River widening in mountain and foothill areas during floods: Insights from a meta-analysis of 51 European Rivers

Ruíz-Villanueva, Virginia; Piégay, Hervé; Scorpio, Vittoria; Bachmann, Annette; Brousse, Guillaume; Cavalli, Marco; Comiti, Francesco; Crema, Stefano; Fernández, E.; Furdada, Glòria; Hajdukiewicz, Hanna; Hunzinger, Lukas; Lucía, Ana; Marchi, Lorenzo; Moraru, A.; Piton, Guillaume; Rickenmann, Dieter; Righini, Margherita; Surian, Nicola; Yassine, R.; Wyżga‬‬, Bartłomiej

doi:10.1016/j.scitotenv.2023.166103

Cited by 12 publications

(3 citation statements)

References 80 publications

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“…Perennial vegetation can instead encroach and stabilize less frequently disturbed areas, either due to their higher elevation compared to the thalweg (islands and banks) or their distance from the fast flood flows occurring in the channel (floodplain and terraces). Vegetated surfaces are nonetheless inundated regularly during flood events but are subject to important geomorphic changesexcluding the case of progressive bank erosion-only during high-magnitude, infrequent events [43]. The capability to remotely monitor changes in the relative proportion of these three macro-units in proglacial rivers enables us to understand how water and sediment fluxes are being modified by the progressive deglaciation, as well as by variations in the magnitude and frequency of rainfall events.…”

Section: Methodological Approach and Workflowmentioning

confidence: 99%

Supervised Geomorphic Mapping of Himalayan Rivers Based on Sentinel-2 Data

Mukhtar,

Bizzi,

Comiti

2023

Remote Sensing

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The Himalayan region is a hotspot in terms of expected future hydrological and geomorphological variations induced by climate change on proglacial areas and the related implications for human societies established along the downstream rivers. Due to the remoteness of the proglacial zones in the Himalayas and the associated logistical problems in carrying out traditional field and UAV-based morphological monitoring activities, remote sensing here plays a crucial role to monitor past and current fluvial dynamics, which could be used to anticipate future changes; however, there has been, so far, limited research on morphological changes in Himalayan proglacial rivers. To address this gap, a morphological classification model was designed to classify recent changes in Himalayan proglacial rivers using the Google Earth Engine platform. The model is the first of its kind developed for the Himalayan region and uses multispectral S-2 satellite data to delineate submerged water channels, vegetated surfaces, and emerged, unvegetated sediment bars, and then to track their variations over time. The study focused on three training sites: Langtang-Khola (Nepal), Saltoro (Pakistan), and Nubra (Jammu and Kashmir) rivers, and one testing site, the Ganga-Bhagirathi River (India). A total of 900 polygons were used as training samples for the random forest classifier, which were further divided into 70% calibration and 30% validation datasets for the training sites, and a separate validation dataset was acquired from the testing site to assess the model performance. The model achieved high accuracy, with an average overall accuracy of 96% and a kappa index of 0.94, indicating the reliability of the S2 data for modeling proglacial geomorphic features in the Himalayan region. Therefore, this study provides a reliable tool to detect past and current morphological changes occurring in the Himalayan proglacial rivers, which will be of great value for both research and river management purposes.

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Section: Methodological Approach and Workflowmentioning

confidence: 99%

Supervised Geomorphic Mapping of Himalayan Rivers Based on Sentinel-2 Data

Mukhtar,

Bizzi,

Comiti

2023

Remote Sensing

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“…Approaches to predicting ood channel response include identi cation of stream power thresholds (Magilligan, 1992;Yochum et al, 2017), duration of ow above a critical value (Costa and O Connor, 1995), and downstream gradients in stream power (Gartner et al, 2015). However, other studies have found that hydraulic forces alone are not able to explain geomorphic impacts of oods (e.g., Heritage et al, 2004;Nardi and Rinaldi, 2015;Surian et al, 2016) and highlight the importance of other factors such as human obstructions (Langhammer, 2010); lateral con nement (Thompson and Croke, 2013; Sholtes et al, 2018;Ruiz-Villanueva et al, 2023); pre-ood channel planform (e.g., Surian et al, 2016) and channel bed particle packing geometry and stability (e.g., East et al, 2018;Masteller et al, 2019).…”

