GM6.10

EDI
The future of estuaries and deltas: natural processes and human interference

Deltas and estuaries are home to 7% of the world’s population but they are also hotspots for disasters. These riverine landforms face a wide range of challenges, now and in the future, including climatic changes (sea level rise, changing river discharge), biodiversity loss, subsidence, sediment mining, groundwater extraction, dredging and engineering measures (dams, embankments, sluices etc.). Deltas and estuaries lie at the interface of complex river, tidal and wave processes which create distinctive morphologies and environments. They provide the hinterland with protection from flooding and erosion but are also key resource areas for freshwater, ecology and sediment. Protecting delta regions and estuaries is therefore a key research area for science and policy. Understanding the functioning of delta and estuarine processes, including hydrodynamic processes, morphological development and the effects of human interference, is key for a sustainable future for these systems. To prepare for future changes it is crucial to identify the present state of these systems and learn from their past development. This session aims to bring together knowledge from multiple disciplines such as geomorphology, hydrology, ecology, social sciences and science policy to identify how deltas and estuaries change and what future societal challenges might arise along their shores. We particularly encourage early career researchers to submit to this session and welcome contributions from those working on estuary and delta management, future issues in estuaries and deltas, and process and system based science of estuaries and deltas.

Co-organized by HS13/NH5
Convener: Jana CoxECSECS | Co-conveners: Anne BaarECSECS, Lisanne Braat, Frances DunnECSECS, Iris Moeller
vPICO presentations
| Wed, 28 Apr, 09:00–10:30 (CEST)

Session assets

Session materials

vPICO presentations: Wed, 28 Apr

Chairperson: Jana Cox
09:00–09:05
09:05–09:07
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EGU21-967
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ECS
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Highlight
Jaap Nienhuis, Juan Paniagua-Arroyave, Frances Dunn, Sagy Cohen, and Torbjorn Tornqvist

Fluvial sediments have collectively formed about 900,000 km2 of deltaic land since Holocene sea-level rise slowed down. The rate at which deltas have retained fluvial sediment to build deltaic land, however, has varied greatly between different deltas. Here we quantify sediment retention in the delta topset and foreset for 3,556 deltas globally. We estimate retention from data on delta morphology and cross-sectional area, combined with WBMSed data on fluvial suspended sediment supply. Deltas, on average, retain 25±2% (standard error of the mean) of the fluvial sediment in their topset and 31±2% in their foreset. Because topset sediment retention reduces the sediment delivery to the river mouth, it sets up a feedback with processes that build delta morphology. Waves reduce topset sediment retention whereas tides increase it. Tide dominated deltas retain 61±24% on their topset, on average, compared to 21±3% and 24±2% for river- and wave-dominated deltas, respectively. Larger deltas trap more sediment, but not in comparison to their larger sediment loads, making them relatively inefficient sediment traps.

How to cite: Nienhuis, J., Paniagua-Arroyave, J., Dunn, F., Cohen, S., and Tornqvist, T.: Sediment retention in river deltas and feedbacks with delta morphology, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-967, https://doi.org/10.5194/egusphere-egu21-967, 2021.

09:07–09:09
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EGU21-1441
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ECS
Weilun Gao, Dongxue Li, Mawusi Amenuvor, Yao Tong, Dongdong Shao, and Baoshan Cui

