Impacts of a large flood along a mountain river basin: unravelling the geomorphic response and large wood budget in the upper Emme River (Switzerland)

Virginia Ruiz-Villanueva, Alexandre Badoux, Dieter Rickenmann, Martin Böckli, Salome Schläfli, Nicolas Steeb, Markus Stoffel, Christian Rickli
2018 Earth Surface Dynamics Discussions  
<p><strong>Abstract.</strong> On July 24, 2014, an exceptionally large flood (recurrence interval ca. 150 years) caused large-scale inundations, severe overbank sedimentation and damage to infrastructures and buildings along the Emme river (central Switzerland). Widespread lateral bank erosion occurred along the river, thereby entraining sediment and large wood (LW) from alluvial forest stands. This work analyses the catchment response to the flood in terms of channel widening and LW
more » ... and deposition, but also identifies the factors controlling these processes. We found that hydraulic forces (e.g., stream power index) or geomorphic variables (e.g., channel width, gradient, valley confinement), if considered alone, are not sufficient to explain the flood response. Instead, spatial variability of channel widening was firstly driven by precipitation, and secondary by geomorphic variables (e.g., channel width, gradient, confinement and forest length). LW recruitment was mainly caused by channel widening (lateral bank erosion) and thus also controlled by precipitation. In contrast, LW deposition was controlled by channel morphology (mainly channel gradient and width). However, we also observed that extending the analysis to the whole upper catchment of the Emme river, including all the tributaries and not only to the most affected zones, resulted in a different set of significant explanatory or correlated variables. Our findings highlight the need to continue documenting and analysing channel response after floods at different locations and scales. Whereas this is key for a better process understanding, the identification of controlling factors can also contribute to the identification of critical reaches, which in turn is crucial for the forecasting and design of sound river basin management strategies.</p>
doi:10.5194/esurf-2018-44 fatcat:wgrdn46weravxh3jfkdpqcfnyy