GM4.1

On the northern slopes of Meseta Belgrano (MB), eastern foothills of Patagonian Andes in Argentina, complex of multiple overlapping rock avalanches and landslides can be found. Interpretation of remote-sensing data, field mapping, together with OSL dating of lacustrine sediments revealed that slope collapses evolved during last oscillations of the Patagonian Ice Sheet and after its retreat. The longest rock avalanche with ~11 km runout originated most likely before the last glacial advance following the LGM because it involves moraine deposits in part of the scarp area. We suppose, that the distal part of the rock avalanche body was subaqueous due to presence of a proglacial lake in Lago Pueyrredón Valley after LGM. The hummocky character of the distal body and its lithological composition coming from MB bedrock was preserved, but the deposit is discontinuous with straight east-west glacial lineations on the surface. We think this is result of erosion by the ice sheet approaching from East during post-LGM glacial fluctuations. Next pronounced landslide activity took place after ~17 ka BP, when at least three rock avalanches overlaid lacustrine sediments in a dropping proglacial lake. One of them, superimposing the above described older rock avalanche, evolved from the collapsed moraine deposit and created ~5 km long lobe with subaqueous radial distal part. In the proximal parts of the rock avalanches east from this form, bellow the slopes of MB, distinct large ridge-like forms are visible in topography. They are similar to moraine ridges preserved on the MB slopes in higher altitudes. They can be interpreted as lower-lying moraines, but this requires another pronounced ice-sheet oscillation after its final retreat, which was not documented in Patagonian Ice Sheet chronostratigraphy. Thus, we interpret them as Toreva blocks. Documentation and granulometric analysis of natural outcrops in rock avalanche bodies show that typical features, i.e. blocky, jigsaw and fragmented facies are present throughout the depth along whole travel distances of rock avalanches. Fragmented facies with jigsaw-fractured blocks and preserved original lithology sequence are most frequent. Sedimentary facies are very similar in all of the studied rock avalanches, which collapsed from bedrock MB slopes, regardless of their age or size.

How to cite: Kapustová, V., Pánek, T., Břežný, M., Schönfeldt, E., Winocur, D., and Smedley, R.: Chronology and sedimentary characteristics of rock avalanches from Meseta Belgrano to Lago Pueyrredón Valley, Patagonia, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8920, https://doi.org/10.5194/egusphere-egu22-8920, 2022.

The grain size of sediment delivered to a river by hillslope processes is crucial for fluvial erosion, sediment transport and associated geomorphic changes. Grain size distribution (GSD) is increasingly recognized an important factor for the impact of landslides on sediment pulses and long-term erosion rates. Therefore a better understanding of grain size control on landslide generated sediment transport and dynamics is crucial and imperative for post-seismic fluvial process and landscape evolution. In this study, we modelled the recovery of the Hongxi river catchment affected by landslides triggered from the Wenchuan Earthquake under different GSD scenarios. Using the CAESAR-Lisflood (CL) model we simulated three different GSD scenarios (Original, Coarser, Finer) by altering original sediment GSD data set observed from a post-earthquake basin. In particular we analysed the fate of landslide-generated sediment using a new sediment tracing function embedded in CAESAR-Lisflood. This enabled us to evaluate the role of landslide GSD variation on the spatial-temporal heterogeneity of sediment transport and landform changes. Our results show that the GSD variations of landslide material exerts an evident impact on both sediment yield and spatial distribution of sediment transport with Finer scenarios showing an overall higher sediment yield. The content of fine sediment display a predominant control when the daily sediment yield is less than 5*10 m³ at the basin outlet. The impact of GSD on sediment transport process varies from landslide to landslide based on their characteristics. These findings highlight the importance of grain size distribution of landslide material and thus shed some light to determine the complete role of landslides on basin sediment dynamics.

How to cite: Xie, J. and Coulthard, T.: How landslide debris grainsize controls sediment transport and dynamics, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6550, https://doi.org/10.5194/egusphere-egu22-6550, 2022.

Inland waters play a vital role in the global carbon cycling. Mountainous rivers act as active pipelines for the transportation of sediments and elements from the mountains through the plains to be ultimately processed and buried along the coasts. During this transit, various in situ biogeochemical processes govern the alterations of the suspended and dissolved matter (and associated organic and inorganic components) and in the process exchange major GHGs (CH₄, CO₂ and N₂O) with the atmosphere. Due to changing climate and the associated shifts in the flow regime of the world rivers, it is essential to revisit the mechanisms by which carbon is being transported along the river continuum and further constrain the effects of regional climate and lithology on the rates of transport and processing. The rivers originating from the Tibetan plateau and the Himalayan region play a dominant role in continental weathering, and represent some of the highest rates among the large river systems across the globe.

