Detection at the time of occurrence of sediment runoff and hydrological phenomena at that time in the Rokko mountain system

Tadanori ISHIZUKA, Kouji HATTORI, Masakazu KUBO, Taro UCHIDA, Yasukazu KOSUGE, Yoko NAGATA, Ken’ichirou KOSUGI and Takahisa MIZUYAMA

To understand the states of the groundwater level in soil layers and the trough discharge when sediment runoffs occur on a slope, numerous real]time landslide detection sensors have been deployed in a small basin in the Rokko mountain system and the groundwater level in soil layers and the trough discharge have been observed at multiple locations for about six years. During Typhoon No.11in July 2015, real]time landslide detection sensors were activated and the data for the groundwater level in soil layers and the trough discharge at that time was obtained. Consequently, the following was revealed:1) The sediment runoff during Typhoon No. 11 in July 2015 was not a surface failure but erosion and outflow of the surface soil owing to the traction force of stream. 2) The groundwater level in soil layers in the sediment runoff area was the highest groundwater level, causing sediment runoffs with a difference of a few centimeters in the groundwater level. 3) The rainfall that led to the highest groundwater level in soil layers varied depending on the location of the observation hole.

Key wordsFreal]time landslide detection sensor, sediment runoff, time of occurrence, groundwater level, trough discharge