Assessing and mitigating large wood‐related hazards in mountain streams: recent approaches

Abstract

The assessment and mitigation of floods in mountain streams, when large wood (LW) is transported, pose several challenges. The process chain consisting of flood propagation, LW recruitment, entrainment, transport, and entrapment triggers, at critical sections such as bridges, unexpected and exacerbated impacts to the exposed built environment. We provide a review on the recent advances in modelling LW dynamics during extreme river floods through computational approaches. Moreover, we describe how scaled flume experiments can enhance process understanding at critical flow sections such as bridges to address risk mitigation problems. Additionally, we present a framework based on Formative Scenario Analysis (FSA) to allow for expert knowledge integration and to subsequently derive consistent hazard process scenarios in steep mountain streams where the application of computational approaches is less reliable. Finally, we discuss how the application of the presented set of assessment methods can support integral flood risk management by explicitly considering LW dynamics since the effectiveness of mitigation critically depends on the acquired process understanding.

Geomorphic and stream flow influences on large wood dynamics and displacement lengths in high gradient mountain streams (Chile)

“…Consequently, to take advantage of the benefits of LW and to prevent its potential negative impacts in the case of floods, natural LW dynamics must be managed properly (Mao, Andreoli, Iroumé, Comiti, & Lenzi, ; Mazzorana et al, ; Wohl et al, ). However, our understanding of wood entrainment and deposition processes is still limited (Dixon & Sear, ; Schenk, Moulin, Hupp, & Richter, ) and largely restricted to a small number of field‐based (Ravazzolo, Mao, Picco, & Lenzi, ); laboratory (Welber, Bertoldi, & Tubino, ); or modelling (Ruiz‐Villanueva, Wyżga, Hajdukiewicz, & Stoffel, ) approaches, typically hampered by short measurement periods and a limited number of tagged logs.…”

“…Consequently, to take advantage of the benefits of LW and to prevent its potential negative impacts in the case of floods, natural LW dynamics must be managed properly (Mao, Andreoli, Iroumé, Comiti, & Lenzi, 2013;Mazzorana et al, 2017;Wohl et al, 2016).…”

Managing Infrastructure in the Stream Environment

“…Wood poses a hazard to infrastructure by racking during floods, reducing flood conveyance of stream crossing infrastructure, and compromising navigation channels. As such, it has historically been removed from streams (Wohl 2014) Risk analysis can aid managers in deciding where and when it is acceptable to leave large wood in streams , Mazzorana et al 2018. Engineered wood structures are increasingly used for habitat restoration and channel stability (Brooks et al 2004;Pess et al 2012).…”

In‐channel wood‐related hazards at bridges: A review

“…A substantial need therefore arises for a better understanding of the effects and interactions of in‐stream wood and bridges. Mazzorana et al () recently provided a review on advances in modelling wood dynamics in rivers, both numerically and experimentally, on a larger scale from the recruitment to the entrapment process and how those methods can support flood risk management.…”