The Monitoring and Flow Dynamics of Gravelly Debris Flows at Houyenshan Gullies(2/2)

The mechanisms of rainfall-induced landslides and debris flows in Houyenshan gravelly gullies will be explored in this proposed study in a three-year period (2014-2017, while 2014-2015 was approved and an ongoing project), by mainly employing field study and experimental work. The field monitoring system will be implemented on an expanding modular base, which includes the rainfall gauge, geophones and infrasound sensors, ultrasound range- detector and video recording system, respectively. The previous monitoring system was destroyed by rainfall-induced debris flows on July 13, 2013 (Typhoon Suli). Through the newly advanced monitoring system, we can first examine the threshold rainfall conditions for landslides and debris flows in gravelly gullies. The acoustic signals in response to the magnitude and flow patterns of gravelly debris flows will be analyzed, which are important information for the warning and evacuation processes for the debris flow prone areas. In the first year (2014/8〜2015/7, being an ongoing project): The analysis of hydrological data and geomorphological data of Houyenshan gravelly gullies will be analyzed. This study collects the available rainfall data and geographical data of Houyenshan gullies by using 3D Lidar. A rainfall gauge with data logger will be installed in the first Gully of Houyenshan. The threshold rainfall condition for landslides and debris flows will be evaluated consequently. In the second year (2015/8〜2016/7): The acoustic signals and monitoring systems of gravelly debris flows: The acoustic and geophone signals will be analyzed. The acoustic characteristics of landslides and debris flows in the gravelly gullies in response to the flow patterns and magnitudes of the debris flows will be evaluated. The significant frequencies related to the granular and liquid content will be further studied with experimental work. In the third year (2016/8〜2017/7): The magnitude of debris flows related to the rainfall and geomorphological conditions of gravelly gullies: we will expand the field monitoring system with the video recording system. Through the acoustic sensoring techniques and the information provided by the completed monitoring system, the flow velocity and the discharge of the debris flow events related to the rainfall condition, as well as the geomorphology of the gravelly ravines can be obtained. The relationship between the landslides and the debris flows can be further studied with the aforementioned information and the field survey.