GM4.13

Changes occurred in denudation/sedimentation processes (understood here as the transfer of solid materials from one place of the earth’s surface to another, by different agents) in the latter part of the Holocene, mainly the last couple of centuries, are examined, trying to estimate rates and assess the role of human and natural agents. Three issues are addressed here, on the basis of some case studies: slope movements and their contribution to denudation and relief evolution; “technological denudation” due to human activities; general evolution of sediment accumulation (consequence of denudation).

Analyses of materials transfer by, and frequency of, slope movements in N Spain have shown the importance of human influence already in Neolithic times, and more so after the Industrial Revolution. Significant increases have been observed since the middle of last century and slope movements seem to be in some cases the main factor of relief evolution.

Human activities related to urban-industrial development, infrastructure and mining activities represent an important “human geomorphic footprint” (expressed as volume of materials displaced or area occupied by new “anthropogeoforms”; yearly total or per capita). If the materials thus moved were evenly distributed over all emerged lands they could be presently equivalent to a >1 mm a^-1 (“technological”) denudation. As this is the consequence of growing population, technological and economic development, it will probably intensify with time.

Sedimentation rates directly determined (Pb-210, Cs-137) in a number of estuaries, lakes and reservoirs show in general a clear increase since early 20^th century, particularly after its middle. Compilation and analysis of sedimentation rates in a variety of sedimentation environments in different regions of the world, since late 19^th century, also show, with almost no exception, a similar trend. Comparison with rainfall evolution does not explain the changes observed. However, indicators of the intensity of human activity, especially GDP (Gross Domestic Product; total, not per capita; strongly related to our capacity to transform land), show a good similarity with sedimentation rates trends. This indicator also shows a close correlation with geomorphic disasters frequency (another manifestation of the general intensification of geomorphic processes).

On the basis of the information gathered and results presented, some tentative conclusions are proposed. It appears that presently humans are, by far, the main denudation agent. Direct and indirect transfer of rock, soil and sediment by human activities could be one order of magnitude greater than by natural agents. The rates of some geomorphic processes seem to have experienced a significant acceleration (about tenfold?) in less than a century, due to land surface transformation rather than to climate change. This “great geomorphic acceleration” represents a part of the “Great Acceleration” occurred after mid-twentieth century. Global geomorphic change (independent of climate change) should thus be considered as one of the characteristics of the Anthropocene, for which the end of World War II would indeed be an appropriate starting date.

How to cite: Cendrero, A., Remondo, J., and Forte, L.: Denudation, global change and the Anthropocene, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2320, https://doi.org/10.5194/egusphere-egu21-2320, 2021.

Vegetation is one of key factors controlling landslide occurrence, including frequency, size, and depth. Both horizontal and vertical root networks have important roles in stabilizing hillslopes. For instance, landslide density can be moderated by dense and deep tree root reinforcement below the potential soil slip surfaces. Landslide size can be reduced by extended dense and thick tree root networks, providing cohesive and lateral hillslope reinforcement. Vegetation conditions such as density and composition also alter the landslide occurrence because they are linked to root network density and strength, which are affected by different biogeoclimatic conditions. These findings regarding landslide-vegetation interactions were mostly based on rainfall-induced landslide cases. Preliminary, but yet to be confirmed, findings in Eastern Iburi Earthquake-Induced Landslides (EIL) showed that lateral root reinforcement might moderate the size of landslide scars in forested areas compared to logged areas.  Therefore, our primary objective was to examine the effect of different vegetation composition on EIL based on global data and supplemental analysis.

Our global database of EIL was compiled for a 20-yr period using a literature review and GIS analysis. Documented landslides were restricted to shallow mass movements with depths approximately less than 3 m. For vegetation-related analysis, we used Net Primary Production (NPP) and Leaf Area Index (LAI) derived from MODIS-Terra satellite images. Twenty-seven EIL cases were recorded in our database occurring from 2002 to 2018. Among these, 26% of the total cases occurred in Japan, followed by 18% for both in China and New Zealand. Based on climate types, 22% of total EIL cases occurred in temperate oceanic climate (Cfb) dominated by New Zealand EIL cases, and 15% cases occurred in humid subtropical climate region (Cfa), such as Japan. Moreover, 7% cases occurred in tropical rainforests (Af) and 7% cases in hot desserts climate regions (BWh). Among the 27 recorded cases of EIL, we selected eight EIL cases based on biomass classes, which are low (0-2 gC/m²/day), moderate (3-5 gC/m²/day), and high (>5 gC/m²/day). A power-law cumulative-area distribution of landslide areas showed that low biomass sites had the largest landslides (11,000 m²), followed by moderate biomass (3000 m²), and high biomass (200-3000 m²) with the smallest landslides, possibly associated with the density of vegetation. In low biomass regions, the average LAI was 1.8 m²/m², which was three times lower compared to regions with higher biomass. This indicates that in regions with sparse vegetation, slope reinforcement by dense lateral root networks was minimal. Future research is focusing on compiling information on landslide scars and root depth to assess the effects of vegetation density and vertical root reinforcement on landslide characteristics in each biomass class.