Section: Introductionmentioning

confidence: 99%

Landslide-channel feedbacks amplify channel widening during floods

Bennett,

Panici,

Rengers

et al. 2024

Preprint

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Channel widening is a major hazard during floods, particularly in confined mountainous catchments where roads and buildings compete for space with river channels. Flood-induced channel widening is also an important process in eroding and shaping the landscape. However, channel widening during floods is not well understood and not always explained by hydraulic variables alone, with implications for flood risk management. Floods in mountainous regions often coincide with landslides triggered by heavy rainfall on steep valley sides. Whilst the long-term impact of increased sediment supply on channel widening is well established, landslide-channel interactions at the event timescale are not well known or documented. Here we demonstrate with an example from the Great Colorado Flood in 2013, a 1000-yr precipitation event that induced a 200-yr flood, and 100-yrs of erosion, how landslide-channel feedbacks can substantially amplify channel widening and flood risk. We use a combination of field analysis and multiphase flow modeling to document landslide-channel interaction during the flood event in which sediment delivered by landslides temporarily dammed the channel before failing and bulking the flow with sediment resulting in large channel widening. We propose that such landslide-flood interactions will become increasingly important to account for in flood hazard assessment as flooding and landsliding increase with extreme rainfall under climate change.

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“…This study adopts a more integrated spatial approach to include both channel and floodplain morphological and sedimentological impacts and, in a new way for an actively meandering system, to assess the locations at which both sediment loss and accumulation occurred during a single flood season marked by unusually extreme river discharges. The remote sensing approach as used here combined several sources of data for detailed monitoring, and we are now able to provide specific evidence of what a single season can achieve, including three-dimensional analysis of the whole floodplain in contrast to studies that have focussed on planform or channel crosssectional geometry (Major et al, 2019;Ruiz-Villanueva et al, 2023).…”

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The heterogeneous geomorphological impact of an exceptional flood event and the role of floodplain vegetation

Dawson,

Lewin

2023

Earth Surf Processes Landf

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Application of an integrated spatial approach combining several sources of remote sensing data to include both channel and floodplain morphological and sedimentological impacts has identified the geomorphological effects of three extreme flood events during a single flood season (2019–2020) along a 16‐km reach of the River Teme, UK. This combined approach allowed the assessment of in‐channel pattern development, incision and aggradation; lateral bank migration; and overbank sedimentation and scour by out‐of‐channel flows. Rates of change during the event period were compared with those in the previous 10 years. The approach also allowed the role of vegetation and cultivation, both bankside and out on floodplains, to be assessed with variations in the extent of riparian wood and channel slope driving contrasts in the extent of the response. The spatial impacts from such extreme events are highly localised, varied in kind, and can be considered for both rivers and floodplains together. Erosional effects were distinctively distributed and not simply contributions to ongoing meander development; channel aggradation was localised, and overbank sedimentation explicably patchy. In reaches without woody vegetation, differences in channel and floodplain slope, local floodplain relief as created by prior events, and the impact of man‐made structures were factors that drove variations in flood response. This study strongly underlines the role of continuous riparian vegetation in maintaining bank stability and constraining lateral channel migration, but also to the potential influence of floodplain vegetation and planting for ‘natural engineering’ in the context of floodplains as well as channels in comparable environments. Maintenance of riparian vegetation in the context of landowner and Natural England conflict and management of future flood risk is important, but also highlighted is the need to consider the role of hedgerows and wider planting for constraining soil and riverbank erosion during flood events.

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River widening in mountain and foothill areas during floods: Insights from a meta-analysis of 51 European Rivers

Cited by 12 publications

References 80 publications

Supervised Geomorphic Mapping of Himalayan Rivers Based on Sentinel-2 Data

Supervised Geomorphic Mapping of Himalayan Rivers Based on Sentinel-2 Data

Landslide-channel feedbacks amplify channel widening during floods

The heterogeneous geomorphological impact of an exceptional flood event and the role of floodplain vegetation

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