Coastal and inland surface water resources are affected by complex and overlapping processes such as climate change, droughts, flooding, river damming, coastal expansion, dredging, river meander migration, and so on. The use of satellite-acquired imagery, combined with recent advances in cloud computing, is enabling the monitoring on a global scale of areas where water limits have advanced or receded (Donchyts et al., 2016; Donchyts et al., 2022; Pekel et al., 2016). However, previous studies have not estimated an important aspect: the precise timing at which changes in water extents happened. Here we present preliminary results of an analysis using 38 years of Landsat time series and the cloud platform Google Earth Engine (GEE) in which we  monitor areas where water has advanced and receded and the year that this change happened. The developed algorithm detects only permanent changes in water features and thus avoids seasonal or higher-frequency fluctuations caused by short-lived events. The method employs a two-step algorithm. The first step detects areas of permanent change using the Modified Normalized Different Water Index (mNDWI), which effectively detects water and non-water features. In the areas of detected permanent change, the second step uses a Green-Red Normalized Different Water Index (GR_NDWI), which has a smoother value transition from water to land, to identify the year that the change happened. The thresholds of mNDWI and GR_NDWI used to determine if a pixel is water or not were estimated using the Otsu method. Furthermore, an additional novel algorithm was developed to fill in cloud holes in the time series, allowing the monitoring of cloudy regions, such as the Amazon Basin. The final product will be a World Map of the year that the water advanced or receded. A preliminary result for the American continent (excluding Canada)  can be visualized in this app: https://gustavoonagel.users.earthengine.app/view/americawaterdetection . The product will be available in a public GEE dataset, for open access use by researchers, governments, and private companies working on oceans, rivers and water lakes, helping to improve water management on a global scale.

Donchyts, G., Baart, F., Winsemius, H., Gorelick, N., Kwadijk, J., & van de Giesen, N. (2016). Earth's surface water change over the past 30 years. Nature Climate Change, 6(9), 810-813. https://doi.org/10.1038/nclimate3111

Donchyts, G., Winsemius, H., Baart, F., Dahm, R., Schellekens, J., Gorelick, N., Iceland, C., & Schmeier, S. (2022). High-resolution surface water dynamics in Earth’s small and medium-sized reservoirs. Scientific Reports, 12(1), 13776. https://doi.org/10.1038/s41598-022-17074-6

Pekel, J.-F., Cottam, A., Gorelick, N., & Belward, A. S. (2016). High-resolution mapping of global surface water and its long-term changes. Nature, 540(7633), 418-422. https://doi.org/10.1038/nature20584

How to cite: Nagel, G., Darby, S., and Leyland, J.: A global analysis of the timing of changes in water extents using Google Earth Engine and Landsat Time Series., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4438, https://doi.org/10.5194/egusphere-egu23-4438, 2023.

Geomorphologists have long debated the relative importance of disturbance magnitude, duration and frequency in shaping landscapes; for channel change during single floods, it is thought that flood duration, rather than magnitude, matters most. However, studies of flood-induced channel change have often drawn upon small datasets. By using satellite data to track channel adjustment during floods, we can now query these classic hypotheses with large datasets, and we do so here by combining 7 years of Sentinel-2 images with daily flow data from laterally active rivers. Using Earth Engine, we apply automated algorithms to map river planforms and detect their lateral shifting, and we generate a large dataset to quantify channel change during ~1000 flood events in gauged rivers across New Zealand and the Americas. We draw upon this dataset to evaluate how characteristics of the flood hydrograph (including magnitude, duration, and integrated sediment transport) correlate with the degree of geomorphic change observed. Finally, we examine the potential of predictive models for geomorphic change during floods, and consider the variables that moderate this relation between flood character and geomorphic change.

How to cite: Leenman, A., Slater, L., Dadson, S., and Wortmann, M.: Quantifying 'effective' floods using large-sample geomorphology, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1146, https://doi.org/10.5194/egusphere-egu23-1146, 2023.