            In the present study, an attempt has been made to estimate the concentrations and fluxes of dissolved inorganic carbon (DIC) in the Jhelum River (a tributary of the Indus River) along with its major tributaries (Sindh, Liddar, Vishav, and Rambiara) situated in the Kashmir valley of the western Himalaya. The Jhelum River drains a distinct terrain of recent alluvium to a thick loess deposit, which is assumed to have a significant contribution to the inorganic carbon loading into the river. Furthermore, the flow velocity of the river and turbidity varies along its continuum resulting in a strong coupling of respiration and primary production. We used the miller-tans plots (a graphical mixing model) to identify the sources of inorganic carbon in different reaches along the continuum. Preliminary results from ~ 50 sites and three major seasons in the valley indicate DIC source with isotopically enriched signature (d¹³C_DIC ~ – 2.1 to –3.7 ‰) in the Sind and Lidder catchments whereas a depleted source in the mainstem of the river (d¹³C_DIC ~ –7.1 ‰).

How to cite: Sarkar, S., Shah, R. A., and Kumar, S.: Sources and transformation of dissolved inorganic carbon in a Himalayan river system, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12674, https://doi.org/10.5194/egusphere-egu22-12674, 2022.

Denudation, including both chemical and mechanical processes, is controlled by a range of environmental drivers and is in most environments and landscapes worldwide significantly affected by anthropogenic activities. In the boreal mountain environment of central Norway the regulated lake Selbusjøen, situated at ca. 160 m a.s.l. with an area of 58 km² and connecting the upstream main mountain river Nea and the downstream main river Nidelva, forms a significant sink for sediments being transferred from its drainage basin area of in total 2876 km².  The significant sediment trapping efficiency of lake Selbusjøen is causing a sediment deficit and locally increased fluvial erosion and down-cutting in the downstream river Nidelva which drains into the Trondheim fjord.

This ongoing GFL research on contemporary denudation rates in undisturbed and anthropogenically modified surface areas of the boreal mountain basin of lake Selbusjøen builds on year-round process geomorphological field work including high-resolution monitoring of runoff, solute and sediment fluxes in selected catchments or drainage areas draining into Selbusjøen. The selected catchment or drainage area systems are characterized by high shares of surface areas with a nearly closed and continuous vegetation cover mostly composed of boreal forests and bogs, and represent a range of different catchment sizes, catchment morphometries, orientations/aspects, and sediment sources and sediment availabilities. Different types and intensities of direct anthropogenic impacts like, e.g., agriculture, forestry, and modifications of natural stream channels (e.g., dams, steps, bank protection) and channel discharge for water power purposes are found in the different selected catchments.

Runoff is occurring year-round and the natural runoff regime is clearly nival. Most fluvial transport is occurring during peak-runoff events generated by snowmelt, rainfall events or combinations of snowmelt and rainfall.  Altogether, chemical denudation is moderate but dominates clearly over mechanical fluvial denudation. While chemical denudation is not significantly affected by anthropogenic impacts, mechanical fluvial denudation shows significantly higher rates in surface areas that are modified by anthropogenic activities like agriculture and forestry. At the same time, anthropogenic stream channel and channel discharge modifications are leading to reduced fluvial bedload transport rates into lake Selbusjøen.

Ongoing and accelerated climate change with the related changes of the current wind, temperature and precipitation regimes are expected to increase fluvial denudation and sediment transport rates into lake Selbusjøen, particularly in surface areas that have been modified by anthropogenic activities.

How to cite: Beylich, A. A. and Laute, K.: Contemporary denudation rates in undisturbed and anthropogenically modified surface areas of the boreal mountain basin of a regulated lake system in central Norway, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1766, https://doi.org/10.5194/egusphere-egu22-1766, 2022.