Deltas are among the most populous areas and most productive ecosystems on Earth. Despite their critical importance for human society and coastal ecosystems, many of the world’s deltas are drowning due to substantial decrease in sediment supply, sea level rise, etc. Previous studies have demonstrated the effects of dam regulation on the hydrological regime and morphological evolution of river deltas. However, past attention was mostly paid to individual deltas or deltas at a global scale, while comparative studies on selected deltas are scarce in the literature. In this study, a comparative study on two wave-influenced deltas, namely, the Volta River Delta in Ghana and the Yellow River Delta in China, was conducted. The trend of change of the annual river discharge and sediment load of the two deltas before and after the construction of the major dams were analyzed, and the resultant effects on deltaic morphological evolution were also examined and compared between the two deltas. The results show that the average annual river discharge and sediment load and their inter-annual variation decreased significantly after the construction of major upstream dams for both deltas. However, presumably due to the differences in reservoir capacity and upstream location of the dams, the sediment load of the Volta River Delta decreased abruptly to <10% of the sediment load in the pre-dam period after the construction of the Akosombo Dam in 1964 and became stable afterwards, whereas the sediment load of the Yellow River Delta decreased substantially to ~10% of pre-dam level but in a more gradual stepwise manner since the 1950s. As a result, after the intense shoreline retreat in the 1960s, the delta area of the Volta River Delta appeared to adjust to the reduced yet stable sediment load and shift to a new quasi-equilibrium with minimal change (maximum 0.53%). On the contrary, the Yellow River Delta still kept prograding at the river mouth given the current sediment load. However, it is foreseeable that if the trend of sediment reduction persists, it may potentially turn net delta progradation to erosion and further into a new quasi-equilibrium like the Volta River Delta. Our study provides a new perspective for understanding the future evolution of the Yellow River Delta as well as other deltas around the world that share similar characteristics and forcing factors.

How to cite: Gao, W., Li, D., Amenuvor, M., Tong, Y., Shao, D., and Cui, B.: A Tale of Two Deltas: Comparative Study on the Effects of Dam Regulation on Deltaic Hydrological Regime and Morphological Evolution, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1441, https://doi.org/10.5194/egusphere-egu21-1441, 2021.

09:09–09:11
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EGU21-1639
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ECS
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Highlight
Davide Tognin, Andrea D'Alpaos, Marco Marani, and Luca Carniello

Coastal wetlands lie at the interface between submerged and emerged environments and therefore represent unique yet delicate ecosystems. Their existence, resulting from complex interactions between hydrodynamics and sediment dynamics, is challenged by increasing rates of sea-level rise, lowered fluvial sediment input as well as an increasing anthropogenic pressure. The future survival of these peculiar morphologies is becoming even more complicated, because of the construction and planning of coastal defence structures designed to protect urban areas from flooding. Important examples are the flood protection systems built to protect New Orleans (USA), the river Scheldt Estuary (The Netherlands) and Venice (Italy). In this context, understanding the physical processes on which coastal marshes are grounded and how engineering measures can alter them is of extreme importance in order to plan conservation interventions.

To understand marsh sedimentation dynamics in flood-regulated environments, we investigated through field observations and modelling the effect of the storm-surge barrier designed to protect the city of Venice, the so-called Mo.S.E. system, which has in fact become operational since October 2020.

Sedimentation measurements in different salt marshes of the Venice lagoon carried out in the period October 2018-October 2020 show that more than 70% of yearly sedimentation accumulates during storm-surge conditions, despite their short duration. Moreover, the sedimentation rate displays a highly non-linear increase with marsh inundation intensity, due to the interplay between higher water levels and greater suspended sediment concentration. Barrier operations during storm surges to avoid flooding of urban areas will reduce water levels and marsh inundation. Therefore, we computed sedimentation in a flood-regulated scenario for the same observation period, using the relation we obtained between tidal forcing and sedimentation rate. Our results show that some occasional closures during intense storm surges (70 hours/year on average) suffice to reduce the yearly sedimentation of the same order of magnitude of the relative sea-level rise rate experienced by the Venice lagoon during the last century (2.5 mm/y).

We conclude that storm-surge barrier operations can dangerously reduce salt-marsh vertical accretion rate, thus challenging wetland survival in face of increasing sea-level rise.

How to cite: Tognin, D., D'Alpaos, A., Marani, M., and Carniello, L.: Coastal flooding protection will change salt-marsh sedimentation dynamics, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1639, https://doi.org/10.5194/egusphere-egu21-1639, 2021.

09:11–09:13
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EGU21-3302
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ECS
Juan F. Paniagua-Arroyave, Jaap H. Nienhuis, and Frances E. Dunn

Riverine sediment yield changes by human-induced catchment alterations can have important implications for river delta morphology. Here, we assess the potential response of 99 tropical deltas along the Caribbean and Pacific coasts of Colombia to projected human land use intensifications by deforestation and river damming. We assess delta morphology through the balance of wave, tidal, and (modern and future) river sediment transport processes at their mouths. We find that most Colombian deltas along the Caribbean coast are wave-dominated, except for large catchments with high riverine sediment load, which are river-dominated. Most deltas are wave-river dominated along the Pacific coast, with few examples of river-tide and wave-tide dominance. We predict Colombian deltas to become more wave and tide-dominated under river damming scenarios. In contrast, deforestation scenarios suggested virtually no future morphological changes.

