Sand transport and its deposition in deep marine basins is controlled by diverse climatic, tectonic, physiographic and oceanographic processes. Disentangling the impact of each of these drivers on the sedimentary record is a fundamental challenge in the study of source to sink systems. In this study, we investigate seismic and boreholes data using statistical and spectral analysis approaches to identify the factors controlling sand deposition in the deep Levant Basin (Eastern Mediterranean) during the Pliocene-Quaternary (PQ). We interpret the sand content in boreholes from Gamma Ray (GR) logs and identify two major trends in sand/shale ratio. On a million-year scale, we demonstrate that since the Early Pliocene (5.3 Ma) sand content gradually increased until it formed a ~100 m thick widespread sand sheet at the top of the section. On a shorter time-scale, we identify oscillations in sand content depicting statistically significant power of periodic components at the 350-450, 90-150, and 10s ka bands. The long-term increase in sand content reaching the deep Levant Basin is interpreted as a result of the Nile Delta propagation, which had continuously shortened the distance between the Nile delta edge that became the source of sand, and the deep Levant Basin. The superimposed short-term oscillations are interpreted as Milinković cycles that produced hydrologic oscillations of water and sediment discharge into the Eastern Mediterranean Sea by the Nile River. This demonstrates the hydroclimatic control on sand deposition in the deep Levant Basin. Our observations are consistent with the development of a submarine channel system along with the accretion of the Nile delta, which may have served as a pathway for sand delivery via high energy turbidite currents that reached the Levant Basin.    

How to cite: Sirota, I., Ben Dor, Y., and Gvirtzman, Z.: Short-term climatic oscillations versus long-term delta propagation: what controls sand transport into the deep Levant Basin since the Pliocene? , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1886, https://doi.org/10.5194/egusphere-egu24-1886, 2024.

Since the early 2000s, the development of the Source-to-Sink (S2S) approach improved the understanding of variations in the sedimentary signal and its controlling factors within coupled catchment-sedimentary system. However, S2S study remains difficult, as the data and time scales of the distinct compartments of the system may be incompatible, poorly resolved or even lacking. The combined quantification of sediment budget in both the catchment’ and sedimentary basin’s parts of the system is a way to address this problematic.

The aim of this study is (i) to jointly measure erosion and sediment deposition across an entire S2S system, and subsequently (ii) discuss the influencing factors and the mode of signal propagation. The study focuses on the system of Sithas (Corinth rift, Greece), where numerous geomorphologic markers (e.g., marine terraces) provide constrains to quantify eroded volumes, and a large offshore dataset is available to establish well-constrained sedimentary budget.

To achieve this, we updated an age model for the last 800 ka. We then restored the volumes of sediment eroded in the catchment and quantified the volumes of sediment deposited offshore to estimate fluxes of sediments from the source and the sink during the last 800 ka Quaternary climatic cycles. We also compared these results with a multi-regression empirical model estimating suspended sediment loads (BQART).

Erosion (source) and sediment (sink) fluxes have shown a gradual increase since 800 ka: from 3km³/Ma for the source and from 1. to 75. km³/Ma in the deep-sea fan (sink). This overall increasing trend is superimposed by cyclic variations, in both erosion and deposition signals. Significant increases in fluxes are observed over periods of around 12 ka every 120 ka (at circa 10, 120, 230 and 340 ka), which are followed by a progressive decrease. They coincide respectively with high sea levels according to the global eustatic curve (odd Marine Isotopic Stages). Surprisingly, the peaks of fluxes in deposition (sink) are preserved prior to the peaks of fluxes in erosion (source) with a time lag of around 30 ka. The comparison with BQART fluxes also shows the significant influence of the catchment size and the climatic factors such as temperature and precipitations in modulating the signal propagation.

These observations suggest that even for small, coupled catchment-deep sea fan system, the signal propagation is not straightforward, and thus deserves much more attention in future works.

How to cite: Deiss, N., Rohais, S., and Regard, V.: Source-to-Sink signal propagation in a coupled catchment-deep-sea fan system: the Sithas example from the Corinth Rift (Pleistocene, Greece), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5232, https://doi.org/10.5194/egusphere-egu24-5232, 2024.