Lowland rivers have been extensively affected by anthropic pressures in many regions of the Earth. The aim of this work is to investigate how a sequence of multiple anthropic pressures that took place on a single river sector can generate mutual feedbacks determining unplanned channel configurations. To enlighten this topic, we reconstructed the last century evolutionary trajectory and the historical human impacts that affected a 121 km length sector of the Po River (Northern Italy).

Two main groups of anthropic pressures acted on the study sector. An extensive training scheme was implemented from the 1930s to the 1950s along a multi-thread sector of the Po River to ensure its permanent navigability by bent navigation structures placed within the active channel, which concentrated the water flow during low discharge conditions into a single sinuous channel. Then, other human activities were carried out for exploiting sediment (in-channel mining) and water (dams’ construction) resources, inducing a dramatic reduction of sediment availability and fluxes along the river. Such activities had a peak of intensity from the 1960s to the 1970s.

Our results show an evolution from predominantly anabranching or wandering patterns in the 1950s to a single-thread configuration at the beginning of the 21th century, accompanied by remarkable narrowing (about -50%) of the active channel. This evolution has been interpreted as follow:  Riverbed lowering occurred exclusively in the main channel in the 1970s and the training works enhanced the disconnection and deactivation of the secondary channels that were located behind and protected by the navigation structures. This localized incision of about -4 m of the active channel was determined by the profound sediment starvation caused by in-channel mining and dams’ construction. In the absence of the navigation structures, it is likely that the channel adjustments would have been less profound, with more homogeneous and less intense riverbed incision along the entire active channel, partial maintenance of activity in the secondary channels and, therefore, potential preservation of the multi-tread patterns characterizing the river sector in the first half of the 20th century.

The current single thread sinuous pattern of the study sector is then the result of these two specific anthropic pressures that acted –and interacted– during the 20th century in this portion of the river. The morphological modifications that led to this result can then be defined as unplanned, that is, not designed but fortuitously caused by multiple diachronous impacts acting on the same river sector for different human purposes. The lesson learned from the Po River suggests that anthropogenic-unplanned channel configurations can represent a common type of riverscape in densely inhabited areas significantly affecting recovery potential and future geomorphological trajectories. A comprehensive understanding of riverine sedimentary, hydraulic and geomorphological processes represents a crucial aspect for properly managing lowland fluvial systems in the Anthropocene, also with a view to restoration strategies on highly impacted riverscapes.

How to cite: Brenna, A., Bizzi, S., and Surian, N.: How multiple anthropic pressures may produce unplanned channel patterns: A case study from a lowland sector of the Po River (Italy), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9915, https://doi.org/10.5194/egusphere-egu23-9915, 2023.

Lowland rivers regularly flood and create complex inundation patterns where energy and matter are exchanged between landscape patches over a dynamic network of surface‐water connections. Scale‐freeness of networks for phenomena in many disciplines have been studied with mixed results. Here we present the first documented example of a (roughly) scale‐free network of surface‐water connections within a river‐floodplain landscape. We accomplish this by simulating inundation maps across the historical range of flows for the Mission River in Texas. We then analyze the topology of the surface‐water connections between the river and soil and vegetation habitat patch types. Results show that surface‐water connectivity is scale‐free for ≥64% of simulated flows (≥70% for flows with floodplain inundation). Moreover, the dynamic surface‐water connections meet five of the six conceptual criteria of scale‐free networks. Our findings indicate that river‐floodplain landscapes are self‐organizing toward scale‐free surface‐water connections among patches that optimizes energy and matter exchange.

How to cite: Güneralp, I., Castillo, C. R., and Hales, B.: Roughly scale-free network of surface-water connections within a lowland river landscape, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17415, https://doi.org/10.5194/egusphere-egu23-17415, 2023.

