2021 Volume 77 Issue 2 Pages I_134-I_147
Due to forest dilapidations in recent years, sediment yields from a slope and slope collapsing risk are increased. In addition to devastating sediment disasters such as happened in Kii Peninsula flooding in 2011, continuous sediment runoff following to such disasters causes riverbed aggradation and revetment damage under normal flood period, which seriously threatens safety level of flood control. Thus it is important to clarify the relationship between precipitation and sediment discharge.
In this study, we analysed the relationship in the Otonashi River basin, a tributary of the Kumano River in Kii Peninsula, and tried to derive a critical hourly precipitation, that is effective to yield sediment discharge. From the analyses, the critical hourly precipitation can be found around 15mm/h or 20mm/h. Moreover, by applying the critical hourly precipitation as a cut-off value to the accumulated precipitation, a linear function between the adjusted precipitation and sediment discharge becomes clearer. These concepts were also applied to the observational results in the Nishidani and the Kumanogawadani river Basin, tributaries of the Tonda River adjacent to the Kumano River, then we showed the proposed linear function can estimate sediment discharge in accordance with a rainfall event reasonably well. Although the coefficients of the function vary from one river basin to another, the concept can be useful to estimate sediment deposition within a river section after normal flood roughly but quite easily.