How to cite: Ritonga, R. P., Gomi, T., Sidle, R. C., Koyanagi, K., Arata, Y., and Noviandi, R.: Does Vegetation Really Affect Earthquake-Induced Landslides? Preliminary Analysis of Worldwide Database, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10551, https://doi.org/10.5194/egusphere-egu21-10551, 2021.

The Mazeri Valley in the Greater Caucasus (Georgia) is characterized by a highly dynamic landscape with several active mass-wasting processes. The spatial and temporal dynamics of these geomorphic processes have, over time, resulted in the formation of large cones and fans. In this context, the coupling between the hillslope and the channel plays a fundamental role in controlling the catchment sediment dynamics. The sediment produced at higher altitudes on hillslopes may occasionally reach the debris-flow channel network, and downstream propagation may have significant effects on the fluvial environment and create potential hazards for the resident population, tourists and infrastructures. In this study, we aim to better understand sediment fluxes in the mountain headwater stream in the Mazeri Valley. In this regard, a tree-ring-based chronology of the debris-flow activity on a large cone was created, to shed light on sediment connectivity and better understand the coupling between the main debris-flow channel and the bedload of Dolra river. The 161 disturbed trees sampled allowed to reconstruct a minimum of 12 significant debris-flow events over the last 65 years, with all of these events involving possible sediment input into the stream system of the Dolra river. These successional events, with a return interval of 5.4 years, have partially destabilized the fluvial system and locally induced a switch in the channel style to a braided channel. Although the cone studied is not directly located in a proglacial environment, its geomorphological dynamics remain highly dependent on water and sediment inputs from upstream, giving the presence of retreating glaciers and then paraglacial conditions at high altitude. The ongoing glacial retreat and increased climate variability will certainly lead to a massive output of sediments at high altitude, favoring an increase in geomorphic activity in the area. Many other fan and cone complexes are present in the Mazeri Valley, as well as in other adjacent valleys, and there are no documentations regarding their dynamics (e.g., typology, nature and source areas of hillslope processes, their coupling with channelized sediment-water flows, frequency–magnitude relationships). In this regard, we expect that the present pioneering study in this area will encourage more researches to investigate sediment fluxes for a better land use and preservation of water in Georgia under climate change.

Cette étude représente une contribution pour le projet « Impact du changement climatique sur les glaciers et les risques associés dans le Caucase Géorgien - IMPCLIM », financé par l’Agence Universitaire de la Francophonie (AUF) et le Ministère pour la Recherche et l'Innovation de Roumanie (MRI) à travers l'Institut Roumain de Physique Atomique (IFA).

How to cite: Pop, O., Germain, D., Gavrilǎ, I.-G., and Elizbarashvili, M.: Dendrogeomorphic reconstruction of debris-flow activity in Mazeri Valley, Greater Caucasus, Georgia, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12624, https://doi.org/10.5194/egusphere-egu21-12624, 2021.

