ID58: SedInOut: Sediment availability assessment linked to climate change

Abstract ID 250 | Date: 2022-09-12 17:47 – 17:49 | Type: Poster Presentation | Place: SOWI – Garden |

Schlögl, Matthias (1,2); Heiser, Micha (1); Fuchs, Sven (1); Spangl, Bernhard (1); Zimmermann, Markus (3); Rickenmann, Dieter (4); Scheidl, Christian Norbert (1)

In mountainous regions, natural hazards are omnipresent. Especially torrential processes such as debris flows frequently endanger populated areas and infrastructure facilities. In order to assess the impact of future changes related to the possible triggering of such mass flows, knowledge about the frequency is important. In this study, we analysed time series of more than 1,000 debris flow events based on a comprehensive event catalogue covering significant parts of the Eastern European Alps, supplemented by data available in the literature. Our study revealed three different approaches to characterise the frequency of debris flows: (i) irregular, (ii) regular, and (iii) clustered repose times. By applying a modified dynamic threshold concept in relation to debris flow triggering, we showed that in the case of irregular repose times, events can be assumed to occur randomly. However, our results indicated that for regular and clustered repose time series, interdependency between events is important and leads to dynamic changes in critical thresholds regarding climatic triggers and sediment availability. In case of regular and clustered repose types, modelling debris flow event frequencies will thus either result in an overestimation and underestimation of the occurrence probability of an event, respectively. Consequently, these biased estimates entail potentially substantial implications for mitigation and adaptation as well as risk management. In such a case, changes in climatic trigger conditions might not be independent of the prevailing geomorphological disposition i.e., sediment availability and land-use management activities.

Abstract ID 899 | Date: 2022-09-12 17:49 – 17:51 | Type: Poster Presentation | Place: SOWI – Garden |

Cantalejo, Marina; Millares, Agustín; Cobos, Manuel; Baquerizo, Asunción

The IPCC have declared Mediterranean regions as ‘hotspots’, due the severe consequences expected from climate change projections. Besides, high mountains basins in these environments, are highly required to be studied as observatories of hydrological changes and their associated impacts. The Guadalfeo’s river basin, (southern, Spain) is characterized by the influence of snow dynamics on fluvial regime and by the presence of hydraulic infrastructures with important regulating effects downstream. The sensitive hydrological response to changes on meteorological forcings shown in these areas, pointed to scenarios with low-to-no snow contributions, which will have important repercussion downstream such as on the availability of water resources or regulating floods. This work proposed to analyze the effect of climate changes scenarios from Coupled Model Intercomparison Project 5 (CMIP5), on Rules dam’s regulation strategies, situated downstream the headwaters of Guadalfeo’s river basin. Climate projections are first statistical downscaled to remove systematic modelled biases and attend the local inter-annual observed variability. The post-process projections of precipitation and temperature were subsequently used as inputs for physically based and distributed model which reproduce the spatial and temporal variability of the forcing agents and processes. that are particularly relevant in mountainous semiarid environments. This model was configured and calibrated for Mediterranean mountain areas and specifically for nival dynamics and hillslope sediment generation and transport after up to twenty years of monitoring works in the study site. Besides, the information related to soil loss enables to considerate the reservoir retention of sediment in future scenarios and the consequences on water storage capacity and flood risk assessment. To evaluate the implication on reservoir management in future scenarios, it is characterized by the water discharge since the dam started to operate in 2004, considering multiple factors (time of the year, level of water storage, ecological flow…) in the decision process. Under this actual dam’s operative characterization, it was analyzed the repercussions on water demand supply and the regulation capacity of extreme events. The results point to a reduction expected in the availability of water for the end of this century, linked to the predicted reduction of snowmelt resources and the loss of volume due to sedimentation processes. Furthermore, the probability of exceed the threshold for attenuate flooding downstream increase considerably. These results highlight the need to urgently implement adaptation and mitigation strategies in the headwater and high mountain basin. This work is part of Smart EcoMountains, the Thematic Center on Mountain Ecosystems of LifeWatch-ERIC.

Abstract ID 898 | Date: 2022-09-12 17:51 – 17:53 | Type: Poster Presentation | Place: SOWI – Garden |

Millares, Agustín (1); Eekhout, Joris (2); Cantalejo, Marina (1); Conesa, Carmelo (3); Moreno, Ricardo (4)

Understanding erosion, transport and sediment dynamics in high mountain catchments is essential to ensure effective conservation strategies. In Mediterranean high-mountain environments, the diversity of hydro-meteorological drivers, the torrential nature, the high topographic gradients, and the quick response of snow dynamics condition significant sediment transport rates. However, the relationship of erosion and transport processes between hillslopes and the fluvial network is poorly understood. The emerging topic of sediment connectivity offers the opportunity to study erosion and sedimentation processes holistically, with the potential to increase system understanding and improving catchment management. This work analyzes the processes that control sediment connectivity, and its associated transport processes, in several high-mountain watersheds of Sierra Nevada (southern Spain). For this purpose, 18 years of monitoring works of hydro-meteorological drivers, hillslope erosion processes, and bedload and suspended loads sediment transport along the fluvial network have been used to assess sediment connectivity. Besides, long-term assessment and spatial approaches were used by physical-based and distributed hydrological modeling, with a model designed, calibrated, and validated in the study area, specially configured to evaluate snow dynamics and erosive processes in Mediterranean mountainous environments. In addition, the current situation was contrasted with different future climate scenarios, which were adapted and implemented from European reference databases. The simulation results show how changes in the frequency and amount of snowfall affect hillslope erosion processes associated with raindrop impact and rill erosion. These changes alter downstream sediment connectivity patterns and their relationship between hillslope and fluvial systems, where downstream sediment connectivity increases along the rivers due to an increase of torrential events. These results also highlight the large variability between regional climate models used in this study and their relatively low spatial resolution with respect to the complex topographies of the study areas. The proposed methods and results of this research highlight the great sensitivity of both hydrological and erosive responses of high mountain environments to climate change and provide clues as to where and how best to plan adaptation and mitigation strategies. This work is part of Smart EcoMountains, the Thematic Center on Mountain Ecosystems of LifeWatch-ERIC.