Sediment connectivity is an important property of geomorphic systems reflecting the potential to route material through themselves and hence modulating the propagation of geomorphic changes. While the relevance of the concept is clear, connectivity cannot be measured directly and the discussion on the best methods to quantify connectivity is still ongoing. Probably the most frequently used approach is based on the index of connectivity (IC) as it was developed by Borselli et al. (2008) and later adapted by Cavalli et al. (2013) for alpine catchments. This index aims at quantifying the structural connectivity that is governed by the spatial configuration and properties of system components. Nevertheless, the predictive capabilities of this index for functional connectivity, i.e. the actual transfer of sediment between the system components, have not been conclusively validated with field data. Most importantly, previous studies have, to our knowledge, not taken into account the spatial variability of the hydrometeorological forcing that leads to different functional connectivity in locations with similar structural connectivity.
In this study, we use a unique dataset to test the predictive capability of the IC for hillslope-channel coupling of debris flows in the Horlachtal, Austria (described by Rom et al., 2023). The dataset consists of aerial imagery and two airborne LiDAR digital elevation models from which n=156 debris flows were mapped and quantified that were triggered by intense rainstorms on July 20th and 23rd, 2022. For this event, adjusted radar data (INCA data from the Austrian meteorological survey, ZAMG, and measurements from weather stations within the study area) give a high-resolution account of the spatial distribution of rainfall intensities and sums. Using these data, each debris flow was characterised with respect to (i) the meteorological forcing that affected its contributing area, (ii) morphometric properties of the latter, (iii) its sediment volume, and (iv) its runout length indicating functional connectivity, i.e. the degree of coupling to the main channel. Then we assessed the influence of structural connectivity (indicated by the IC) and hydrometeorological forcing on the observed functional connectivity. To our knowledge, this is the first study investigating the predictive capacity of the IC taking into account the spatial variability of the forcing. Among others, our results show that the IC is significantly higher for those debris flows that reached the main channel, compared to those that did not.

How to cite: Himmelstoss, T., Rom, J., Kara, D.-E., Betz, S., Altmann, M., Haas, F., Becht, M., and Heckmann, T.: Testing the predictive capability of the Index of Connectivity (IC) on a 2022 debris-flow event considering the spatial variability of the forcing, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7410, https://doi.org/10.5194/egusphere-egu24-7410, 2024.

River discharge patterns are sensitive to changing precipitation as a result of evolving climates. In stratigraphy, the intermittency factor (I_f) of ancient rivers can help illuminate landscape dynamics in the past. The I_f is recorded in the geologic archive as the ratio of average transport rates (from long-term records of water or sediment flux) versus instantaneous maximum transport capacities if they were to be sustained over the same period, and applying intermittency calculations to stratigraphy can reveal how rivers and landscapes recorded and responded to external tectono-climatic forcings. Here we explore the Lower Eocene Castissent Formation of the Southern Pyrenees, Spain, a strongly progradational fluvio-deltaic succession deposited during the Early Eocene Climatic Optimum (EECO), an intense warm period analogous to potential future climate scenarios. We first reconstruct the depositional volumes of the Castissent Formation in the Tremp-Graus Basin and its equivalent marine successions in the Ainsa and Jaca Basins. We then compare these to estimates of instantaneous water and sediment fluxes using field-based quantitative palaeohydrology approaches.  From these reconstructions, we derive fluvial intermittency factors which we compare to river data for a range of climate conditions. Further, we present detailed reconstructions of morphodynamics in these lower Eocene rivers during the EECO. These results add to growing understanding of intermittency in the geologic past, and reveal the sensitivity of rivers and landscapes to climate forcing in a warm world analogue.  

How to cite: McLeod, J., Whittaker, A., Bell, R., Hampson, G., Fuller-Field, O., Prieur, M., and Valero, L.: Palaeohydrology and Fluvial Intermittency in the Eocene Hothouse: Castissent Formation, Southern Pyrenees, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7862, https://doi.org/10.5194/egusphere-egu24-7862, 2024.

The Kalahari Basin in southern Africa, shaped by subsidence and epeirogeny, features the Okavango Rift Zone (ORZ) as a significant structural element characterized by diffused extensional deformation forming a prominent depocenter. This study elucidates the Pleistocene landscape evolution of the ORZ by examining the chronology of sediment formation and filling this incipient rift and its surroundings.