How to cite: Paniagua-Arroyave, J. F., Nienhuis, J. H., and Dunn, F. E.: Potential Morphologic Responses of Tropical River Deltas in Colombia to Future Sediment Supply Scenarios, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3302, https://doi.org/10.5194/egusphere-egu21-3302, 2021.

09:13–09:15
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EGU21-4441
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ECS
Junyu Tao, Peng Hu, Wei Li, and Zhiguo He

It is generally believed that sediment erosion and deposition can’t occur simultaneously, which is also reflected in the classical Partheniades-Krone formulas used to calculate erosion and deposition flux. In this study, the erosion and deposition fluxes of cohesive sediment are integrated in the tidal period respectively, and when they are equal, the corresponding suspended cohesive sediment concentration is called ‘tidal average saturated concentration of cohesive sediment’. Theoretical analysis of the factors affecting the saturated concentration indicates that a large erosion coefficient results in a high saturated concentration level. The corresponding critical erosion and deposition shear stresses (i.e., τe and τd) at saturated concentration have many possibilities. Therefore, it is understandable that good agreement of suspended sediment concentration between simulation and observation have been obtained by adjusting τe and τd in the previous numerical simulation calibration. According to the relative magnitude of τe and τd at saturated concentration, the erosion and deposition fluxes of cohesive sediment can be divided into four situations: weak erosion (i.e., τe  > τd), intense erosion (i.e., τe  < τd), intense deposition (i.e., τe  < τd), and weak deposition (i.e., τe > τd ). A two-dimensional numerical model is applied to calculate the temporal and spatial variation of the saturated concentration of cohesive sediment in the Yangtze Estuary. Simulation results shows the following findings. 1) The impact of the fraction of the kth size class in the surface (top) layer of bed material on erosion flux of non-uniform cohesive sediment is necessary to be considered. Otherwise, the calculated saturated concentration of cohesive sediment is greater than the measured. 2) The differences between saturated concentration and the field calculated/measured suspended sediment concentration can be applied to infer bed erosion/deposition characteristics to some extent, and compared it with the measured erosion/deposition result, which in turn verifies the values of  τe and τd in the model. This finding provides insights for the following research on transport and diffusion of cohesive sediment in estuary and coastal areas.

How to cite: Tao, J., Hu, P., Li, W., and He, Z.: Analysis of tidal average saturated suspended sediment concentration of cohesive sediment in the Yangtze Estuary, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4441, https://doi.org/10.5194/egusphere-egu21-4441, 2021.

09:15–09:17
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EGU21-5140
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ECS
Frances E. Dunn and Philip S. J. Minderhoud

As one of the largest deltas in the world, the Mekong delta is home to over 17 million people and supports internationally important agriculture. Recently deposited sediment compacts and causes subsidence in deltas, so they require regular sediment input to maintain elevation relative to sea level. These processes are complicated by human activities, which prevent sediment deposition indirectly through reducing fluvial sediment supply and directly through the construction of flood defence infrastructure on deltas, impeding floods which deliver sediment to the land. Additionally, anthropogenic activities increase the rate of subsidence through the extraction of groundwater and other land-use practices.

This research shows the potential for fluvial sediment delivery to compensate for sea-level rise and subsidence in the Mekong delta over the 21st century. We use detailed elevation data and subsidence scenarios in combination with regional sea-level rise and fluvial sediment flux projections to quantify the potential for maintaining elevation relative to sea level in the Mekong delta. We present four examples of localised sedimentation scenarios in specific areas, for which we quantified the potential effectiveness of fluvial sediment deposition for offsetting relative sea-level rise. The presented sediment-based adaptation strategies are complicated by existing land use, therefore a change in water and sediment management is required to effectively use natural resources and employ these adaptation methods. The presented approach could be an exemplar to assess sedimentation strategy feasibility in other delta systems worldwide that are under threat from sea-level rise.