While river channel change is a natural process for an alluvial river, increasing human activities such as sediment mining, construction of reservoirs and land use alterations can accelerate this process. Growing urbanization and socio-economic development in South-Eastern Europe over the last 30 years has shown a major impact on the river channel adjustments. New urbanization in Albania has rapidly developed after the collapse of dictatorial regime in 1990, with most rural population moving to the big cites, mostly the nearby capital Tirana and Durres. As consequence a boom in construction industry has occurred in this part of Albania, including new buildings and infrastructures. Rivers have been the primary source of building material. Here we analyse the channel adjustments that occurred on the Erzen River that passes nearby the two major urban centers of Tirana and Durres. The Erzen River has its origin at the Gropa mountain at 1200m asl, its length is 109 km, and it flows approximately westwards towards its mouth in the Adriatic Sea near the Lalzi Bay. The catchment area is 760 km² and the mean annual flow is 18.1 m³/s. We analyse the incision and channel narrowing at lower part of the river by using remote sensing, historical image analyses, DEM and survey in the field. Major hydromorphological pressures potentially affecting the flow and sediment supply regime have been also analysed. Specifically, sediment mining has been reconstructed by identifying the mining sites in contact with the active river corridor between 1990-2015 along 30 km river length from aerial rivers, and from technical reports providing estimation of sand and gravel removed from the river.

Our findings indicate rapid changes of channel morphology, with 20% up to 75% channel narrowing affecting the transitional and meandering reaches between 1968-2015 and high riverbed incision at the reach scale up to 5-6 m, which is also revealed by visual signs like increasing bed rock and bridge foundations exposure. Two cut-offs have been created at the meandering part of the river. Most of the main bridges in Albanian rivers have shown exposed foundation with 3-4 m on the last 15-20 years, where some of them are replaced by other bridges due to unstable structure condition. Compared with previous studies, narrowing and incision rates are among the highest observed in Europe after the 1950s. While on the upstream segment of the river two dams have been built, sediment mining appears as the main driving factors of the observed channel narrowing and incision. Twenty-two mining sites have been detected between 1995 - 2015 and 457,380 m³/year of sediments have been reported as withdrawn from the riverbed. The rapid channel incision has contributed to the increasing salty water intrusion and subsequent freshwater shortage in lowland part of the river. The observed narrowing and incision have likely played a key role also in the reduction of river sediment supply to the sea, which probably explains most of the very rapid coastal erosion that has been observed in the same period in the Lalzi Bay.

How to cite: Cekrezi, B., Zolezzi, G., and Lata, L.: Quantifying recent channel Incision in lowland Erzen River, Albania, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12648, https://doi.org/10.5194/egusphere-egu23-12648, 2023.

The interplay of the hydrology of a great river and tectonics in floodplain setting is always a challenging research topic. The evolution of the river course, development of islands, oxbow lakes, changing channel sinuosity can be evaluated as signals of these two processes. In our study area, we seek to explain the evolutionary history of the Nagy-sziget, Rácalmás, Hungary by using a multidisciplinary approach. We integrate field observations, evaluation of historic maps, and results of our own geophysical measurements in order to reconstruct the environmental history of this island of the river Danube. The investigated island is located south of Budapest, in the southern corner of Csepel Island, where the Soroksári-Danube branch joins the main branch. The area is particularly interesting in geodynamic sense, as the region is crossed by the Mid-Hungarian Mobile Belt at the confluence of the Ráckeve (Soroksári) Danube branch close to the northern part of the island. During the field campaign we observed characteristic micro relief structures in the field that have been integrated with landforms indicated on historical maps. Furthermore, we wanted to know how these topographical patterns continue below the surface, therefore geoelectric measurements were carried out. We conclude that the area of the island started to grow very rapidly after the river regulations. Our geoelectrical tomography and electromagnetic measurements showed that, despite the very low relief, the subsurface geology is reflected in microtopography. Based on these results various scenarios for the formation of the island have been put forward; a final scenario will emerge from our planned measurements. We concluded that the evolution of the Nagy-sziget may have had tectonic, landsliding, sedimentary and flood-related components, which are specific to different regions. With the integrated results of the geoelectric and electromagnetic measurements and the study of historical maps, we managed to reconstruct the growth of the island in unprecedented detail over the past 250 years and we can formulate some implications to a certain extent for periods before written documents.

How to cite: Vitai, Á., Csernyik, L., Visnovitz, F., and Székely, B.: Environmental history and geophysical investigation of the Nagy-sziget, Rácalmás, Hungary, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11927, https://doi.org/10.5194/egusphere-egu23-11927, 2023.

