GM1.1

Landslides are prevalent in mountain landscapes and interact with the river network in a myriad of ways with impacts on flood and debris flow hazards and landscape evolution. Floods in mountainous regions often coincide with a high density of landslides triggered by heavy rainfall. However, the impacts of landslide-delivered sediment on flood dynamics are not typically considered in flood hazard assessment. Higher up in the river network, landslide sediment supply is a key component of debris flows. Yet, assessments of climate change impacts on debris flows to date have focused on likely changes in rainfall triggering potential of debris flows, overlooking the role of landslide sediment supply.

In a first case study, I demonstrate with an example from the Colorado Front Range how landslide-channel feedbacks can significantly amplify channel erosion and flood risk. We used a combination of field analysis and modelling with a multiphase flow model R.avaflow to test the hypotheses that landslide-flood interactions amplified channel erosion during a major flood event in 2013 by (1) bulking of the flow and (2) dam formation and failure dynamics.

In a second case study, I demonstrate with an example from the Swiss Alps, how landslide sediment supply limits debris flow hazard in a warming climate. We forced the sediment cascade model, SedCas, with climate simulations to disentangle the interactions between hydrological triggering, landslide sediment supply and elevation on mountain basin sediment transfer and debris flow hazard over the 21^st century. 

How to cite: Bennett, G.: Accounting for landslide-channel interactions in landscape evolution and hazards, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4290, https://doi.org/10.5194/egusphere-egu22-4290, 2022.

Hard engineering solutions are becoming economically unviable due to the high costs of construction, maintenance and adaptation to changes in sea level and storms. ‘Engineering with Nature’ (including the creation of salt marshes, seagrass beds) offers a more economically viable alternative for coastal protection.

However, despite the growing recognition of the necessity to move towards this greener alternative for coastal protection, there are still large uncertainties about factors determining the resilience of these systems to environmental change. As a consequence of sea-level rise, and of the increased occurrence of extreme weather conditions, coastal habitats are at risk of degradation and possible recession.  Human interactions add a layer of complexity to natural processes. Among the others, the sediment delivery to coastal areas has significantly changed over the years, for instance due to changes in catchment management, with consequences for the resilience of coastal systems.

This work uses numerical models to investigate the morphological and hydrodynamic features of coastal systems with environmental change. These numerical tools consist of hydrodynamic models coupled with morphological and sediment transport modules. Results investigate feedbacks between the shape of existing shorelines, wetlands resilience and external forcing such as tidal currents and wind waves. Results provide information useful for the study and management of ‘Engineering with Nature’ interventions and highlights the importance of a whole-system approach for the correct management of coastal areas.

How to cite: Leonardi, N.: Coastal wetlands and seagrass dynamics with environmental change, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2798, https://doi.org/10.5194/egusphere-egu22-2798, 2022.