Extensive road construction works were recently undertaken in the remote eastern part of the Peruvian Cordillera Blanca, aiming at better connecting isolated mountain communities with regional administrative centres. In the Río Lucma catchment, approximately 47 km of roads were constructed between 2015 and 2018, triggering several landslides that affected an approximate area of 32 ha. We identified and characterised these landslides by combining field mapping, visual interpretation and semi-automated analysis of satellite imagery (PlanetScope and RapidEye-2), and analysis of rainfall data from two stations of the Servicio Nacional de Meteorología e Hidrología del Perú (SENAMHI). We investigated in detail three specific areas of interest, where we identified, delineated, and described 56 landslides. We classified the landslides in relation to their position to the road as: landslides downslope the roads (48.2%), complex landslides crossing the roads (46.4 %), and landslides onto the road (5.3%). According to the type of movement, we found that the slide-type movement (60.7%) prevails over the flow-type movement (39.3%). Timewise, we found that 75% of landslides were observed on satellite imagery simultaneously with road construction work, while the remaining 25% were identified between one week and seven months after the roads had been constructed. We analysed lagged cumulative rainfall data against the occurrence of these subsequent landslides, determining that a two-week rainfall accumulation can act as triggering factor of landslides after road construction work. In general, 51% of the landslides were observed during the wet season (November to April) while 41.1% occurred during El Niño–Southern Oscillation (ENSO) strong cool phase or “La Niña” period. We observed that the majority of mapped landslides were directly (e.g., landslides resulting from slope undercutting) or indirectly associated with road constructions (e.g., rainfall-induced landslides resulting from a combination of extreme precipitation over slopes with decreased stability) and that the road constructions also may set preconditions for subsequent rainfall-triggered landslides.

How to cite: Abad, L., Hölbling, D., and Emmer, A.: Road Construction and Rainfall as Landslide Triggers in the Rio Lucma Catchment, Eastern Cordillera Blanca, Peru, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11015, https://doi.org/10.5194/egusphere-egu21-11015, 2021.

Background: In the late 20^th century great advancement was made in the field of hiking trail studies. The main concerns for these trails are susceptibility to soil erosion and dynamic landform changes in their nearest area. The impacts of the trails for vegetation were also studied with trampling and soil exposure being the most destructive. Today, With the higher and higher resolution for digital terrain models being available and advanced simulation algorithms and computing, it is possible to perform advanced modeling of a hillslope runoff.

The aim: The aim of these studies is to determine the impact of hiking trails on hillslope water runoff by comparison of the water discharge values during simulated precipitation events.

Method: The comparison is made possible, with the use of digital terrain modeling to create hillslope with and without a hiking trail, in its pre-erosion state. Both models then are subject to Simulated Water Erosion (SiMWE) based on the Monte Carlo simulation method. The algorithm is implemented in an open-source GRASS GIS program in the form of r.sim.water and r.sim.sediment modules. Exemplary hillslopes also present different scenarios based on the trail to slope alignment angle (0° - 22°; 22,1° - 45°; 45,1° - 67° and 67,1° - 90°). 

During the session a case study area of a suburban mountain range within Kielce city (Poland) will be introduced, together with the results of simulation values and their spatial distribution for the exemplary hillslopes. With it, the role of the hiking trail and its environmental impact on water runoff will be better understood and easier to predict.

How to cite: Kopyść, P.: Does the trail matters? - In search of the environmental impact of hiking trails on the hillslope runoff., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-118, https://doi.org/10.5194/egusphere-egu21-118, 2021.

Sediment flux in cold environments is a crucial proxy to link glacial, periglacial, and fluvial systems and highly relevant to hydropower operation, water quality, and the riverine carbon cycle. However, the long-term impacts of climate change and multiple human activities on sediment flux changes in cold environments remain insufficiently investigated due to the lack of monitoring and the complexity of the sediment cascade. Here we examine the multi-decadal changes in the in-situ observed fluvial sediment fluxes from two types of basins, namely, pristine basins and disturbed basins, in the Tibetan Plateau and its margins. The results show that the fluvial sediment fluxes in the pristine Tuotuohe headwater have substantially increased over the past three decades (i.e., a net increase of 135% from 1985–1997 to 1998–2017) due to the warming and wetting climate. We also quantify the relative impacts of air temperature and precipitation on the increases in the sediment fluxes with a novel attribution approach and finds that climate warming and intensified glacier-snow-permafrost melting is the primary cause of the increased sediment fluxes in the pristine cold environment (Tuotuohe headwater), with precipitation increase and its associated pluvial processes being the secondary driver. By contrast, the sediment fluxes in the downstream disturbed Jinsha River (southeastern margin of the Tibetan Plateau) exhibit a net increase of 42% from 1966-1984 to 1985-2010 mainly due to human activities such as deforestation and mineral extraction (contribution of 82%) and secondly because of climate change (contribution of 18%). Then the sediment fluxes dropped by 76% during the period of 2011-2015 because of the operations of six cascade reservoirs since 2010. In an expected warming and wetting climate for the region, we predict that the sediment fluxes in the pristine headwaters of the Tibetan Plateau will continue to increase throughout the 21st century, but the rising sediment fluxes from the Tibetan Plateau would be mostly trapped in its marginal reservoirs.

