Effectiveness of Geoelectrical Resistivity Surveys for the Detection of a Debris Flow Causative Water Conducting Zone at KM 9, Gap-Fraser’s Hill Road (FT 148), Fraser’s Hill, Pahang, Malaysia

This study reports the findings of resistivity surveys which were conducted at the initiation area of debris flow at KM 9, Fraser’s Hill Gap road (FT148). The study involves three slope parallel survey lines and two lines perpendicular to the slope face. The parallel lines are FH01, FH02, and FH03, while the lines FH04 and FH05 are perpendicular. A granite body was detected at the central part of the east line and is nearest to the ground surface along FH02. The existence of low resistivity zones within the granite body is interpreted as highly fractured, water conducting zones. These zones are continuous as they have been detected in both the east-west as well as the north-south lines. The residual soil layer is relatively thin at zones where weathered granite dominates the slope face of the failure mass. The weak layer is relatively thick with an estimated thickness of 80？m and water flow occurs at the base of it. The high water flow recorded from the horizontal drains further supports the possible existence of these highly fractured, water conducting zones located within the granite. The shallow fractured granite is virtually “floating” above the water saturated zone and therefore is considered unstable. 1. Introduction The study area has experienced at least four debris flow incidents, which are concentrated at an initiation zone. One of the debris flow triggering factors in the mountainous terrain of Peninsular Malaysia is high intensity rainfall during or before the debris flow incident. At the time of occurrence of the debris flows in the study area, the intensity of rainfall recorded was between 0？mm/day to 14？mm/day. This value is not considered high for Malaysian condition. The finding is based on the current larger study on seven other sites in Peninsular Malaysia which showed that heavy rainfall is a major triggering factor. However, a Fraser Hill site, incidents of debris flow occurred during low of rainfall intensity and at the same time high water flow was observed. Therefore, the source of this water flow needed to be established. A debris flow is one type of the natural disasters that can be classified as landslides and can cause damage to property and loss of life. The first definition of debris flow was highlighted by Stiny as a flood of mountain torrents, carrying suspended load and transporting quantities of bedload [1]. Sharpe defined debris flow as a rapid flow of saturated or viscous debris in a stream or channel [2]. According to Hungr et al. a debris flow is defined as a very rapid to extremely rapid flow of saturated