In mountain regions, landslides are enhancing the short- to long-term slope denudation and sediment delivery, conditioning the general landscape evolution; meanwhile, their regional typological patterns should be properly incorporated into single- to multi-hazard evaluations for a proper mitigation of consequences and risk management strategies development.  The Carpathians are an elongate and twisted young mountainous chain of Europe, which is continuing the Alpine orogenetic system towards the internal, Central and Eastern parts of the continent, covering parts of Austria, Czech Republic, Slovakia, Poland, Ukraine, Romania and Serbia. Their heterogeneous morphological and litho-structural forming conditions, the regional climatic traits and the extremely complex and complicated political and socio-economical development stages resulted in a landslide-prone environment, as outlined through numerous scientific works. Nevertheless, there is little synthesis information which can allow a clear evaluation of the entire mountain chain, highlighting the importance of such a study in the present-day context of climate variability and change analysis. As part of the broad landslide typological spectrum, the deep-seated landslides are important paleo-environmental witnesses which may offer substantial information within the risk management and resilience construction context under the modern challenges of climate change impact evaluation. The complexity (many times site-specific) of deep-seated landslides susceptibility and hazard evaluation is enhanced by the (very) high magnitude of such processes, marking with a substantial share the evolution of the coupled slope and channel morphodynamic systems, an interface usually prone to the development of human activities, thus driving the fundamental understanding of their morphogenesis towards highly applied exposure analysis, vulnerability evaluations and risk mitigation concerns. In order to obtain a full extent evaluation of the implication of deep-seated landslides in hazard assessment, a consistent literature review was performed. Several key-issues in understanding the complexity of hazard evaluation, from inventory to susceptibility and frequency/magnitude or triggering thresholds and their return periods were studied: predisposition traits (structure, lithology, terrain/elevation models), preparing conditions (neotectonics, seismicity, human influence, climate variability), triggering factors (precipitation and climate change, earthquakes, anthropic activities), landslide inventories (graphic representations and spatio-temporal coverage), susceptibility modelling (in terms of methods, purpose, units, validation methods, existence of sensitivity analysis), triggering thresholds (scale, typologically-adapted or not, theoretical/validated, recurrences, EWS or  forecast systems) and hazard evaluation (scale, typologically-adapted or not, theoretical/validated, expressed in terms of  susceptibility, relative hazard or hazard). The purpose of this paper is to harmonize for the first time at the entire mountain chain’s continental scale the information concerning the role of deep-seated landslides inside the complex hazard assessment framework. A special attention is directed towards climate variability/change related implications, since the Carpathians, through their more internal, continental position, are representing a key environment for the assessment of continental climate change adaptation strategies.

How to cite: Vasile, M., Sîrbu, F., Popescu, R., Micu, D., and Micu, M.: Review on deep-seated landslides in the Carpathians under climate variability/change and their implication in hazard assessment, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-348, https://doi.org/10.5194/egusphere-egu22-348, 2022.

Extreme precipitation and resulting extraordinary discharge on July 15^th 2021 caused serious flooding and erosion in the northern foreland of the Eifel Mountains, western Germany. We provide two examples of strong backward erosion and sedimentation events from two open cast mining areas in North Rhine-Westphalia (NRW). The first one from the catchment of the Inde River close to Lamersdorf and the lignite open cast mining Inden; the second one from the catchment area of the Erft River near the village of Blessem and the local gravel mining. On-site fieldwork was supported by surveys of unoccupied aerial systems (UAS). Subsequent structure-from-motion (SfM) analyses were compared with the 1 m digital elevation model of the state NRW to estimate size and volume of the erosion and to provide the basis for a geomorphological mapping approach.

At the Inde River between 1998 and 2005 a new river course was created due to the eastward extension of the lignite mining Inden. The 4 km long course of the Inde River was abandoned and today the river relocation, “new Inde River”, passes the mining area in a ~12 km long river bend to the west. At the junction of the new and old river course a flood protection dam was constructed to avoid the flooding of the lignite mining. After heavy rainfall on July 15^th bankfull discharge of the Inde River resulted in a spill over at the junction and the reoccupation of parts of the old river channel. As the lignite mining is more than 200 m below the surface, rapid erosion of the old channel and fast backward erosion creates a 540 m long gorge which was about 5 m deep. More than 500.000 m³ of material were eroded and subsequently accumulated in the lignite mining area.

At the Erft River flooding of a 60 m deep gravel pit occurred and backward erosion quickly reaches the nearby settlement Blessem resulting in the destruction and damage of several houses. In Blessem, first the settling basin of the gravel pit was flooded on July 15^th 2021, resulting in backward erosion of the flood protection dams and finally in a large canyon. An area of more than 7 ha eroded until a depth of 8 m to max. 14m and more than 530,000 m³ sediment were transported into the nearby gravel pit. The new erosion level of the Erft River was about 3 m below its previous base. The original 60 m deep gravel pit was filled with water and about 30 meters of sediments. The digital elevation model and the aerial images indicate three morphdynamic phases of this flood event, with different direction of backward erosion and sediment transport.

Both areas show semi-circle like structures caused by the backward erosion at the headwalls. Immediately deposited material in the headwalls during the event slowed down the erosion processes. Both examples show the high risk and strong geomorphological processes in flooded open-cast mining areas with large base-level changes on short distances.

How to cite: Lehmkuhl, F., Stauch, G., Schulte, P., Wolf, S., and Brüll, C.: Enormous erosion in mining areas during the 2021 July flood in western Germany: Examples from the Inde and Erft River, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4510, https://doi.org/10.5194/egusphere-egu22-4510, 2022.