Overall, this work has provided the sedimentary evidence of modern climate change through robust observational sediment flux data over multiple decades. It demonstrates that sediment fluxes in pristine cold environments are more sensitive to air temperature and thermal-driven geomorphic processes than to precipitation and pluvial-driven processes. It also provides a guide to assess the relative impacts of human activities and climate change on fluvial sediment flux changes and has significant implications for water resources stakeholders to better design and manage the hydropower dams in a changing climate. Such findings may also have implications for other cold environments such as the Arctic, Antarctic, and other high mountainous basins.

Furthermore, this research is under the project of "Water and Sediment Fluxes Response to Climate Change in the Headwater Rivers of Asian Highlands" (supported by the IPCC and the Cuomo Foundation) and the project of "Sediment Load Responses to Climate Change in High Mountain Asia" (supported by the Ministry of Education of Singapore). Part of the results are also published in Li et al., 2018 Geomorphology, Li et al., 2020 Geophysical Research Letters, and Li et al., 2021 Water Resources Research.

How to cite: Li, D., Lu, X., and Zhang, T.: Fluvial sediment fluxes response to modern climate change and human activities in the Tibetan Plateau and its margins, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-130, https://doi.org/10.5194/egusphere-egu21-130, 2021.

Mountain basins can be affected by Large Infrequent Disturbances (LIDs) that have the power of changing their forest cover and morphological settings, and supplying high amounts of sediments to river networks. The resulting cascading processes are often underestimated although their understanding would improve river management strategies. The recent improvements in the field of sediment transport monitoring and analysis allow to gather a deeper understanding of these long-lasting and complex chains of processes, especially in mountain streams. This contribution aims at investigating the suspended sediment transport exhibited by two recent (summer-autumn 2020) over-bankfull (> 2.3 m³/s) flood events occurred in the Rio Cordon, an alpine basin (5 km²) strongly altered by the Vaia storm (October 2018). This LID blew down 139 trees along the main active channel that were removed by local forest operations after the event, leaving exposed banks and increasing the availability of fine sediment. Two water quality sondes were placed upstream and downstream the windthrow affected area (WAA) to monitor the Suspended Sediment Load (SSL) and quantify the contribution of the WAA in supplying sediments. Water discharge and suspended sediment transport were continuously measured by the two instrumentations, while water samples and direct discharge measurements (salt dilution method) were taken to derive rating curves and calibrate the turbidity meters. Results show that the early September 2020 event (Q_max=2.67 m³/s) produced a SSL = 39.27 t and a SSL increase of +5% between the downstream and upstream cross-section. To this, it was also registered a +44% variation of SS maximum concentration (SSC g/l) which can be ascribed to the contribution of the WWA. The event of October 2020 (Q_max=3.05 m³/s) instead, registered a SSL of 179.22 t and a SSL and SSC_max variation of +334% and +81%, respectively. The preliminary results suggest that the SS is not related to the water discharge but for this reason, further analysis and data collection will be made, also considering rainfall data. However, the ongoing monitoring of this area represents a suitable and promising approach for understanding the cascading processes on the SS dynamics in a mountain basin affected by a LID.

How to cite: Pellegrini, G., Rainato, R., Martini, L., Mao, L., and Picco, L.: Cascading processes of the Vaia storm in the italian Rio Cordon mountain catchment, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5397, https://doi.org/10.5194/egusphere-egu21-5397, 2021.