How to cite: Dunn, F. E. and Minderhoud, P. S. J.: Feasibility of sedimentation strategies for the Mekong delta to counterbalance relative sea-level rise, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5140, https://doi.org/10.5194/egusphere-egu21-5140, 2021.

09:17–09:19
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EGU21-6964
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ECS
Yue Li, Peng Hu, and Ji Li

The Yangtze Estuary Deepwater Channel Project has brought great economic and social benefits since its completion, but the siltation problem is still worthy of attention. In order to investigate the mechanisms of fluid mud in the estuary and to study the influence of fluid mud on siltation in the Yangtze Estuary Deepwater Channel, a two-dimensional physically-enhanced two-layer flow model will be developed in this paper. The model includes two series of governing equations which are about environment fluid and fluid mud, respectively. The model is based on the unstructured grid, and the governing equations are discretized by the finite volume method, and the improved LTS/GMaTS technology is used to improve the computational efficiency. Firstly, an experiment that the fluid mud was flowing underwater along a gentle slope is reconstructed by the two-layer model. It shows the ability of the model to describe the simple movement of fluid mud. Secondly, the model is applied to Yangtze Estuary. Without the fluid mud layer, the model can be simplified as a tide-current model. The reliability of the tidal current and tide level is verified, and it means the model can describe the tide accurately. Based on this, the process of formation, transport, and break-down of fluid mud is simulated and its effect on the siltation in the Yangtze Estuary Deepwater Channel is estimated.

How to cite: Li, Y., Hu, P., and Li, J.: A study on the dynamic process of fluid mud and its effect on siltation in the Yangtze Estuary Deepwater Channel, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6964, https://doi.org/10.5194/egusphere-egu21-6964, 2021.

09:19–09:21
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EGU21-8290
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ECS
Jasper Leuven, Daan van Keulen, Jaap Nienhuis, Alberto Canestrelli, and Ton Hoitink

Channel beds in estuaries and deltas often exhibit a local depth maximum at a location close to the coast. There are two known causes of large-scale (i.e. >10 river widths along-channel) channel bed scours: width constriction and draw down during river discharge extremes, both creating a local flow acceleration. Here, we systematically investigate a potential third mechanism. We study the effect of tidal dominance on the equilibrium channel bed in estuaries with a 1D-morphodynamic model. In estuaries, a morphodynamic equibrium is reached when the net (seaward) transport matches the upstream supply along the entire reach. The residual (river) current and river-tide interactions create seaward transport. Herein, river-tide interactions represent the seaward advection of tide-induced suspended sediment by the river flow. Tidal asymmetry typically creates landward transport. The main reason for scour formation is the amplification of tidal flow through funnelling of tidal energy. Only for a scouring profile the drop in river induced current magnitude reduces the river-tide interaction term, so that the net sediment transport matches the upstream sediment transport. When tidal influence is relatively large, and when channel convergence is strong, a equilibrium is only obtained with a scouring profile. We propose a predictor dependent on the width convergence, quantified as SB, and on the ratio between the specific peak tidal discharge at the mouth and the specific river discharge at the landward boundary (qtide/qriver). Scours develop if (qtide/qriver)/SB exceeds 0.3. These results are independent of scale and allow the prediction of scour in estuaries under future changes.

How to cite: Leuven, J., van Keulen, D., Nienhuis, J., Canestrelli, A., and Hoitink, T.: Large-scale scour in response to tidal dominance in estuaries, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8290, https://doi.org/10.5194/egusphere-egu21-8290, 2021.

09:21–09:23
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EGU21-9173
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ECS
Flow and Stratification in a Bedrock Confined Estuary
(withdrawn)
Amanda Wild and Eva Kwoll
09:23–09:25
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EGU21-9498
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ECS
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Highlight
Tara Mahavadi, Elisabeth Rudolph, Rita Seiffert, and Norbert Winkel

Future mean sea level rise will influence tidal dynamics and storm surge events in estuaries. The bathymetry in estuaries and coastal areas will also be affected by mean sea level rise, since it is in a morphodynamic equilibrium with hydrodynamic forces. Tidal flats, which are an important component of coastal protection, will grow to a certain extent with mean sea level rise in case of sufficient sediment availability.