Abandoned river channels on alluvial floodplains represent dynamic systems where sediments, organic matter, and pollutants preferentially accumulate during extreme discharge events. Descriptive models that explain the infilling of these floodplain lakes due to sedimentation processes recognize different stages in their evolution. For example, the threshold for hydrologic connectivity and the transfer of material increases in older lakes as a plug-bar develops. Sedimentary archives collected from floodplain lakes are widely used to reconstruct ecological and hydrologic dynamics in riverine settings, but how floodplain lake evolution influences flow velocities and sedimentation patterns on an event scale remains poorly understood. In this study, we examine a floodplain lake along the Trinity River at Liberty during the extreme flood event associated with the landfall of Hurricane Harvey in August 2017. We combine sediment samples collected in and around a floodplain lake with hydraulic modeling simulations in the HEC-RAS modeling platform from the US Army Corps of Engineers to examine inundation, flow velocity, and sedimentation patterns. Additionally, we develop a series of alternative lake bathymetries to study the influence of floodplain lake evolution on flow velocity patterns during the flood. The hydraulic model reproduces the sediment patterns that we observe around the lake resulting from Hurricane Harvey and matches descriptive models on the behavior of a young floodplain lake. We find that sediments deposited in the lake following the Hurricane Harvey flood become thinner and finer with distance from the lake entrance in accordance with simulated flow velocities that are lower further from the lake entrance. Flow velocity simulations from model runs with alternative plug-bar geometries and lake depths imply that sedimentation patterns will shift as the lake evolves and infills. As the floodplain lake becomes shallower and narrower, flow velocities extend further into the lake resulting in more extensive transport of coarse-grained material into the lake. These simulations are coherent with observed sediment records from lakes in different stages of floodplain lake evolution. The integration of sediment sampling and hydraulic model simulations provides a method to understand the processes that govern sedimentation in floodplain lakes during flood events that will improve interpretations of individual events in sedimentary archives from these contexts.

How to cite: Reinders, J. B., Sullivan, R. M., Winkler, T. S., van Hengstum, P. J., Beighley, R. E., and Munoz, S. E.: A Hydraulic Modelling Approach to Study Flood Sediment Depositions in Floodplain Lakes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8890, https://doi.org/10.5194/egusphere-egu23-8890, 2023.

Streams convey coarse-clastic sediments towards coasts, where interactions with deltaic and coastal processes determine the resultant landscape morphology. Although extracting hydroclimatic signals from landscapes is a desired goal, many studies rely on interpreting paleoclimatic proxies and the link between depositional/geomorphic processes and the hydroclimate remains vague. This is a consequence of the challenge to link processes that often are studied separately, span across large spatial and temporal scales including synoptic-scale hydroclimatic forcing, stream flows, water body hydrodynamics, fluvial and coastal sediment transport, and sedimentation. Here, we explore this chain of connected processes in the unique setting of the Dead Sea basin, where present-day hydroclimatology is tied closely with geomorphic evolution and sediment transport of streams and coasts that rapidly respond to lake-level fall. We use a five-years-long (2018-2022) rich dataset of (i) high-resolution synoptic-scale circulation patterns, (ii) continuous wind-wave and rain-floods records, and (iii) storm-scale fluvial and coastal sediment transport of varied-mass, ‘smart’ and marked boulders. We show that Mediterranean cyclones approaching the eastern Mediterranean are the main circulation pattern that can provide sufficient rainfall and winds that concurrently activate two perpendicular sediment conveyors: fluvial (floods) and coastal (wind-waves). The synoptic-scale westerlies (>10 m s^-1) are orographically funneled inside the Dead Sea rift valley, turning into surface southerlies. They generate 10-30 high-amplitude northward propagating storm waves per winter, with <4 m wave height. Such storms transport cobbles for hundreds of meters alongshore, north of the supplying channel mouths. Towards the decay of the storm wave, the high-altitude synoptic westerlies provide moisture to generate 4-9 flash-floods, delivering unsorted coarse gravels into the basin. These gravels are dispersed alongshore by waves only during subsequent storms. As storm waves dominates and are >five times more frequent than flash-floods, coarse-clastic beach berms and fan-deltas are deposited preferentially north of channel mouths. This depositional architecture, controlled by regional hydroclimate, is identified for both the modern and Late Pleistocene coast and delta environments, implying that the dominance of present-day Mediterranean cyclones has persisted in the region since the Late Pleistocene when Lake Lisan occupied the basin.

