Analysis of debris flow underground sound by wavelet transform - a case study of events in aiyuzih river

Abstract

Since 2002, the Soil and Water Conservation Bureau, which is responsible for the conservation and administrative management of hillside in Taiwan, has been cooperating with Feng Chia University. Together, they have successively carried out the establishment and maintenance of 17 debris flow monitoring stations over the Taiwan and 3 mobile debris flow monitoring stations. Geophone is one of the most important sensor to detect whether debris flow occur or not. The wavelet transform is employed in this study to analyze the underground sound of debris flows obtained from the geophones. Three debris flow events observed at Shenmu monitoring station (Nantou County) on July 2, 2004 and on August 8, 2009 are selected as examples. It is found that the wavelet transform not only can separate ambient noise effectively but also can be used to determine the beginning time of debris flow event. In order to estimate the magnitude of debris flow event, a so-called wavelet accumulated energy indicator is proposed. When debris flow occurs, the wavelet accumulated energy will increase. So the wavelet accumulated energy’s threshold value is double of normal value. It can be used to determine the occurrence of debris flow and to estimate its magnitude.