 Recultivation is a strategy for restoring near-natural landscape systems in anthropogenically influenced environments. Especially in post-mining landscapes after open pit mining, recultivation gives opportunities and potential for near-natural landscape modeling. In order to evaluate the success of the applied measures, biological monitoring approaches with a focus on biodiversity are often carried out. However, the loss of natural soils, which are the result of long-term formation, is an irreversible damage to the pedosphere. The natural soil functions must be completely re-established and it is difficult to examine its success. In our study we therefore investigated initial soil formation in an morphodynamically active artificial river valley, modeled and constructed with a recultivation substrate called “Forstkies”. The study area is located in the catchment of the Inde River (North Rhine-Westphalia, Western Germany), which is part of the international River Basin District Meuse. Due to the progress of the open pit lignite mining, a 5 km long river course had to be relocated. With the aim of creating a near-natural landscape and an appropriate development corridor for the river, a ~ 12 km long river relocation was designed. The artificial river section "Neue Inde" is still geomorphologically naïve and characterized by temporary, highly energetic morphodynamic processes resulting in strong erosion processes in the river bed and the surrounding area. To characterize the morphodynamics and to detect initial soil formation processes, we analyzed a transect of seven soil profiles. The transect includes floodplains and slope areas further away from the river. Allochthonous flood sediments can be differentiated from the underlying artificial Forstkies sediments by inherited contamination of the heavy metals Pb, Zn and Cu. By means of common soil parameters (grain size, CaCO₃, total organic carbon, pH value and sediment colors) and geochemical weathering indices, first initial post-sedimentary alterations can be detected. The quality of the soils is absolutely appropriate to the state of development. The results obtained can be helpful for the planning of future renaturation in post-mining landscapes.  

How to cite: Schulte, P., Hamacher, H., Lehmkuhl, F., and Esser, V.: Initial soil formation in an artificial river valley - Interplay of anthropogenic landscape shaping and fluvial dynamics, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5075, https://doi.org/10.5194/egusphere-egu22-5075, 2022.

The impact of discrete extreme meteorological events on the long-term evolution of landscapes and sedimentary budget is poorly understood. We need quantitative estimates of the geomorphic change occurring during such events, of the sediment fluxes produced by landslides, flashfloods, and sediment remobilization. The frequency of such events at the geological and historical time scale and how they can be driven by climate change is also a major concern, especially for risk management. ¹⁰Be concentrations measured in river sediments produced during extreme events may provide a powerful tool to quantitatively study the geomorphic impact of the event.

On October 2-3 2020, the Var catchment in the French Alps was struck by an extreme rainfall episode connected to the "Alex" storm (> 500 mm / 24h). This event resulted in flash floods in the Vésubie and Var valleys, mobilizing large volume of sediments and resulting in a 10 km long sedimentary plume at the Var outlet in the Mediterranean Sea. Fortunately, the Var catchment had been extensively studied before this event: ¹⁰Be had been measured in sediments to derive sub-catchment denudation rates and interannual variability of the ¹⁰Be signal (Mariotti et al., 2019). Moreover, paleo denudation rates over the last 75 ka for the whole catchment had also been measured using two sediments cores drilled in the Mediterranean Sea (Mariotti et al., 2021), providing a high-resolution record of past sedimentary dynamics. This extreme rainfall event of October 2020 and our previous ¹⁰Be dataset offer the unique opportunity to assess the sensibility of a sedimentary system and its capacity to relay extreme events in a source-to-sink system. This is also a great opportunity to characterize the ¹⁰Be geochemical signature of such events. This step is important to interpret paleo-¹⁰Be signals in sedimentary archives, with the aim to better assess the frequency of extreme events at the geological time scale.

In order to characterize the response of the Var system to the Alex event, we compare ¹⁰Be concentrations in samples taken in 2016, 2017 and 2018 with ¹⁰Be concentrations in samples taken at the same locations after the 2020 storm at +7 days, +21 days, +4 months and +7 months. We use also use samples taken within each sub-catchments to constrain the evolution of the ¹⁰Be signal over time. This dataset permits to define the background of the ¹⁰Be concentrations and compare these concentrations to the ones measured after the storm. The ¹⁰Be concentrations measured at the outlet of the Var catchment at +7 days and +21 days are similar to those measured before the storm. However, the sample taken +4 months later shows a 20% decrease in ¹⁰Be concentration from pre-storm values. The Vésubie sub-basin is the only one to exhibit a ¹⁰Be decrease at +21 days. Hence, the delayed depletion observed at the outlet probably reflects the transfer of a ¹⁰Be-depleted sediment-wave from the Vésubie valley, where most of the landslides and terraces reworking happened during the storm.

How to cite: Mariotti, A., Blard, P.-H., Charreau, J., Petit, C., and Aster, T.: Impact of an extreme storm on the 10Be signal in a mountainous catchment, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5240, https://doi.org/10.5194/egusphere-egu22-5240, 2022.