How to cite: Eyal, H., Armon, M., Enzel, Y., and G Lensky, N.: Synoptic- to meso-scale circulation connects fluvial and coastal gravel conveyors and directional deposition of coastal landforms in the Dead Sea basin, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13679, https://doi.org/10.5194/egusphere-egu23-13679, 2023.

River bifurcations are ubiquitous features of both gravel-bed and sand-bed fluvial systems, including braided networks, anabranches and deltas. As such, their morphology and development shape fluvial plains and deltas, dictating flood-prone areas as well as land loss and land gain. In this regard, bifurcations worldwide are often found unstable to any perturbation of their current state, leading to highly asymmetric discharge partitions between the branches or ultimately to the complete closure of one of them. However, in tide‐influenced deltas, it has been observed that bifurcations tend to exhibit more stable branches keeping all channels active. Therefore, although the morphodynamic equilibrium of bifurcations is strongly affected by the characteristics of the upstream channel, only lately some effort has been put into studying the action exerted by external forcings in the downstream channels. Ragno et al. (2020), inserting small-amplitude tides in the analytical model of Bolla Pittaluga et al. (2015) of river bifurcations, managed to prove that even small-amplitude tides have a stabilizing effect. In this regard, we aim at extending their analysis to the case of finite amplitude tidal forcing through a series of numerical investigations. Factors such as the length of the downstream channels or different tidal ranges are studied in order to define their influence on the evolution of bifurcations. Results show that present analytical theories are able to reproduce fairly well the increase of stability in small amplitude tidal systems, while they tend to overestimate the stability of bifurcations in higher tidal range ones. Numerical simulations show that, even when a branch gets dry during low tide due to the step formed at the bifurcation node, it might still receive river flow in high tides keeping the typical estuarine environment alive. However, increasing the tidal range to finite amplitudes, estuarine bifurcations are found to be less stable than their pure fluvial counterparts.

How to cite: Durante, L., Bolla Pittaluga, M., and Tambroni, N.: Numerical investigation of tidal forcing on the stability of bifurcations, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7662, https://doi.org/10.5194/egusphere-egu23-7662, 2023.

Around 40% of rivers globally currently have deltas, but the factors that facilitate or prevent delta formation are not well understood. Previous work has suggested that the critical factors governing their formation are (mean annual) fluvial sediment delivery rate, significant wave height, and tidal range (Caldwell et al., 2019). In light of ongoing climate-change driven changes to wave-generating weather, as well as changes to river sediment flux due to land-use change and river management, understanding how variability in these factors affects delta development is critical to developing sound coastal management strategies.

Here a comprehensive set of numerical simulations conducted using Delft3D is presented, with the aim of identifying the limits of the above factors beyond which a delta is prevented from forming. In order to retain a reasonable scope, analysis is restricted to variation of significant wave height and tidal range only, with sediment delivery rate held approximately constant. The resultant depositional landforms are then classified as either deltaic or non-deltaic, based primarily on the ultimate presence or absence of new unsubmerged regions of land. Depositional environments are further classified as river-, wave-, or tide-dominated in order to link delta presence to dominance regime, following the methodology of Nienhuis et al. (2020). Algorithms are also developed to facilitate classification of the resulting depositional features, and metrics are investigated that are time invariant, so as to formalise the process of classification.

Results indicate that increasing significant wave height and tidal range lead to a reduced rate of formation of new unsubmerged land, with higher values preventing the formation of such land altogether. At this point the depositional landform no longer meets the criteria for being defined as a delta.

References
- R. L. Caldwell, D. A. Edmonds, S. Baumgardner, C. Paola, S. Roy, and J. H. Nienhuis. A global
delta dataset and the environmental variables that predict delta formation on marine coastlines.
Earth Surface Dynamics, 7(3):773{787, 2019.
- J. H. Nienhuis, A. D. Ashton, D. A. Edmonds, A. Hoitink, A. J. Kettner, J. C. Rowland, and T. E.
Tornqvist. Global-scale human impact on delta morphology has led to net land area gain. Nature,
577(7791):514-518, 2020.