Modeling cosmogenic nuclide concentrations in surficial aeolian sand from distinct structural blocks around the ORZ provides insights into sand’s residence time on the surface. Sand formation occurred from ~2.2 to 1.1 Ma, coinciding with regional tectonic events. Notably, provenance analyses of sand within ORZ's lowermost block where large alluvial fans are found indicate different source rocks and depositional environments than those of the more elevated aeolian sand. This suggests that the major phase of rift subsidence and the following incision of alluvial systems into the rift occurred after aeolian dune formation. Luminescence dating reveals that deposition in alluvial fan settings in the incised landscape began not later than ~250 ka, and that a lacustrine environment existed since at least ~140 ka.

The established chronological framework constrains the geomorphological effects of the different tectono-climatic forces that shaped this nascent rifting area. It highlights two pronounced stages of landscape development, with the most recent major deformation event in the evolving rift probably occurring during the middle Pleistocene transition (1.2-0.75 Ma). This event is reflected as a striking change in the depositional environments due to the configurational changes accompanying rift progression.

How to cite: Vainer, S., Schmidt, C., Garzanti, E., Ben Dor, Y., Pastore, G., Mokatse, T., Prud'homme, C., Léanni, L., King, G., and Verrecchia, E.: Sedimentary systems archive the chronology of landscape evolution in the developing Okavango Rift Zone in southern Africa , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8037, https://doi.org/10.5194/egusphere-egu24-8037, 2024.

Despite the fact that large dams exert a significant environmental impact on the rivers they impound, a renewed 21^st century interest in these hydraulic structures exists, mainly driven by the premise to make the agricultural and energy sectors climate-resilient. This study focuses on the often underexposed large dams in Africa and entails an examination of their spatial distribution and characteristics, and downstream impacts. To this end, we have created a comprehensive spatial database of 1047 large dams, which can be considered the most complete database for Africa. Together, these dams impound 949 km³ of water for irrigation (50% of dams), urban and industrial water supply (31% of dams), hydropower generation (16% of dams, with a total installed capacity of 43,567 MW) and other purposes (< 3% of dams). The findings of our systematic literature review of the hydrological and geomorphological impact of these large dams reveal a consistent augmentation in low flows, a pronounced reduction in high flows, and often, a decrease in average river flows. Furthermore, sediment trapping efficiencies within the range of 60% to 99% are documented. Although these trends exhibit broad consistency across the continent, the associated geomorphological changes frequently exhibit localized variations. Common alterations encompass riverbed incision and a narrowing of the active riverbed. Coastal erosion and the permanent opening or closing of estuaries are also recurrently observed. Additionally, a spectrum of ecological impacts is identified, ranging from thermal and hypoxia pollution to shifts in riparian woody vegetation distribution, often favouring non-native species. Although there is no one-size-fits-all solution to address these environmental externalities, our study highlights the importance of environmental impact assessments, monitoring of dam-induced impacts and environmental justice. Furthermore, the study offers insights into potential forthcoming challenges in the context of a changing climate  (32% and 44% of the dams respectively expect significant precipitation increases and decreases by 2050) and ever-high sediment yields (at 73% of the dam locations, sediment yields above 10 Mg km^-2 yr^-1 occur). These challenges necessitate adaptive dam operation strategies and transboundary management, and additional efforts to deal with reservoir sedimentation.

How to cite: Frankl, A. and Annys, S.: A systematic review of the hydrological and geomorphological impact of large dams in Africa, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9145, https://doi.org/10.5194/egusphere-egu24-9145, 2024.

Depending on their geometry, in-stream large wood (LW) pieces can significantly influence the morphology and hydraulic properties, the water and sediment connectivity of river channels as well as the riverine biodiversity. Such depositions often form hydraulic resistance, change the flow velocity and reduce the transport capacity. This, in turn, might affect the water and sediment connectivity of a channel, resulting in increased sediment deposition. Furthermore, LW can form new morphological structures, such as riffles or pools or alter already existing ones, for example river banks. The deposition of LW in streams is also associated with positive effects on biodiversity, as changes in the channel and flow patterns can significantly improve the heterogeneity of habitats.
In Europe, a lack of studies related to in-stream wood and its effects on channel morphology and sediment connectivity exists, as most research on this topic has been conducted in North America. In addition, the predominantly applied methodology is very time-consuming and complex, as the influence of LW is mostly based on the determination of drag force. The aim of this study is therefore, to apply a simple method to investigate the influence of LW on water and sediment connectivity in small streams in the Vienna Woods (Austria). Furthermore, geomorphological mapping is used to asses the effects of LW on channel morphology.
The study has been conducted in four mid-mountain streams of the Vienna Woods, located in the vicinity of the city of Vienna (Austria). LW deposits and potential sediment sources are mapped, classified and counted according to predefined criteria. Sediment deposits are measured and visible morphological changes, both associated with LW, are documented. The collected data is then used to (1) create a map, indicating LW accumulations in the research area; (2) determine the amount of retained material; and (3) apply the recently introduced indices ID_LW (LW disconnectivity index) and RP_LW (LW sediment retention potential index) (Pöppl et al., 2024) to gain an overview over the disconnectivity and sediment retention potential the LW deposits exhibit.
First results of this study will be presented at the EGU General Assembly 2024.