Dynamics of bedload transport increases with an increase of hydrologic parameters, i.e. stream power, water velocity and discharge. In mountain stream channels, these parameters increase in the downstream direction, and therefore the dynamics of bedload transport increase down the channel. This pattern may become altered temporarily or over long periods of time due to local extreme events or human impact. Here, we identify disturbances in bedload transport in the formerly glaciated catchment located in the Western Tatras in Poland. We then determine the role of disturbances in system connectivity and sediment transfer. Bedload transport measurements in the Chochołowski catchment were performed in the period 1975 to 2018. The said process occurred as many as triggered up to several times a year. However bedload became activated along the entire length of the channel system (10.5 km) every 2 to 5 years when the stream discharge exceeded 10 m³ s^-1. The distance of bedload movement during such events was between 12 m in headwaters and over 100 m in the lower reach. In such situations, bedload dynamics increased downstream, and stream power was sufficient to overcome local barriers (i.e. boulder and log steps). Downstream increases in bedload dynamics was disturbed and inverted by sudden snowmelt and locally heavy rainfall. These types of events caused the dynamics of bedload transport to be up to 320% greater in the upper part of the studied catchment and to decline in the downstream direction over a distance of 7 km to yield an attenuation effect. The same pattern was observed in local tributaries where the dynamics of bedload transport were 200% higher in the upper part and attenuation was observed along a distance of 1.5 km in the downstream direction. All events of this type cause seasonal disturbances in bedload transport. However, the greatest effect on bedload dynamics was produced by natural deforestation. A 16% decrease in forest cover causes a fluvial system disequilibrium manifested in an intensification of hydro-geomorphologic processes and formation of new landforms.

How to cite: Płaczkowska, E., Krzemień, K., Gorczyca, E., Bojarczuk, A., and Żelazny, M.: Disturbances in coarse bedload transport in a formerly glaciated catchment, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1201, https://doi.org/10.5194/egusphere-egu21-1201, 2021.

Knowledge of sediment production mechanisms and their potential controlling factors contributes to our understanding of geomorphological processes. Previous studies highlighted the link between sediment yield and anthropogenic (e.g. agricultural practices) and natural factors (e.g. climate, topography, river runoff, lithology and vegetation cover). The rugged western slopes of the Peruvian Andes shows different climate regimes with arid climates and desertic vegetation in the south and tropical climates and abundant vegetation in the north. In this region, agricultural and water regulation projects are concentrated.

However, the number of studies on sediment yield and its controlling factors are limited along the Peruvian Andes. Most studies on the western slopes have focused on the Northern part of Peru and showed a 3 to 60 times increase of sediment yield during El Niño (ENSO) events compared to normal years. The storm events rapidly mobilized sediment that was accumulated in the mountain and piedmont areas during dry normal years. In the central part of Peru where the main reservoirs, irrigation systems, and water supply plants are located, few studies were realized. They concluded that the relation between sediment production and both environmental and anthropogenic controlling factors needs to be further explored.

In this study, we identify the spatial patterns of sediment yield along the western slopes of the Peruvian Andes and analyze the main environmental controlling factors. Our study presents data on sediment yield of 20 catchments. The data contains information on suspended sediment load from gauging stations, reservoir sedimentation and water turbidity. We used satellite-based data to derive topographic information (SRTM v.3 DEM by NASA), daily precipitation covering the period 1981 to 2016 (PISCO product by Senamhi), daily discharge covering 1970 to 2020 (GloFAS-ERA5 global river dataset), lithological strength (global lithological map GLiM), and vegetative cover (MODIS Land cover type product). Our first results show a significant influence of the lithology, maximum discharge and topographic relief on sediment yield. The results of the analyses for the Peruvian Andes will be compared with previous studies in the Northern and Southern Andes.  

How to cite: Rosas, M. A., Vanacker, V., Clapuyt, F., and Viveen, W.: Spatial variation in sediment fluxes along the western slopes of the Peruvian Andes, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10041, https://doi.org/10.5194/egusphere-egu21-10041, 2021.

Bhutan, being a Himalayan mountain country, extends ca. 305 km from west to east and 145 km from south to north, covering an area of 47,000 km². Bhutanese Himalaya mountains are divided into three latitudinal belts from south to north: the sub-Himalayas or Himalayan foothills (up to 1,500 m in altitude), the inner Himalayas or middle ranges with flat valleys (from 1,500 to 4,500 m), and the Great Himalayas of high mountains (about 4 500 m). The Black Mountain Range, stretching longitudinally, divides this country into the eastern and western parts. The belt system of landforms is closely related to the geological structure. In the north, metamorphic and crystalline rocks (mainly gneisses and granites) dominate, while in the south there are sedimentary rocks associated with the molasse-like sediments in the Siwalik range. The distribution of precipitation from approx. 500 mm in the north to 5000 mm in the south of the country relates to this geological and morphological belt system. The main rivers flow longitudinally and have perpendicular tributaries. The digital elevation model of Bhutan was analysed geomorphometrically and, on this basis, places with high potential mechanical denudation were identified. The most evident manifestation of this denudation are numerous landslides occurring on the valley slopes. These landslides, especially in the monsoons period, deliver enormous amounts of landslide material to the valley bottoms, and most often directly to the river channels. The landslide material in the form of fluvial material is further transported along the rivers and deposited in the foreland of the Himalayas. After the summer monsoon period, water samples were collected in selected rivers. The collected water samples were subjected to hydrochemical analyzes. The studied river waters in the middle part of the country are characterized by low mineralization. The obtained results allow for a preliminary characterization of the spatial diversification of the denudation potential of Bhutan's river waters. Referring to the physiographic division of Bhutan, it can be confirmed that the middle zones, meridional ridges and valleys of this country are characterized by low chemical denudation and high mechanical denudation, while the southern tips of the country Front Hills and Piedmont are dominated by accumulation processes due to a significant reduction in river gradient.