Landslides are very efficient in shaping mountain landscapes, modifying the drainage pattern of the valleys, forcing people to adapt, react or counter them. In particular, valleys in the southern side of the Alps are narrow, with very steep slopes, and often have been inhabited since prehistoric times.

The Tovel Valley is located in the Adamello Brenta Nature Park in the northern Brenta Dolomites, near a lake (Tovel lake) that is famous for its, at times, red colour. This valley can be found in the central-eastern Southern Alps, along the western margin of the Adriatic indenter. Here, tectonic forces started to act in the Late Cretaceous, during the initial phases of the Alpine orogenic history, and are still active today. Moreover, the Trentino Region is one of the most seismically active sectors of Northern Italy, with significant historical and instrumental earthquakes typically clustered in very good agreement with tectonic structures. N-S oriented vertical strike-slip faults determined the shape of the Tovel Valley, favouring the occurrence of prominent source detachment scarps on the eastern valley side. The Tovel lake, whose origin is still debated if due to glacial processes or landslide events, records a sudden rise in its level, testified by the drowning of a submerged forest dated by dendrochronology at 1597 AD. This event is interpreted as due to a minor rockfall, which blocked the outflow channel on the north-eastern lakeside. This event had direct consequences on people living in the area, that were forced to find timber elsewhere, but also older, and larger, rock avalanches likely affected people living in the valley.

Whilst Tovel lake has been studied for a long time, the blocky deposits of the Tovel Valley gathered much less attention. By means of field mapping, remote sensing and cosmogenic ³⁶Cl exposure dating, we reconstruct the age and the evolution of the blocky deposits that occupy large areas of the valley bottom, with implications directly connected to the formation and evolution of the Tovel lake. Landslide deposits cover an area of ~5 km² and are composed of seven bodies distributed at different elevations, ranging from ~1900 to ~900 m a.s.l. Their total volume is estimated at 200–280 Mm³ of debris made of Dolomia Principale and Calcare di Zu Formations. Detachment areas are mainly located along the eastern valley side, with six out of seven events that can be classified as rock avalanches.

How to cite: Rossato, S., Martin, S., Ivy-Ochs, S., Viganò, A., Campedel, P., and Rigo, M.: Landslides in the Tovel Valley: shaping the landscape and ruling the people, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4280, https://doi.org/10.5194/egusphere-egu22-4280, 2022.

River Ganges, being one of the largest trans-boundary river, flows along the northern part of the Indian subcontinent contributes sediment to, one of the largest alluvial basin in the world, the Indo-Gangetic basin. The basin is composed of sediments sourced from the Himalayas and also from peninsular India. This river has experienced rapid and multiple migrations through its geological history and varied fluvial geomorphic processes, tectonic controls and complex climatic interplay have led to the deposition of different lithofacies within this Central Ganges basin (CGB). A provenance study has been started in the CGB in order to understand its geological evolution and reconstruct the regional paleo-environment through subsurface lithostratigraphy. Initial X-ray diffraction data of borehole sediments in CGB shows dominant presence of quartz, feldspar, mica and heavy minerals in varying proportions at different depths. Substantial amounts of kaolinite, smectite, illite and montmorilonite are found in descending proportions within the upper clay layers, where abundance of kaolinite is significantly higher over the other minerals. The upper layers till ~30m comprises of clay having particle size of 2.42μm- 3.12μm, below which are mostly silt and sand layers ranging from 16.4 μm -1.63mm, with fine intercalations of gravel and clay layers in-between.The upper layers are dominated by muscovite indicating a Himalayan origin of the sediments, which shows a sharp decline in abundance below 100 m bgl. Moreover, presence of only zircon as heavy mineral is noted within 100m bgl. In contrast, beyond 100m bgl, the sediments are represented by very low mica content, abundance of pyroxene, and heavy minerals like zircon, rutile, illmanite, and sphene possibly signifying contribution from cratonic areas. Significant quantities of recrystallized and highly altered quartz-feldspathic mass showing clear evidence of strain, are also observed. The disposition of sediments from multiple provenances confirms significant contribution of sediment load from southern tributaries of the Ganges river system which eventually diminishes with time due to temporal and spatial migration of the river.

How to cite: Bose, O., Mukherjee, A., Sengupta, P., Shaw, A., Das, P., Layek, M. K., and Smith, M.: Understanding sedimentary provenance and sub-surface lithostratigraphy of Central Gangetic Basin, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1991, https://doi.org/10.5194/egusphere-egu22-1991, 2022.

In mountain drainage basins, constraining source-to-sink sediment fluxes over decadal time scales is critical for evaluating hillslope and fluvial response to ongoing climate change and holds practical implications for sediment management. To this end, we combine geomorphic change detection (GCD) (Wheaton et al., 2010) and sediment provenance analysis in the reservoirs of Gioveretto (1850 m a.s.l.), Vernago (1665 m a.s.l.) and San Valentino (1499 m a.s.l.), western South Tyrol, Italy. The reservoirs are located in the Austroalpine domain and the main outcropping lithologies consist of metamorphic rocks (e.g., metapelites and gneisses).