How to cite: Sloan, E., Dodd, N., and Briganti, R.: Application of numerical modelling to establish the thresholds of delta formation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8360, https://doi.org/10.5194/egusphere-egu23-8360, 2023.

Estuarine dams are dams constructed within the salt or tidal intrusion limits of estuaries for securing freshwater resources or flood control. In this work, we deal with the global distribution of estuarine dams and their sedimentological impact on estuaries. Approximately 10 percent of all estuaries we analyzed (about 2400 estuaries for which river mouth width is greater than 90 m) were affected by estuarine dams and direct human modifications are responsible for more than 1,000 km² of the observed estuarine surface area loss worldwide. Our field and numerical studies revealed that regardless of estuarine type, estuarine dams amplified the tidal range and reduced the tidal currents. The estuarine turbidity maximum moved seaward, and the suspended sediment concentration tended to decrease. While the morphologic changes depended on the estuarine type, the surficial sediment texture shifted to being muddier for all types. This work is one of the first to show the global extent of estuaries of an estuarine dam and their systematic effects on estuarine sedimentary processes.

How to cite: Lee, G., Jung, N., Figueroa, S., Dellapenna, T., and Chang, J.: Global distribution of estuarine dams and their sedimentological impact, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5015, https://doi.org/10.5194/egusphere-egu23-5015, 2023.

The world’s river deltas are increasingly vulnerable due to pressures from human activities and environmental change. In deltaic regions, the distribution of salinity controls the resourcing of fresh water for agriculture, aquaculture and human consumption; it also regulates the functioning of critical natural habitats. Excessive salinity can harm the sustainability of these delicate ecosystems and compromise the various anthropogenic activities taking place there. Currently, many deltas face the consequences of increased salinity due to sea level rise. Salt intrusion (i.e., upstream intrusion of the saltwater zone) is further exacerbated by shortages to freshwater availability due to changes in the hydrological cycle or upstream river diversions. Despite numerous insightful studies, there are still significant uncertainties on salinity’s spatio-temporal patterns response to changes in river flow and tidal range. In this study, an effort is done to fill this gap through idealized three-dimensional numerical modelling of a typical delta configuration. A series of simulations is carried out considering seasonal freshwater flow and tidal level variations. Model results demonstrated the existence of simple correlations and relationships describing the salinity field in a delta. In particular, salinity and river discharge are exponentially correlated through an equation that shows similarities to solutions of the one-dimensional advection-diffusion equation. The use of stream labelling methods (e.g., Strahler-Horton, width function) disclosed another correlation with salinity increasing as the channels’ order decreases.  In addition, small increases of the tidal amplitude in river-dominated or low tidal regime cases were found to have positive effects against salinization because of tide-induced mixing that can increase freshwater areas and volumes. Finally, results from simulations of different flow regimes indicated that it is possible to mitigate deltas’ salinization by water regulations and better use of existing resources instead of resorting to expensive and harmful for the environment technical solutions.

How to cite: Matsoukis, C., Amoudry, L., Bricheno, L., and Leonardi, N.: Investigating the impact of river flow and tidal level variations on river delta salinization through idealized numerical modelling, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16970, https://doi.org/10.5194/egusphere-egu23-16970, 2023.

Delta systems evolve as a function of interactions between hydroclimatic processes that occur at the watershed level, and coastal marine processes that reshape the coastline. The evolution of these environments is controlled by several factors, like climate, tectonics, and anthropization (by feedback on soils, vegetation, hydrosystems) yet rarely taken into account in models of evolution of sedimentary systems.