How to cite: Mazurek, M., Zwoliński, Z., and Niedzielski, P.: Spatial distribution of denudation processes in Bhutan, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16058, https://doi.org/10.5194/egusphere-egu21-16058, 2021.

The recent increase in frequency and extent of severe wildfires in South-Central Chile is degrading the already eroded soils of the Coastal Cordillera. Spatially explicit quantification of erosion triggered by that disturbances may reveal useful information for soil conservation and land planning purposes, which is especially relevant in drinking-water catchments. We compared estimations of water erosion using a process-based and an empirical modeling approaches in a small (173 ha) burned drinking water catchment. To this end, we implemented the GeoWEPP process-based model and the RUSLE empirical approach for different scenarios of wildfire severity using remote sensing, in situ soil and hydro-meteorological data (2001-2019). Individual Hydrologic Response Units resulted in very low erosion rates in GeoWEPP respect to RUSLE, while both simulations represent low erosion rates respect to observations reported for other latitudes of the Coastal Cordillera. Those low erosion rates could be explained by low rainfall erosivity and high critical shear stress, which in turn is a consequence of soil compaction.  The spatial variations of the modeled sediment yields (2001-2019) were associated both to the wildfire and to the land management at hillslopes, which involves clear cut timber harvest at most forest plantations areas. A better quantification of those erosion processes is necessary to improve the understanding of the evolution of Chilean forestry landscape, in order to prioritize efforts for soil conservation and ecosystem restoration.

How to cite: Tolorza, V., Poblete, D., González, V. I., Zambrano-Bigiarini, M., Cabezas, J., and Galleguillos, M.: Fire-induced catchment erosion on a depleted soil system from GeoWEPP and RUSLE models, Santa Olga, Chile, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13140, https://doi.org/10.5194/egusphere-egu21-13140, 2021.

Soil erosion and sediment delivery to rivers are important drivers for land degradation and environmental change in mountain agroecosystems.  These factors are especially severe in areas affected by intermittent heavy rainfalls after dry periods, and human practices such as deforestation or clearcutting practices. Many Mediterranean mountain environments underwent conversion of rangelands into croplands during the previous centuries increasing the risk of erosion. After land abandonment the process was gradually reversed during the middle of the 20^thcentury, allowing the recovery of natural land cover and reduced soil erosion rates. To further control the high erosion rates, several afforestation programs introduced pine forests at the headwater of most Mediterranean mountain catchments transforming the landscape by terracing and reducing the sediment connectivity. However, nowadays, forests’ different management could lead to high erosion rates and subsequent landscape modifications. To understand the possible effect of these practices together with the current agricultural management, we have combined the strength of empirical data and spatially distributed modelling. Surface soil samples from different land uses were collected in a representative catchment at the foot of Santo Domingo range at the border of the central Ebro River valley. The study catchment was mostly cultivated at the beginning of the 19_th century but changed to rangeland and pine afforestation in the last 50 years. The remaining croplands are predominated by rainfed agriculture that leaves soils mostly unprotected from June to January when erosive storms occur. The main land uses are croplands, pine afforestation, scrubland and Mediterranean forest.

In this study, we propose an ensemble technique composed of ¹³⁷Cs derived soil redistribution rates as specific point values and as a calibration tool for the widely used WaTEM/SEDEM sediment delivery model. Thus, by the use of ground truth and modelled data we aim to i) apply the WaTEM/SEDEM model at the catchment scale and calibrate it with ¹³⁷Cs derived soil redistribution rates for finding an optimal set of input parameters; ii) examine the effect of clearcutting and agricultural practices on the total erosion; iii) compare the modelled results with recently calculated sediment apportionments by using the sediment fingerprinting technique.