Reference: Pöppl, R.E., Perez, J., Fergg, H., Morche, D. (2024) Introducing indices to assess the effects of in-stream large wood on water and sediment connectivity in small streams. Geomorphology 444, 108936

How to cite: Diem, S., Chmela, S., and Pöppl, R.: Assessing the influence of large wood on sediment connectivity and river morphology in small streams in the Vienna Woods (Austria), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10473, https://doi.org/10.5194/egusphere-egu24-10473, 2024.

At the foot of a mountain range, rivers sometimes cut several hundred meters into alluvial fans. This incision reflects a transition from aggradation to erosion, possibly as a result from a major change in external conditions. The incision of rivers into alluvial fans has often been interpreted as the result of a deficit in sediment supply during the transition from glacial to interglacial periods, associated with an increase in water discharge. However, such incision is not observed along all mountain fronts, nor at the mouth of all the catchment areas along a same mountain range. The conditions that lead to incision of alluvial fan are still poorly  quantified.

We tackle this question by means of a laboratory-scale device in which a 40x60cm block is uplifted at a constant rate under artificial precipitation, forming a mountainous landscape. Additionally, the products of its erosion are deposited on a plateau surrounding the block, forming alluvial fans and a piedmont. We carried out 8 experiments (700 to 900 min-long) in which the rate of precipitation was either constant or alternated between periods of low precipitation P1 and high precipitation P2, of variable duration from 10 to 40 minutes. The topography of experiments was monitored over time by using a high-resolution laser sheet. Sediment and water fluxes Qs and Qw at catchments’ outlet were computed over time from topographic and rainfall data.

We observe a variability in the relationships between Qs and Qw between catchments, due to some spatial heterogeneities in precipitation rate and migration of ridgelines. Qs and Qw vary in phase with precipitation cycles, but with different amplitudes between catchments. When the system reaches a state of dynamic equilibrium, the piedmont is a bypass for the sediments. Its average slope is inversely proportional to the average rainfall rate.

Only 8 deep incision events occurred at the outlet of certain catchments in the piedmont in all our experiments. We show that these incisions only occur for a certain slope threshold during dynamic equilibrium, and for a certain percentage decrease in sediment concentration d(Qs/Qw). These incisions never occurred in the two constant precipitation experiments and only initiated during P2 precipitation periods.

On the basis of the slope of the alluvial fans S at dynamic equilibrium, we calibrated a sediment transport law for the piedmont in the form of an excess shear stress power law. Using this law, we used a Monte Carlo approach to simulate many pairs (S , d(Qs/Qw)), for which we calculated the ratio between sediment transport capacity and flux, and the Froude number. We show that the incisions occurring in our experiments correspond to a transition towards an excess of transport capacity, for Froude numbers approaching 1. It has recently been shown that a river bed becomes unstable for such values, driving incision and knickpoints. Our experiments and theoretical analysis are consistent with this interpretation, which explains why incision occurs rarely in our experiments. These results offer new perspectives for quantitatively interpreting the incisions observed in nature in terms of paleo-fluxes Qs and Qw.

How to cite: Zavala, V., Bonnet, S., and Carretier, S.: Alluvial fan river incision during climatic change: new clue from an experimental erosion device, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3050, https://doi.org/10.5194/egusphere-egu24-3050, 2024.