The Rhone delta has recorded the impact of climatic variations as well as the development and evolution of human societies during the Holocene period. This system has undergone a post-glacial evolution controlled by a global climatic warming punctuated by short periods of cooling, fluvial metamorphoses, and by a rapid marine transgression generated by the melting of the ice caps, which was followed by the initiation of the progradation of the delta from about 7000 BP, and which seems to accelerate during the Roman antiquity (Arnaud-Fassetta, 2002). The dynamics of the system was modified during the Little Ice Age (LIA, 1350-1850), under the combined effects of a climatic cooling that modified the dynamics of the system, and the increasing effect of anthropization forcing (land use, deforestation, damming, …). The evolution of hydroclimatic variations since the end of the LIA corresponds to a decrease in the frequency of floods and the overall decrease in rainfall, favoring the impact of human activities which became increasingly important until the 20^th century (canalization of the river, construction of dams...). The industrial revolution and mechanization led to a drastic increase in sediment flows in most major rivers, due to deforestation, deep destructuring of cultivated soils and the generalization of intensive farming (Fanget et al., 2013). In the 1950s, this signal is reversed with the proliferation of dams in many rivers, which generates a reduction in sediment load from upstream to downstream.

Sedimentological and chronostratigraphic studies of 17 coredrills complementing an existing dataset on the deltaic plain (Arnaud-Fassetta & Suc, 2015; Amorosi et al., 2013, Vella et al., 2005, 2008), as well as on the prodelta (Jouet, 2007; Fanget et al, 2012, 2014) enabled to the construction of well-constrained stratigraphic correlations, allowing to specify the stratigraphic architecture of the delta and the spatio-temporal evolution of the different lobes composing the Rhone deltaic edifice (lobes of St Ferréol, Ulmet, Peccaïs, Bras de Fer and then Roustan chronologically). The variation of sediment fluxes was evaluated for the different sequences of deltaic progradation phases. This calculation was made possible by the contribution of new dating of cores that helped at constraining the sequential evolution of the lobes. In addition, numerous geochemical data obtained by XRF are carried out on samples of these cores and make it possible to link the deposition of the various sedimentary lobes with the potential contribution of the various sub-watersheds of the Rhone. All these data highlight contrasting periods corresponding to the pre-LIA period (with an increasing impact of human activities on the landscape since the late Neolithic period), the LIA period, the post-LIA period, the industrial revolution and finally the “anthropocene".)

How to cite: Martinez, T., Deschamps, R., Jouet, G., Amorosi, A., Vella, C., Ducret, G., and Berger, J.-F.: Controlling factors on the stratigraphic architecture of the Rhône delta during Holocene, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3194, https://doi.org/10.5194/egusphere-egu23-3194, 2023.

Over the years, a relevant percentage of the population migrate towards coastal areas and nearby. In Spain, nowadays almost 40% of the population is settled close to the coast, and this value increases in summertime. Therefore, these areas have a great social, environmental and economic pressure. Besides their inherent value, both sea level rise and an increase in the frequency and intensity of extreme events are expected over the coming years induced by climate change. According to the last AR6 IPCC Report (2022), natural and anthropised coastal areas will still be at severe risk of erosion and flooding. Therefore, the understanding and modeling of the long-term morphodynamics of near-shore areas with some certainty is crucial for adaptation and mitigation.

Even though the study of coastal morphodynamics has evolved during the last decades, a great computational effort in modelling the effects of the different drivers is still required, particularly to analyze the effects of wave climate on near-shore morphodynamics. On account of the above-mentioned, different wave climate schematization techniques have been developed and applied during the last years: Synthetic Wave Events, SWE, Categorized Wave Classes, CWC, or Seasonal Averaged Wave Events, SAWE. Although with all these techniques shorter but morphodynamically equivalent wave climate time series are obtained, the storm chronology is not always preserved. In this research we aim to analyze the relative importance of maintaining (or not) the wave chronology in efficient morphodynamic simulations. For that, we will run the different existing methods in an idealised numerical model and will present a new type of wave schematization technique, called “Storm Preservation Schematization” (SPS) in which storm chronology is preserved and a variable morphological acceleration factor (morfac) is used, accelerating the morphodynamics changes only during the time intervals between extreme events. Eventually, lowering the computational effort in numerical models will lead to a better understanding of the present and future dynamics of coastal environments.