Through GCD analysis conducted on recently acquired lake-bottom DTMs (i.e., SfM-UAV and multibeam surveys) and pre-dam (i.e., contour-based) counterparts, we have mapped the spatial distribution of erosion and deposition, and have assessed the relevant sediment yields over the last six decades. The three systems, which drain areas of 69 km² (Vernago), 77 km² (Gioveretto) and 163 km² (San Valentino), exhibit varying degree of glacier extent, and have experienced a different history of lake-bottom anthropogenic disturbance. Preliminary, conservative GCD results constrain net aggradation volumes that correspond to sediment yields of 35*10³ m³/yr at Gioveretto (1954-2019), and 68*10³ m³/yr at San Valentino (1959-2020). In this context, the much lower figure of 6.5*10³ m³/yr (1962-2021) at Vernago refers to a small portion (20%) of the lake bottom, which was spared from sediment removal during maintenance work occurred in 2001-2002.

To quantify the contribution of each tributary stream to the sediment yield in each reservoir, quantitative provenance analysis was carried out on 18 sand/silt samples collected from fluvial bars of major tributaries and on the 3 reservoirs. The similarity between petrographic composition of river sediments supplied by different combinations of diverse end-member sources (e.g., parent lithologies) and the observed detrital mode of the sediments in the reservoirs was quantified using a statistical distance. Next, the relative contribution to the total sediment load from each of these tributaries was calculated by forward mixing modelling (Garzanti et al., 2012). Sediments in the study streams are dominated by quartz, feldspars, and metamorphic lithic grains. Heavy minerals include hornblende, garnet, and epidote. Results of the provenance analysis indicate that in Lakes San Valentino, Gioveretto and Vernago, the dominant contributions derive respectively from Rio Carlino (Mt. Palla Bianca – Weißkugel; 3738 m a.s.l.), Rio Plima (Mt. Cevedale – Zufallspitze; 3769 m a.s.l) and Tisentalbach (Mt. Similaun 3607 m a.s.l). This contribution is part of the SedInOut project (2019-2022), funded through the V-A Italia-Österreich Interreg Programme (European Regional Development Fund). Modern bathymetric data, processed by Cartorender Srl, are kindly made available by Alperia Srl.

References

Garzanti E., Resentini A., Vezzoli G., Andò S., Malusà M., and Padoan M. 2012. Forward compositional modelling of Alpine orogenic sediments. Sedimentary Geology, 280, 149-164.

Wheaton J.M., Brasington J., Darby S.E., Sear D.A. 2010. Accounting for uncertainty in DEMs from repeat topographic surveys: improved sediment budgets. Earth Surface Processes and Landforms, 35, 136-156.

How to cite: Brardinoni, F., Llena, M., Mair, V., and Vezzoli, G.: Decadal sedimentary yield and provenance in the Gioveretto, San Valentino and Vernago reservoirs, western South Tyrol, Italy, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6098, https://doi.org/10.5194/egusphere-egu22-6098, 2022.

Tailings are a by-product of the processing of minerals at mine sites and are usually fine grained, contain water and processing chemical residues and are usually very erodible. Tailings are commonly stored in ‘tailings dams’ and these dams are a feature of many mine sites. These dams are in a geomorphic disequilibrium and have similar risk to that of water storage dams with geotechnical, seismic, hydrological (rainfall) and erosional induced failure concerns. These dams also pose a risk of release of polluted water and the accompanying chemicals and fines.  At the majority of mine sites tailings dams will be permanent geomorphological features which do not geomorphologically integrate with the surrounding landscape. A dam has a design life and it has been suggested that closure designs be considered for a 1000 year design life with other sites considered for 10 000 year scenarios. New methods are therefore needed for assessing long-term behaviour of anthropogenic structures such as tailings dams. Computer based Landscape Evolution Models (LEMs) are a new tool to assess tailings dam design.  These models provide information on type of erosion and erosion location as well as erosion rates. Models such as CAESAR-Lisflood can also provide information on water quality and stream sediment loads and models the transport of all size fractions. The model can therefore provide guidance on long-term behaviour, which allow designs to be tested and improved accordingly. The work uses CAESAR-Lisflood to examines a series of hypothetical tailings dams subject to a range of different possible rainfall scenarios. The findings demonstrate that without maintenance the dam wall will be breached at a time exceeding the dam life design for average conditions but may breach within decades for an extreme (yet possible) event. For both cases water quality will be reduced for centuries post breach and may never reach background (pre breach) levels representing a permanent change in water quality. The modelling here provides a method for the assessment of not just tailings dams but other anthropogenic structures and their geomorphological behaviour. The work here also raises questions about landscape stewardship for such altered systems.

