The first definition of debris flow was highlighted by Stiny as a flood of mountain torrents, carrying suspended load and transporting quantities of bedload. Therefore, the source of this water flow needed to be established.Ī 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. 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.
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. This value is not considered high for Malaysian condition. 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. 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. The study area has experienced at least four debris flow incidents, which are concentrated at an initiation zone. The shallow fractured granite is virtually “floating” above the water saturated zone and therefore is considered unstable. 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 weak layer is relatively thick with an estimated thickness of 80 m and water flow occurs at the base of it. The residual soil layer is relatively thin at zones where weathered granite dominates the slope face of the failure mass. These zones are continuous as they have been detected in both the east-west as well as the north-south lines.
The existence of low resistivity zones within the granite body is interpreted as highly fractured, water conducting zones.
A granite body was detected at the central part of the east line and is nearest to the ground surface along FH02. The parallel lines are FH01, FH02, and FH03, while the lines FH04 and FH05 are perpendicular. The study involves three slope parallel survey lines and two lines perpendicular to the slope face. 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).
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