Debris flow monitoring in the Acquabona watershed on the Dolomites (Italian Alps)

In 1997 a field monitoring system was installed in Acquabona Creek in the D olomites (Eastern Italian Alps) to observe the hydrologic conditions for de bris flow occurrence and some dynamic properties of debris flow. The monito ring system consists of three remote stations: an upper one located at the head of a deeply-incised channel and two others located downstream. The sys tem is equipped with sensors for measuring rainfall, pore pressures in the mobile channel bottom, ground vibrations, debris flow depth, total normal s tress and fluid pore-pressure at the base of the flow. Two video cameras re cord events at the upper channel station and one video is installed at the lowermost station. During summer 1998, three debris flows (volumes from les s than 1000 m(3) up to 9000 m3) occurred at Acquabona. The following result s were obtained from a preliminary analysis of the data: I) All of the flow s were triggered by rainfalls of less than 1 hour duration, with peak rainf all intensities ranging from 4.8 to 14.7mm/10 minute. 2) Debris flows initi ated in several reaches of the channel, including the head of the talus slo pe. 3) The initial surges of the mature flows had a higher solid concentrat ion and a lower velocity (up to 4 m/s) than succeeding, more dilute surges (more,than 7 mis). 4) Total normal stress and pore fluid pressures measured at the base of the flow (mean depth about 1.1 m) were similar (about 15 kP a), indicating a completely liquefied flow. 5) Peak flows entrained debris at a rate of about 6 m(3)/m of channel length and channel bed scouring was proportional to the local slope gradient and was still evident in the lower channel where the slope was 7 degrees. (C) 2000 Elsevier Science Ltd. All rights reserved.