Runoff-generated debris flows: Observation of initiation conditions and erosion–deposition dynamics along the channel at Cancia (eastern Italian Alps) |
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| Authors: | Alessandro Simoni Martino Bernard Matteo Berti Mauro Boreggio Stefano Lanzoni Laura Maria Stancanelli Carlo Gregoretti |
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| Institution: | 1. Department BiGeA, University of Bologna, via Zamboni 67, Bologna, 40126 Italy;2. Land Environment Agriculture and Forestry Department, University of Padova, viale dell'Università 16, Legnaro, 35020 Italy;3. Civil, Environmental and Architectural Engineering Department, University of Padova, via Loredan 20, Padova, 35131 Italy;4. Environmental and Civil Engineering Department, University of Catania, Piazza Università 2, Catania, 95131 Italy |
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| Abstract: | In the Dolomitic region, abundant coarse hillslope sediment is commonly found at the toe of rocky cliffs. Ephemeral channels originate where lower permeability bedrock surfaces concentrate surface runoff. Debris flows initiate along such channels following intense rainfall and determine the progressive erosion and deepening of the channels. Sediment recharge mechanisms include rock fall, dry ravel processes and channel-bank failures. Here we document debris flow activity that took place in an active debris flow basin during the year 2015. The Cancia basin is located on the southwestern slope of Mount Antelao (3264 m a.s.l.) in the dolomitic region of the eastern Italian Alps. The 2.5 km2 basin is incised in dolomitic limestone rocks. The data consist of repeated topographic surveys, distributed rainfall measurements, time-lapse (2 s) videos of two events and pore pressure measurements in the channel bed. During July and August 2015, two debris flow events occurred, following similarly intense rainstorms. We compared rainfall data to existing rainfall triggering thresholds and simulated the hydrological response of the headwater catchment with a distributed model in order to estimate the total and peak water discharge. Our data clearly illustrate how debris entrainment along the channel is the main contributor to the overall mobilized volume and that erosion is dominant when the channel slope exceeds 16°. Further downstream, sediment accumulation and depletion occurred alternately for the two successive events, indicating that sediment availability along the channel also influences the flow behaviour along the prevailing-transport reach. The comparison between monitoring data, topographical analysis and hydrological simulation allows the estimation of the average solid concentration of the two events and suggests that debris availability has a significant influence on the debris flow volume. © 2020 John Wiley & Sons, Ltd. |
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| Keywords: | debris flow runoff initiation rainfall thresholds erosion |
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