Our findings highlight the use of spatially distributed models combined with ¹³⁷Cs derived rates as a powerful tool to understand the driving factors of soil erosion in the last decades and to delineate the hotspot areas that could suffer high erosion if subjected to certain management practices.

How to cite: Lizaga, I., Gaspar, L., Latorre, B., and Navas, A.: Disentangling the effect of past and present agroforestry practices in modifying landscapes of Mediterranean mountains, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3312, https://doi.org/10.5194/egusphere-egu21-3312, 2021.

Landslide dams occur when a landslide deposits in the riverbed and stop the river flow, creating lakes. They act as big sediments traps that modify the sediment flux in the whole catchment. By changing the sediment load, the dams change the erosion rates upstream and downstream. Although most landslide-dammed lakes are ephemeral, some stay in place and disappear only when they have been filled with sediments. We study the Hintersee lake in the Berchtesgadener Land, Germany, and aim to determine the sediment budget of the infilled lake and the dam duration before breaching. This landslide dam formed 3520 years BP from a rockslide of 15-18 x 10⁶ m³. We propose to reproduce the formation of the Hintersee landslide dam and its infilling using different scenarios. We first use a 1 m resolution digital elevation model to rebuild the valley floor before the rockslide event, three different rockslide source areas and the landslide dam shape before fluvial incision. We apply the Gerris shallow water flow solver to simulate the landslide runout and to recreate the landslide dam deposition characteristics from the different source topographies and several Voellmy rheologies. We choose the best-fitting scenario to assess a sediment budget of the Hintersee landslide-dammed lake.

How to cite: Hauthaler, T., Argentin, A.-L., Robl, J., Prasicek, G., Hölbling, D., Hergarten, S., Abad, L., and Dabiri, Z.: Landslide dams acting as sediment traps: Example of the lake Hintersee, Berchtesgadener Land, south-eastern Germany, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12149, https://doi.org/10.5194/egusphere-egu21-12149, 2021.

The storm Gloria was an exceptional episode of east storm occurred in the north and east of Spain from Sunday 19^th to Thursday 23^rd of January 2020. The impact was especially strong in the Mediterranean coast, causing the overflow of some rivers, abundant slope movements, cuts in the road and rail network, isolation of populations, and huge damage on the coastline.  It was classified as historical, not only because of the multiplicity of phenomena (wind, rain, snow, and waves) that happened simultaneously, but also because of the extension, affecting the entire Catalan territory. In order to have an overview of the effects of the storm in Catalonia, the Institut Cartogràfic i Geològic of Catalonia has carried out a quick response report (González et. Al., 2020), which has consisted of an inventory of the geomorphological impact and its consequences. The work carried out includes the production of post-event orthoimages of the coastal strip and some fluvial courses, a post-event field survey during the days immediately after, and a compilation of the information published in the media between 01/20/2020 and 02/18/2020. Also, a data collection campaign through online forms sent by email has been carried out, which provides more information of the sea gale effects, and validates and complete the preliminary inventory of slope movements. Thus, an inventory of slope movements has been obtained with a total of 352 documented landslides throughout the Catalan territory. In addition, a geomorphological mapping with the changes associated to river dynamics has been carried out, in two of the most affected sectors in NE Catalonia: the lower section of the Tordera river and the lower section of Ter river. This 1: 5 000 scale cartography, identify geomorphological elements from fluvial dynamics (active fluvial channels during the flood, active flood plain, erosion scarps of river banks, flow direction lines) and from coastal dynamics (washoverfans, coastal erosion and new creation stream-mouth bars). Finally, based on the analysis of the data collected, an estimate has been made of the impact that the storm Gloria has had on the territory, and how it has affected the different municipalities, in terms of damages and economic losses. The results of this quick response report allow (i) to have a geomorphological record of the storm extent in the short term, (ii) to provide basic information for the management and recovery of river areas, and (iii) to propose new strategies for geological risk management, among others.

How to cite: González, M., Micheo, M. J., Pinyol, J., Carles, M. R., Pi, E., Vila, M., and Roca, A.: The effects of the storm Gloria in Catalonia: The value of quick-response geological inventories as a tool for risk management, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2499, https://doi.org/10.5194/egusphere-egu21-2499, 2021.