How to cite: Hancock, G. and Coulthard, T.: Anthroprogenic landscapes: assessing the geomorphological stability of tailings dams using a Landscape Evolution Model, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6548, https://doi.org/10.5194/egusphere-egu22-6548, 2022.

Many rivers in Chilean Patagonia are difficult to access, experience high flow variability and frequent sudden floods, which make traditional grain size distribution sampling and analysis extremely challenging. There are several diverse methods and software that attempt to determine grain size using analysis of photographs. Manual methods, although of high precision, are extremely labour and time intensive as they process particle by particle by hand. On the other hand, automated methods although fast, still produce low precision in particle identification and size determination, This motivated us on developing a field and desktop method that is fast, precise and requires light equipment. It includes good natural light management with a light and inexpensive kit, considering a good representative selection of the study site. Preliminary to the automated method, the photographic sample is calibrated regarding tones, colours and brightness, with the aim of generating high contrast between clasts and therefore an easier recognition by the software ImageJ. We tested the method with 50 photographs analysed with manual and other (semi)automated methods, characterizing the surface depoosits of río Simpson between the towns of El Blanco and Coyhaique, in Chilean Patagonia. We identified and mapped sediment patches using an UAV. Results show that our method has a lower error and processing time. Ongoing challenges include the underestimation in size and number of some clasts, and overestimation of sand, with respect to the manual method, but it still outperforms other (semi)automatic methods.

How to cite: Jullian, A., Fortini, F., Quezada, P., Dussaillant, A., Gonzales, C., and Chavez, P.: A new photo-sieving approach: quick and effective semi-automated method for gran size counting for gravel beds, and application to a Chilean Patagonia river, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10893, https://doi.org/10.5194/egusphere-egu22-10893, 2022.

Rivers transport large amounts of fine mineral and organic matter in suspension from their sources to the ocean. Suspended solids, which also bind contaminants and nutrients, therefore, affect river morphodynamics, water quality and ecosystem functioning. A detailed understanding of suspended solid dynamics is urgently needed to improve suspended sediment monitoring and management around the world.

Sediment rating curves (SSC=aQ^b) describe the relation between suspended solid concentrations (SSC) and river discharge (Q) and are frequently used to study suspended sediment dynamics at specific location in a river. In this formula, a and b are regression coefficients that depend on river basin characteristics. The a-parameter is an indicator of the erosion severity and the b-parameter reflects the erosion reactivity with respect to changing discharge. To date, a few studies have compared the rating parameters (a and b) to catchment characteristics, however, these studies only focused on specific regions on earth. A global study is required to better understand suspended sediment dynamics along a wide range of catchments characteristics.

In this study, we compiled available SSC and Q data from 176 rivers that are located in various regions around the world. The majority of the SSC and Q data have been collected from the GEMStat and the Global Runoff Data Centre (GRCD) databases, but we also included data from the USGS and SO-HYBAM datasets. The compiled dataset ranges from small basins (~50 km²) to large basins (~190,000 km²), with medium-sized river basins (~1000-10,000 km²) being most dominant. Furthermore, the dataset contains basins that are located in various climate regions, ranging from semi-arid to humid climate, and includes both upland and lowland rivers. We only included river monitoring stations with >50 overlapping SSC and Q data points (i.e., SSC and Q data measured on the same day). We parameterized the rating curve between the SSC and Q data and compared the a- and b-parameters to topographic, lithologic, climatic and land cover-related catchment characteristics using simple and multiple linear regressions.

The first results reveal that the b-exponent and, thus, the suspended solids variability, shows a fairly good relationship with catchment steepness and basin size. The data suggests that climatic and land use parameters play an insignificant role, however, when combining all parameters in a multiple linear model, climate seems to have a secondary effect on top of topographic parameters. The erosion severity (a-parameter) is most strongly controlled by climatic and land cover parameters. The results of this study can be used to infer for suspended sediment dynamics in ungauged catchments, which is relevant for implementing sediment monitoring and management in these regions on earth.

How to cite: van Dongen, R., Hoffmann, T., and Dietrich, S.: Global variations in SSC-Q relationships and the controlling catchment characteristics, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11706, https://doi.org/10.5194/egusphere-egu22-11706, 2022.

Suspended sediment transport is a vital process in healthy river systems as it provides a source of nutrients in the soils of riverbanks and floodplains that eventually forms the principal building material of downstream river deltas. Deltas require sufficient sediment supply from the upstream river basin to sustain area and elevation on the long-term. Recent decades, the delivery of suspended sediment to many deltas in the world has decreased, which, together with sediment extraction through dredging, resulted in negative sediment budgets of these deltas. To design strategies to attenuate or reverse the decreased sediment delivery, a quantitative understanding of the sources, fluxes, and budget of suspended sediment in river basins is essesntial.

