Page - 363 - in Book of Full Papers - Symposium Hydro Engineering

observation methods for estimating the volume of sediment from the watershed, that will be useful for the sediment management in dam. 2. OUTLINE OF STUDY SITE 2.1. OUTLINE OF STUDY SITE The study site in Omukawa River is located at the top of the Kofu alluvial fan, left branch of the Kamanashigawa, Fujikawa River system, a rapid river with an average gradient 1/58 and an extension of 16.4 km. The study area corresponds to about 8.3 km of its downstream section (Fig. 1). The upstream area consists of low to middle mountains composed of granite and volcaniclastic materials. Within this river section, about 50 Sabo dams and groundsels exist in the channel. Fig. 1 Sediment discharge observation site map 2.2. IMPLEMENTATION OF SEDIMENT DISCHARGE OBSERVATION In order to observe the volume of sediment discharge from the mountain stream, sediment discharge measurement is continuously carried out from 2011 by several equipment, such as hydrophone, turbidimeter, water level gauge, suspended load sampler, and a buried sediment trap pit, etc., on the 50th groundsel in Omukawa River. The layout of observation site and a sample of obtained data is shown in Fig. 2 and Fig. 3 respectively. The annual volume of sediment discharge calculated from the observed data is shown in Fig. 4. Tokyo Yamanashi 363