 In the semiarid climate of Central Asia the rivers and their associated floodplain ecosystems have a high relevance as regional hotspots of biodiversity and for the provision of ecosystem services. One of these rivers is the Naryn River in Kyrgyzstan which is part of the headwaters of the Aral Sea basin. Upstream of the Toktogul Reservoir, which is the first barrier in the river course, the Naryn is still in a nearly natural state over a length of 600 km. The valuable floodplain habitats directly depend on the natural dynamics of this river. In particular rejuvenation and thus community structure of floodplain forests depends on the interaction of flow regime and hydromorphology controlled by longitudinal and lateral connectivity of water and sediment. Despite the ecological relevance, riparian ecosystems along the Naryn have not been investigated yet in detail. Especially the relative importance of the ecological and physical processes as well as anthropogenic effects on floodplain forest succession trajectories are not yet understood. This is a crucial issue for biodiversity conservation and environmental management as ongoing plans for additional dam construction are likely to heavily modify hydrologic and sediment connectivity. This is likely to have significant downstream impacts such as channel incision caused by sediment deficit or modification of the hydrological regime. The modifications therefore impact the current natural riparian ecosystem structure and functioning. In this study, we contribute to fill this knowledge gap and develop a conceptual succession model for this semiarid floodplain forest explaining the recent shape and distribution of habitat patterns. For this purpose, we use detailed ecological information derived from field data collected on 44 plots in the floodplain forest of the central Naryn basin together with river corridor scale remote sensing analysis using Sentinel-2 for detailed habitat derivation. These assessments are complemented by Landsat time series analysis with the LandTrendr segmentation algorithm to gain insights on large-scale spatio-temporal dynamics of vegetation and hydromorphology. Based on the results, we were able to determine the relevance of local morphology for longitudinal habitat patterns and to quantify the relationship between lateral connectivity and floodplain forest community structure at the scale of an entire river corridor. The conceptual model derived from the results explains the complex longitudinal and lateral pattern as well as the succession trajectories of floodplain forest communities along the Naryn River. It helps to better understand the natural processes and potential effects of anthropogenic activities to support forest and biodiversity conservation. In addition, it provides a basis for further research in other semiarid floodplain ecosystems.

How to cite: Lauermann, M., Betz, F., and Heckmann, T.: Channel-floodplain connectivity drives vegetation dynamics in semiarid floodplains: a remote sensing analysis of the Naryn river corridor in Kyrgyzstan, Central Asia, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12086, https://doi.org/10.5194/egusphere-egu24-12086, 2024.

The climate-tectonic-sea level relationship in an active mountain belt, like the Himalayas and its foreland, can be better understood by delving into the sedimentary stratigraphy of the alluvial tracts developed in the foreland basins. Alluvial fans, in particular, operate as a natural depository of sediments that can be utilized to assess the role of geological processes working between the source and sink. The physiography of these fans, including channel patterns, aggradation, and incision, is influenced by tectonics, sea level variations, and local factors like precipitation and slope, impacting the availability of eroded materials. This study based on geomorphic mapping, detailed sedimentological analysis, lithofacies analysis, and geochemical (Sr-Nd analysis) provenance characterization, as well as optically stimulated luminescence (OSL) ages of a relict alluvial fan, provides a dated sedimentation framework for the western Assam lowland areas. The fan surface lies ~40 m above mean sea level, is incised, and forms a regional valley terrace T₁ composed of meandering channel deposits. Modern braided rivers flow on the T₀ surface. The findings suggest that the alluvial fan is composed of three distinct lithofacies associations and aggraded during 27 to 3 ka. The bottom-most cross-bedded gravelly-sandy facies (Phase-1) indicate progradation of the fan during LGM, owing to the increased gradient of the Himalaya-bound rivers. Sheet flood deposits (Phase-2) in the middle facies formed during the Late Pleistocene-early Holocene with rising sea levels and increased precipitation. In the Mid-Late Holocene, the uppermost facies (Phase-3) deposited as rivers, responding to elevated sea levels, lost their gradient, leading to inland sedimentation within muddy meandering channels. Modern-day Gravel Sand transition zone lies much upstream of the transverse rivers in comparison to the gravel sand transition zone of the paleofan. This indicates that alluvial fan was prograding in response of increased gradient of the transverse Himalayan Rivers due to lowered sea level during LGM.  Our analysis found that falling sea level during the late Holocene was associated with greater precipitation and allowed the river to incise, to form gullies over the fan surface and form the valley terrace T₁. The gravel units found in borehole stratigraphy of Upper Bengal Delta (located ~100 m below msl) relate to progradation of alluvial fans in response to lowered sea-level rather than an extreme flood events in axial channel of Brahmaputra as envisaged in earlier study. The provenance fingerprinting using Sr-Nd isotopic composition suggest that the deposits of phase-1 and phase-2 were equally sourced from the Higher and lesser Himalaya while the phase-3 deposit along with the sediments of the meander scroll deposit mimicked the composition of the modern-day bed-load which are dominated by Higher Himalayan sediments. 