The aim of this study is to quantify the contribution of different tributaries to the suspended sediment budget in the Rhine river basin between 1995 and 2015. For this, we used fortnightly to monthly measurements of suspended sediment concentrations and daily discharge measurements at 34 stations along the main branch of the Rhine river and its four major tributaries Aare, Neckar, Main, Mosel. Annual suspended sediment loads were estimated by means of the sediment rating curve method, which allowed establishing the annual sediment budgets for 28 river sections.

For the first time we were able to show the relative contribution of different tributaries to the overall decreasing suspended sediment load of the upper Rhine river (between 1995 and 2015). A decline of 70% percent in suspended sediment at Lobith between 1950 and 2016 and an observed consistent decline further upstream suggests an overall decline of sediment delivered to the lower lying delta. The causes must be sought in basin wide changes such as land-use, land management, hydrology, or climate. This is a trend that is observed in many river basins in recent decades.

How to cite: Edler, T., Van der Perk, M., and Middelkoop, H.: Trends in suspended sediment fluxes and sediment budgets across the river Rhine basin (1990-present), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12005, https://doi.org/10.5194/egusphere-egu22-12005, 2022.

Among the greatest stressors on global riverine sediment transport are the 48,000+ existing large dams and the ~3,700 dams that are planned or under construction. They directly obstruct sediment flowing to the ocean, alter downstream flow regimes, modify sediment carrying capacities, trigger hazardous bank erosion and riverbed incision, and influence river water quality. Understanding the role of dams in sediment retention is crucial for quantifying the anthropogenic influences on global fluvial systems. Representation of sediment trapping by dams is currently a major source of bias in continental- and global-scale hydro-geomorphic modeling frameworks. This study focuses on developing a new reservoir trapping efficiency (Te) parameter to account for the impacts of sediment trapping behind dams in hydrological modeling efforts. This will be done by harnessing a novel remote sensing data product, developed using Machine Learning within Google Earth Engine (GEE) to generate high-resolution and spatially continuous maps of sediment concentration across the CONUS. Sediment trapping is calculated for 400+ dams across the CONUS using pre-reservoir and post-dam sediment fluxes, and various explanatory variables including attributes of dams, topography, land use and land cover characteristics, soil parameters, and fluvial properties, are evaluated to estimate their contribution for predicting sediment trapping. This study provides a robust framework for isolating and quantifying the influence of anthropogenic factors on fluvial fluxes by informing more realistic trapping of sediment at dam locations.

How to cite: Moragoda, N., Cohen, S., and Gardner, J.: Development of a New Reservoir Trapping Efficiency Parameter for Large Scale Sediment Modeling using Remote Sensing of Fluvial Sediment, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10636, https://doi.org/10.5194/egusphere-egu22-10636, 2022.

As part of a large research project reconstructing fault slip rates, palaeoseismiology and landscape evolution in New Zealand, we have developed a range of new chronological tools with applications to sediment. These closely related methods are based on Infra-Red Stimulated Luminescence (IRSL) signals of alkali feldspar, and allow us to determine aspects of transport and burial at the scale of individual grains over time periods ranging from 1 to 300,000 years. In particular, we have introduced and tested a method referred to as 3ET-IRSL (Three Elevated Temperature IRSL), and we are also applying a MET-IRSL (Multiple Elevated Temperature IRSL) approach comprising measurement sequences that include five IRSL measurements at different temperatures. These techniques can be used in different ways to filter complex single grain IRSL apparent age distributions that arise from processes including short duration reworking associated with incomplete trapped charge removal during transport. These methods were primarily designed to improve chronological control for sediment dating in contexts where conventional approaches encounter significant challenges owing to the geomorphic setting including high volume, rapid deposition. However, these approaches can provide significant insight into the dynamics of sediment transport routes and rates at the individual grain scale. We will demonstrate the performance of these methods at key test sites, and assess the implications of our findings in New Zealand (NZ), coupling observations of relict fluvial terrace formation with landscape response to the Mw 7.8 Kaikoura earthquake of 2016. At one of our NZ sites, fluvial system response to this event is the opposite of that expected from the literature in terms of sediment deposition and erosion; the degree to which this represents a transient response is assessed. We highlight the amazing potential of these new tools for improving our understanding of source-to-sink sediment transport dynamics.

How to cite: Rhodes, E., Ivester, A., Dolan, J., Gauriau, J., Van Dissen, R., and Little, T.: New luminescence chronological tools for dating and tracing sediment movement, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12285, https://doi.org/10.5194/egusphere-egu22-12285, 2022.