Abstract ID 100 | Date: 2022-09-12 17:53 – 17:55 | Type: Poster Presentation | Place: SOWI – Garden |

Mair, Volkmar (1); Brardinoni, Francesco (2); Minotti, Federica (2); Rabanser, Monika (1)

Mass wasting is a threat to residential areas and infrastructure, causing widespread destabilsation in alpine stream channels, while being in relation with ongoing climatic changes. Although hillslope sediment supply represents a critical factor for stream channel stability during heavy rainfalls, there is a substantial lack of procedures for quantifying sediment availability and composition. Moreover, there is a general absence of validated empirical models for estimating hillslope sediment flux to the drainage network as a function of meteorological forcing. SedInOut, through a joint interregional effort, aims to develop methodologies for the quantification and characterization of hillslope sediment, while targeting for a sustainable land management that values geo-risk mitigation and sediment recycling.

Abstract ID 765 | Date: 2022-09-12 17:55 – 17:57 | Type: Poster Presentation | Place: SOWI – Garden |

Delaney, Ian Arburua (1); Anderson, Leif S. (1,2); Herman, Frederic (1)

Glaciers expel sediment, in addition to ice and water. The quantity of sediment depends on the subglacial hydrological conditions, as well as the bedrock erosion rate. As a result, changing glacier dynamics and melt will cause changes to glacier erosion and sediment discharge, which can impact the landscape surrounding retreating glaciers, as well as communities and ecosystems downstream. Thus, there lies an imperative to understand these systems. Due to the difficulties in observing subglacial erosional processes, numerical models provide a valuable means to understand sediment transport and erosion process below glaciers. In turn, insights into these processes can be used to better evaluate landscape changes in alpine regions as climate warms

Here, we present a numerical model to demonstrate the ways in which spatial heterogeneities in subglacial water velocity and sediment availability impacts sediment discharge and bedrock erosion below glaciers. This model operates by evolving a subglacial till layer in response to sediment transport conditions and sediment availability over hourly to decadal time scales.

Numerical experiments with synthetic test cases show the potential role of sediment availability and the heterogeneity of sediment transport across a glacier’s bed. When compared to field data, the model captures measured sediment discharge volumes from the Griesgletscher in the Swiss Alps. A parameter search shows that sediment grain size is a key control on the discharge of sediment due to the role it plays in mobilizing sediment from distal areas of the glacier bed, outside of main channels. Additionally, the model is applied to understand differential erosion patterns on debris-covered glaciers.

We hope that processes identified in the modelling framework can be used to guide field studies and data collection. Future model development includes integrating hillslope and other periglacial processes into the framework. Additionally, the modelling framework is available for use by other researchers to evaluate subglacial erosion and sediment transport processes.

Abstract ID 420 | Date: 2022-09-12 17:57 – 17:59 | Type: Poster Presentation | Place: SOWI – Garden |

Andrecs, Peter; Plörer, Matthias; Hagen, Karl

Climate change may affect natural hazards in many ways such as through changing seasonal precipitation distribution or increasing frequency and magnitude of heavy rainfall events; however, all these changes are subject to uncertainty. What is beyond doubt, however, is that mean air temperatures are increasing. Therefore, we developed a tool that allows to quantify sediment availability in direct relation to increasing temperatures.

Factors, which are directly related to the potential effects of rising air temperatures on hillslides include:

• The upward shift of the mountain permafrost boundary, i.e., the altitude above which the ground is continuously frozen, and, therefore, permafrost degradation.
• Changes to the forest cover, for example, due to altered water balance, bark beetle outbreaks, wildfire or windthrow, and the associated reduction in the protective effect of the forest.

In this contribution we focus on permafrost degradation. The rise of the permafrost altitudinal boundary is strongly related to the rise of the average annual air temperature (about 150 m/ °C). The loss of permafrost may cause instabilities of rocks or loose material layers, resulting in a rising hazard potential for hillslides. Infrastructure in ski resorts, but also transport infrastructure and settlements at lower elevations could be affected.

In the project RECIPE (Reinforcing civil protection capabilities into multi-hazard risk assessment under climate change) we developed an approach to realize the assessment of the future hazard potential for hillslides based on available information regarding permafrost shifts. General steps are:

1)     Determining the assumed shift of the permafrost boundary according to the increase in air temperature (IPCC scenarios)

2)     Determination of unstable areas caused by permafrost degradation by merging a DEM with the Alpine Permafrost Index Map (APIM), which was generated for the entire Alpine region within the project PermaNET, showing the probability of the presence of permafrost. The high spatial resolution of the APIM (approx. 30 m) allows applications at the local level.

3)     Determination of new release areas and process paths with runout-models

Conclusion

The approach was tested for examples in high alpine regions in Tyrol, Austria. Due to the temperature-induced upward shift of the permafrost boundary, high mountain areas above the current permafrost boundary will become increasingly unstable and thus contribute to more bedload and hillslide mass potential. A mass flow simulation from the additional release areas showed that significantly more infrastructure was affected by gravitational mass movements than in a simulation without considering the shift of the permafrost boundary.