How to cite: Panda, S., Srivastava, P., Kumar, A., and Pulpadan, Y. A.: Sea Level-Influenced Sedimentation in the Lower Brahmaputra Foreland Basin: Unraveling Dynamics and Provenance, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12148, https://doi.org/10.5194/egusphere-egu24-12148, 2024.

Tropical Africa is globally one of the most sensitive regions for soil erosion and is characterised by an important yield gap. Rapid population growth is expected to triple food demands in Sub-Saharan Africa by 2050. These rising food demands need to be met by cropland that is highly prone to soil erosion. In particular, the White Nile-Congo ridge region between the DR Congo and Uganda is a hotspot for issues relating to food security linked to massive soil degradation due to steep terrain, highly erosive rainfall and low soil cover conditions. Despite its importance, most soil erosion studies in the region are based on plot or large-scale modelling studies. Both approaches lack information on inter-field connectivity processes, which are especially important in smallholder farming structures where the average field size is 0.1 ha. To address this, a UAV-based monitoring campaign was carried out over different cropland sites (two in the DR Congo and two in Uganda) at high spatial and temporal resolution. The campaign covered more than 500 individual fields which were monitored twice per month (for two years) using UAV-based aerial photography to get insights into event-based rill erosion processes and the role of landscape connectivity. The aerial photography data was classified according to its field condition: (i) vegetation covered, (ii) bare soil without signs of rill erosion, (iii) field with rill erosion. The results highlight the relevance of land cover patchiness due to smallholder farming structures on inter-field connectivity with rill erosion often discontinuing downslope across field boundaries. Therefore, rill development is highly localised and affects individual fields. We further conclude that rill erosion in the White Nile-Congo ridge region is not an episodic process but takes place regularly during the rainy season as a result of high frequency erosive rainfall (on average 20 erosive rainfall events per rainy season) falling on bare soil in fields that are left fallow for individual cultivation periods. Soil erosion dynamics in the study area are complex and controlled by processes that are challenging to be represented in large scale predictions on soil degradation.

How to cite: Wilken, F., Fiener, P., Batista, P., Cooper, M., Haist, J., Muhindo, D., van Oost, K., Rueegg, M., and Doetterl, S.: Rill erosion and its structural inter-field connectivity in the White Nile-Congo ridge region – two years of high frequency UAV monitoring, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14462, https://doi.org/10.5194/egusphere-egu24-14462, 2024.

Climate variations and escalating anthropogenic pressures stand out as two major factors driving the heightened occurrence and severity of highly destructive events. The increase in the intensity of rainfall phenomena leads to an imbalance in river systems, which are progressively prone to a rise in flood events, consequently elevating the likelihood of inundation, especially in small mountain catchments  characterised generally by high levels of (geological and hydrological) heterogeneity. This is the case in the Marche Region (central Italy), where in the last few years, high precipitation amounts were recorded in a very short time, leading to critical situations in the involved river basins. The most damaging occurred in September 2022 with flood events in the Candigliano, Cesano, Misa, and Sentino basins. The most significant damage due to sediment transport occurred in the municipality of Cantiano due to the flooding of the Burano River, the Candigliano River’s main tributary. Extraordinary rainfall was recorded close to the anticline of Mount Catria; the amount was about 30% of the annual precipitation, approximately 419 mm of rain. This event resulted in about 13 fatalities, 50 injuries and critical damages to infrastructure. A large amount of even coarse sediments with calcareous compositions have been mobilized causing the occlusion of the minor channels that have caused the leakage of water and accumulation in depression areas. Hence, the importance of studying these systems through a more detailed geomorphological approach trying to understand the evolutionary processes of the landscape. The proposed methodology consists of assessing the connection of sediments fusing the Connectivity Index (IC) toolbox defined by Cavalli et al. (2013) and its interpretation in light of the existing morphological context. The connection index represents the probability that particles near the river will end up there. By characterizing IC, it is possible to estimate the input of material into the riverbed, define the source areas of material, and study the transfer paths. In the mountain systems, the morphology is complex and constantly evolving; the spatial connectivity of the sediment is translated through the transfer of material on the slopes, in the valleys, and along the network of channels (e.g., catchment outlet, main channel network, a given cross-section along the channel). Using the toolbox, the geomorphological indices called weighted factors, i.e., rasters that are based on surface characteristics influencing the processes of runoff and inflow of sediment within a basin or on a slope (e.g., roughness, slope, lithology, curvature, land use, Italian Landslide Inventory (IFFI), etc.) were analysed. An integrated approach allowed to evaluate the connectivity of the sediments and to highlight the source areas, which is extremely useful for defining the general availability of sediments, the potential for achievement, and management priorities in ordinary conditions and emergency situations.

