An experimental study on surface runoff and sediment discharge on a slope covered with fine-grained volcanic ash

Abstract

The purpose of this study is to clarify changes in surface runoff characteristics and sediment discharge on a granule ash-covered slope. Three years after the latest eruption of Unzen volcano, we made an observation of surface runoff and sediment discharge on a slope of the volcano. We scattered fine-grained volcanic ash in one-third area of the slope in June, 1999. As a result of the ash-covered treatment the following points were found.
(1) It was considered that the volcanic ash covered on the study slope was washed away from the slope by surface runoff as suspended sediment.
(2) The peak discharge and total amount of surface runoff after the treatment increased under the approximately similar rain conditions.
(3) The decrease in the surface runoff and sediment discharge resulted from disappearance of the volcanic ash on the surface of the slope.
It is concluded that the runoff characteristics of the study slope had changed with the covering and the movement of fine-grained volcanic ash.