation Model for Driftwoods Generation in the Kawabe River basin and Assessment of the Effect of the Climate Change

logistic modle,driftwoods,climate change,heavy rain

During the heavy rainfall in July 2020, 15,883 m³ of floating debris was collected in the Ariake Sea and Yatsushiro Sea, Kyushu, Japan from July 4th to 31st. This fact means that approximately 12 times of floating debris which is normally collected in just one month. If driftwoods are discharged into a coastal area, they will have serious effects on fisheries and marine ecosystem. Also, driftwoods accumulated under the bridge will make rivers overflowed. In this way, driftwoods affect various fields and regions, so it is necessary to evaluate the risk of driftwoods generation. The Japan Meteorological Agency uses the snake lines as a criterion for determining landslide warning information. The snake line is depicted by plotting the relation between the 60-minute cumulative rainfall and the soil rainfall index at regular intervals. If the snake line exceeds the landslide occurrence reference line (Critical Line: CL), it is judged that the risk of landslides become to be high.

In the present research, we attempt to conduct the followings: i) to confirm whether the snake line in a geographical mesh with the slope collapse exceeds CL in the heavy rainfall in July 2020; ii) to develop the logistic model for predicting the amount of driftwood generation adding the information of CL; and iii) to assess the effect of the climate change by applying d4PDF to the model.

As a result, we can see the followings: 1) the snake line can show the slope collapse by correcting the present CL; 2) in the case of a future climate with increase of 4℃ mean air temperature, compared to the present climate, amount of driftwood generation will increase by approximately 1.2 times. It is necessary to improve estimation of possibility using CL for precise real time prediction of driftwoods generation.