How to cite: Guidi, E., Teloni, S., Pappafico, G., and Morelli, S.: GIS-Based analysis of sediment connectivity in small mountain catchments of Metauro River (northern Apennines, Italy), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20022, https://doi.org/10.5194/egusphere-egu24-20022, 2024.

Tectonic, climatic, and anthropogenic forcing generate sediment flux signals that propagate across the Earth’s surface. Some of these signals get stored in strata but autogenic processes in operation at the Earth's surface can shred (i.e. degrade) and obscure many signals of environmental change prior to stratigraphic storage. Here we advance on earlier seminal work and use a physical rice pile to identify critical autogenic timescales and establish autogenic thresholds that can be used to understand of how a signal of a given period or magnitude is manifested in an efflux time series and whether or not a signal is shredded or obscured by autogenic noise. Time-permitting there will be a more general discussion on how this applies to landscapes and strata.

How to cite: Duller, R., Griffin, C., and Straub, K.: A Framework for Signal Shredding and Signal Detection Using a Physical Avalanching Rice Pile, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20212, https://doi.org/10.5194/egusphere-egu24-20212, 2024.

Since the 1970s, the Mississippi Alluvial Plain (MAP - a US EPA Level III Ecoregion) has experienced significant agricultural intensification via irrigation practices. The MAP overlies the Mississippi River Valley Alluvial Aquifer, presently the second most withdrawn aquifer in the USA (~46 million m³ per day). The increased irrigation demand has supported a ~7x increase in irrigated production; whereby, about 70% of all MAP cropland is now irrigated. The irrigation intensification has resulted in similar increases in crop yield. These MAP patterns are exemplified within northwestern portions of the US state of Mississippi, a region referred to as the Mississippi Delta. Within the Mississippi Delta (~18,000 km²), the predominant irrigation application is furrow irrigation, which has been facilitated by precision land leveling. As such, berms are typically placed around the lower elevations of the leveled field to detain runoff. Runoff is then slowly released through one (or more) outlets into a ditch or other drainage system. Consequently, the current topography and hydrography of the Mississippi Delta is vastly different  from historical records and remains dynamic. The alterations in surface hydrology and hydrologic connectivity will also influence how sediments, nutrients, and other agrochemicals are processed ecologically. The size of the Mississippi Delta limits comprehensive monitoring of runoff, transport, and transformation processes across the entire landscape. Therefore, scientists at the U.S. Department of Agriculture, Agricultural Research Service, National Sedimentation Laboratory are developing computer models and supporting databases to evaluate those controlling processes at the basin scale. Current US national databases of surface hydrography in the Mississippi Delta (e.g., the National Hydrography Dataset Plus High Resolution; NHDPlus HR) are based on elevation data (10 m resolution digital elevation model) collected before land leveling. Hence, the NHDPlus HR drainage model is too coarse, and significantly differs from reality. Using machine learning (ML) technology we have characterized the drainage network from high-resolution lidar data (avg. point density > 2 points/m²) collected during the period 2018-2020. The ML-derived drainage model includes ditches (as narrow as 3 m) and identifies field outlets. To assess how surface hydrology and connectivity have changed, and possible implications on water quantity and quality, we are building two HEC-RAS models using the pre-1970 hydrography and the 2018-2020 hydrography. Our test case features the 12-digit hydrologic unit code (HUC) subwatershed: Roundaway Bayou-Quiver River (HUC # 080302070805; surface area is ~162 square kilometers), which occupies central portions of the Mississippi Delta. Because HEC-RAS accounts for the effects of subgrid-scale topography on surface runoff, we can accurately describe the 2018-2020 high-resolution (1 m horizontal) topography and hydrography at larger spatial resolution; in our simulations we therefore used a grid with cells of 10 m horizontal resolution. We will present results on the changes in surface runoff (magnitude, direction, retention, and connectivity) and implications for water quantity and quality in the Mississippi Delta region.