In order to get a more realistic geometry, the initial conditions used for the comparative simulations between schematization techniques are obtained after a one-year simulation with realistic climate information in an idealised bathymetry. Both the initial simulation and those for the comparative analysis are performed with the Delft3D model. Initial results after analyzing the final morphologies obtained with each methodology indicate that the new approach for wave schematization (SPS) provide more realistic results when compared to the existing methods, highlighting the importance of keeping the real duration of the storms. Detailed results will be presented at the congress.

How to cite: Aragón, M., Martín-Llanes, G., Zarzuelo, C., López-Ruiz, A., and Ortega-Sánchez, M.: The importance of wave chronology in wave schematization for morphodynamic modeling in coastal zones, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1620, https://doi.org/10.5194/egusphere-egu23-1620, 2023.

Cigu lagoon in Southwest Taiwan is susceptible to disappear due to sandbar migration and sedimentation issues over the past few decades. According to the Water Resources Agency in Taiwan, the sandbar has retreated more than 800 meters to the landward from 1975 to 2005. As a result, the Cigu lagoon has been shrinking from 10,000 to 1,350 hectares nowadays. In addition, various river and coastal management decisions in the last century have also contributed to the disruption of the natural sediment balance along the Cigu coast. A compounding consequence of these processes continuously occurs, changing the hydrodynamic characteristics and accelerating the siltation process of the lagoon.

A deeper understanding of the erosive and deposition processes at play in the Cigu lagoon is essential to inform current coastal management practices in the area. This study combined remote sensing and a 2-D hydrodynamic model to examine the sediment transport and siltation process in the Cigu lagoon. A remote sensing technique is conducted to complement the initial suspended sediment concentration (SSC) on the model. The results of this study indicate that tidal currents and wave forcings primarily influence the sediment transport and siltation process of the Cigu lagoon. The annual siltation of the Cigu lagoon is 0.82 cm, and this process mainly occurs during the winter season. The strong winter wave induces sediment mixing and suspension in the water column, which causes the SSC and sedimentation of Cigu higher than those in the summer.

In this particular case, lagoon siltation was also exacerbated by sediment from the sandbar. The overwash phenomenon swept a large amount of sediment from the sandbar to the lagoon. Moreover, based on our sediment budget analysis, about 0.1 million m³ of sediment in the Cigu sandbar is eroded every year, and some sediment is transported to the lagoon by tidal currents and wave actions. The study implies that many elements have contributed to the siltation of Cigu lagoon, and the whole coastal system management needs to be taken into consideration for managing lagoon siltation.

How to cite: Dhian, B. A. and Wang, H.-W.: Will Taiwan lose its lagoon? Effects of sandbar migration and sediment transport on lagoon siltation in Southwest Taiwan, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10452, https://doi.org/10.5194/egusphere-egu23-10452, 2023.

Coastal systems are among the most economically valuable and highly threatened systems on Earth. They provide a wide range of valuable ecosystem services but are severely threatened by climate changes and increasing human pressure. We consider and analyze the Venice Lagoon as a paradigmatic case representative of the coevolution of man and landscape, of natural processes and human agency. The history and fate of Venice Lagoon, the largest brackish waterbody in the Mediterranean, are tightly intertwined with those of the City of Venice. We show, through an interdisciplinary approach combining field observations, remote sensing, laboratory analyses, and mathematical modeling, that increasing anthropogenic pressure, coupled with the effects of natural processes exacerbated by climate changes, has led to an accelerated morphological deterioration of the lagoon and of the related ecosystem services. We also provide new insights on the short- and long-term consequences of coastal flooding prevention measures, such as storm-surge barriers, which are being widely adopted globally because of the accelerating rise in sea levels. From this point of view, the Venice and Venice Lagoon issues are becoming the new paradigm of the conflicts arising from the interactions among economy, society, and the environment, the three main pillars of sustainable development, furthermore providing an indication of what fate has in store for coastal cities and ecosystems of the future.

How to cite: D'Alpaos, A., Finotello, A., Tognin, D., Carniello, L., and Marani, M.: The Venice Lagoon foreshadows the fate of coastal systems under climate change and increasing human pressure., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10125, https://doi.org/10.5194/egusphere-egu23-10125, 2023.