How do stream processes affect hazard exposure on alluvial fans? Insights from an experimental study

作     者：Bruno MAZZORANA Elisa GHIANDONI Lorenzo PICCO Bruno MAZZORANA;Elisa GHIANDONI;Lorenzo PICCO

作者机构：Universidad Austral de ChileFaculty of SciencesInstituto de Ciencias de la Tierra5090000 ValdiviaChile Universidad Austral de ChileRINA–Natural and Anthropogenic Risks Research Center5090000 ValdiviaChile Universidad Austral de ChileLaboratory of HydromorphologyFaculty of Forest Sciences and Natural Resources5090000 ValdiviaChile University of PadovaDepartment of LandEnvironmentAgriculture and Forestry35020 LegnaroItaly 

出 版 物：《Journal of Mountain Science》 (山地科学学报（英文）)

年 卷 期：2020年第17卷第4期

页      面：753-772页

核心收录：

学科分类：08[工学] 081501[工学-水文学及水资源] 09[农学] 0903[农学-农业资源与环境] 0815[工学-水利工程] 

基　　金：Project FONDECYT nr.1170657 titled “The flood memory of a river system:using both experimental and field-based approaches to unravel the role of unsteady flow and antecedent flows on sediment dynamics during floods” funded by CONICYT and led by Luca Mao Project FONDECYT nr.1170413 titled “Morphological impacts in rivers affected by volcanic eruptions.Chaiten and Calbuco:similar disturbance but different fluvial evolution?(PIROFLUV)” funded by CONICYT and led by Andrés Iroumé 

主　　题：Alluvial fan Hazard Exposure Flood risk Experimental model Process similarity 

摘      要：Alluvial fans are among the most privileged settlement areas in many mountain regions. These landforms are particularly dynamic being episodically affected by distributary processes generated by extreme flood events. Addressing risk assessment entails determining hazard exposure and unravelling how it might be related to process loading and to process dynamics once the flow becomes unconfined on the surface of alluvial fans. By following a ‘similarity of process concept’, rather than by attempting to scale a real-world prototype, we performed a set of 72 experimental runs on an alluvial fan model. Thereby, we considered two model layouts, one without a guiding channel and featuring a convex shape and the other one with a guiding channel, a bridge, and inclined but planar overland flow areas as to mirror an anthropic environment. Process magnitude and intensity parameters were systematically varied, and the associated biphasic distributary processes video recorded. For each experiment, the exposure was detected by mapping the exposed area in a GIS, thereby discerning between areas exposed to biphasic flows and the associated depositional phenomena or to the liquid flow phase only. Our results reveal that total event volume, sediment availability and stream power in the feeding channel, as well as depositional effects, avulsion, and channelization on the alluvial fan concur to determine the overall exposure. Stream process loading alone, even when rigorously defined in terms of its characterizing parameters, is not sufficient to exhaustively determine exposure. Hence, further developing reliable biphasic simulation models for hazard assessment on settled alluvial fans is pivotal.