Author(s): Nobuhide Koi, Yasunori Muto, TAKAO TAMURA

Linked Author(s): Yasunori Muto, TAKAO TAMURA

Keywords: Forest dilapidations; Precipitation; Sediment yield; Exponential functions; Threshold;

Abstract: Due to forest dilapidations in recent years, river basins located in such conditions encounter not only the increases of sediment yield and inflow during the normal period but the rise of collapsing risk during the flooding time. Thus how a degree of forest dilapidation affects the sediment yield and inflow should be clarified. In this study, aiming to derive a sound relation between rainfall and sediment discharge, in the Nishidani And Kumanogawadani River Basin, a tributary of the Tonda River, which is a class B river in Wakayama Prefecture, Japan. The measurement period was from June 2014 until November 2017 in the Nshidani River Basin. Local rainfall and river water levels were measured by setting a rain gauge and several hydro gauges. Sediment discharge in the river was measured by a pit. In addition, from June 2016 through November 2017, we performed similar measurement in the Kumanogawadani River Basin near the Nishidani River Basin as the comparison area where the vegetation condition is different. As a summary of the observations, in each basins, we could show an exponential function in the relationship between the accumulated precipitation and the quantity of sedimentation. Moreover we could find that it has the threshold in rainfall and quantity of sedimentation changes big around the threshold. Furthermore, we showed the possibility that we could grasp quantitatively the influence of the difference by tree species and management state of the forest on the sediment discharge.

DOI: https://doi.org/10.3850/38WC092019-0973

Year: 2019