How to cite: Langendoen, E., Heintzman, L., Witthaus, L., Moore, M., Greenwood, K., Li, D., and Fang, N.: The impact of agricultural intensification on hydrologic disconnectivity in the Mississippi Delta region of the Mississippi Alluvial Plain, USA, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20677, https://doi.org/10.5194/egusphere-egu24-20677, 2024.

River captures reroute river networks and generate transient pulses of erosion. Their frequency, size, and spatial distribution are also important drivers of freshwater biodiversity. How tectonic, climatic, or autogenic processes influence the frequency-magnitude and spatial distribution of river capture events are unexplored gaps in landscape evolution research with cross-disciplinary implications. Using numerical modeling of landscape evolution in Landlab, I apply the simplest form of the stream power equation to explore the sensitivity of river captures to the exhumation of rocks with higher resistance to erosion (i.e. a lower erodibility parameter – K). The exhumation of heterogenous rock types in a slowly eroding landscape allows for a positive feedback loop to evolve until some drainage basins completely shrink while others expand. In these conditions, the exhumation of a resistant rock intersects river systems with differing incision capacities, thus creating differential relief across drainage divides and initiating divide migration. The continuous drainage area loss enhances drainage divide migration and increases the probability of river captures. For the same background erosion rate, doubling the areal extent of the exhumed resistant rock nearly triples the probability of large river captures and quadruples the size of the largest river capture of the model run. Lastly, the mode of drainage area exchange (i.e. divide migration or river capture) is itself sensitive to the degree of base-level perturbation caused by the exhumation of a resistant rock. In tectonically inactive settings with low erosion rates, the complex spatial distribution of rocks can thus create spatially variable frequency-magnitude distributions of river captures. These preliminary findings reveal an exciting avenue for exploring the origins and sensitivity of river captures to autogenic controls and its consequences for sedimentary fluxes and biogeography.

How to cite: Val, P.: River capture frequency and magnitudes are regulated by rock erodibility, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21535, https://doi.org/10.5194/egusphere-egu24-21535, 2024.

Fluvial fans, as opposed to alluvial fans, have only been recognised over the past two decades as important end members in the classification of alluvial-fluvial landforms. There is still a lack of knowledge regarding the factors driving their formation, their geomorphology, stratigraphic build-up and significance as quantitative recorders of terrestrial (sub)orbital climate change. Here, we present a stratigraphical and grain-size analysis of ~5,000 gravel clasts of the Lima fluvial fan in Peru. An age-depth, and derived sedimentation rate, model was constructed by means of Monte Carlo Markov Chain iterations of thirteen, new luminescence ages of the fluvial fan. Our data showed near-continuous sedimentation from 121.7 ± 4 ka at the base of the exposed stratigraphic section at 10 m above sea level (asl) until 6.3 ± 1.6 ka at the top (62.5 m asl). Stratigraphical unconformities, both erosional and non-erosional, systematically coincided with the initiation of coarsening upward sequences as shown by increases in the D₅₀ grain size. The unconformities and coarsening-upward sequences, in turn, coincided with both orbital and suborbital pluvial periods, as known from Peruvian lake and speleothem records. The precession cycle was the primary driver for increased precipitation, runoff and modelled sedimentation rates during the lower half of the last glacial period, coinciding with the Ouki and Salinas pluvial periods. Imprinted on the precession cycle, one-to-five-ka long suborbital pluvial periods constituted a secondary driver, coinciding with the stratigraphical unconformities and increases in D₅₀ grain size. Throughout the Salinas wet phase, the amplitude of the precession cycle diminished and, at the end of it, the precession cycle ceased altogether to be a driver for fluvial sedimentation. From 50 ka onwards, stratigraphical unconformities, coarsening upward cycles and an increase in sedimentation rate systematically coincided with the onset of the Atlantic Heinrich events, which have been recognised as three-to-five-ka long pluvial events in the aforementioned lake and speleothem records. Most fluvial sedimentation events have been recognised in fragmentary records of other fluvial systems in Peru, but the Lima fan constitutes the most complete fluvial record to date. As such, the Lima stratigraphical record shows the value of fluvial fans as quantitative recorders of fluvial landscape change due to last glacial climate cyclicity.              

How to cite: Viveen, W., Sanjurjo-Sanchez, J., Bravo-Lembcke, G., and Uribe-Ventura, R.: Fluvial fans as stratigraphic recorders of suborbital climate cyclicity: an example from the Lima fluvial fan in Peru, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4449, https://doi.org/10.5194/egusphere-egu24-4449, 2024.