With the help of a highly resolved hydrodynamic-numerical model of the German Bight (North Sea), we analyse the potential influence of mean sea level rise and vertical growth of tidal flats on tidal dynamics and storm surge events in the Elbe estuary.

The results show an increase of tidal amplitude and storm surge water levels due to mean sea level rise. A bathymetric rise of tidal flats in the German Bight and the mouth of the Elbe estuary leads to a decrease in storm surge water level and tidal amplitude compared to the scenario with sole mean sea level rise without a change in bathymetry. Further analyses show, how geometric parameters of the Elbe estuary are changing due to mean sea level rise and tidal flat growth. These changes in geometry influence tidal dynamics and can therefore be an explanation for the observed changes in tidal amplitude and storm surge water levels.

These findings enable a better understanding of future changes in the Elbe estuary and support coastal managers in decision making processes concerning adaptation options to reduce the impacts of climate change.

How to cite: Mahavadi, T., Rudolph, E., Seiffert, R., and Winkel, N.: Effects of mean sea level rise and tidal flat growth on tides and storm surge events in the Elbe estuary, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9498, https://doi.org/10.5194/egusphere-egu21-9498, 2021.

09:25–09:27
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EGU21-13180
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ECS
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Highlight
Joey O'Dell, Jaap H. Nienhuis, Jana R. Cox, Douglas A. Edmonds, and Paolo Scussolini

Global flood modelling requires standardised global flood-protection levee datasets. Current datasets, however, are generally confined to territorial boundaries (national datasets) and are scarcely made public. Here we report on our effort to collect and standardise flood-protection levee data for river deltas from various sources to create a single, open source and FAIR-aligned global dynamic evolving river levee data environment (openDELvE).

openDELvE aggregates data from national databases (including the USACE National Levee Database, and the UK EA Asset Information Management System, amongst others) as well as data collected from reports, maps, and satellite imagery. We report primarily the land areas  that the levees have been designed to protect, and where additional data is available, the location of levees and unified attributes.  openDELvE currently contains 1601 mapped leveed area polygons distributed over 152 deltas, covering 28% of globally defined delta area. Out of the 152 deltas, which cover a total delta area of 239,043 km2, the levees registered in the database protect a land area of 42,342 km2. Additionally, more extensive data has been collected from a selection of freely accessible public national databases (mostly the UK and USA, and some of Australia) spanning 5,089 km of levees with additional unified attributes (e.g. levee height, crest width, construction material), and a semi-automated process is being used to extend and develop this layer.

The data is published aligned to FAIR-standards and is open-source, with an interactive viewing platform to supplement the data which is targeted for use in global river delta modelling and research. The viewing platform for the database incorporates a community-driven revision tool to encourage ongoing improvement and refinement of delta levee data, which can be extended to future projects as required. 

How to cite: O'Dell, J., Nienhuis, J. H., Cox, J. R., Edmonds, D. A., and Scussolini, P.: A global database of flood-protection levees on river deltas (openDELvE), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13180, https://doi.org/10.5194/egusphere-egu21-13180, 2021.

09:27–09:29
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EGU21-13640
Daniel Peters, Wendy Monk, and Donald Baird

The Peace-Athabasca Delta (PAD) in one of the largest (~6000 km2) freshwater deltaic ecosystem in the world.  This low relief, deltaic floodplain formed at the confluence of the Peace-Athabasca-Birch rivers the west end of Lake Athabasca in northwestern Canada.  Small changes in water level/depth have important implications for surface water connectivity and associated habitat quality The floodplains contain more than 1000 wetland-lake basins with varying degrees of connectivity to the main flow system.  Hydroperiod is influenced by occasional ice-jam and open-water inundations that recharge wetland basins.  This culturally important and biologically rich delta is a Ramsar Convention Wetland Site of International Importance, and is a key feature of the Wood Buffalo National Park (WBNP) that is listed as a UNESCO World Heritage Site.  The PAD ecosystem is influenced by contributing basin and local scale hydrological stressors from flow regulation (eg, hydroelectric dam, weirs), water and land use (eg, oil sands mining) and climate change.

Growing concern regarding increased cumulative effects on the delta led Indigenous Peoples petitioning UNESCO World Heritage Committee (WNC) to reassess the protection status of the park. The WBNP Action Plan was developed to address 17 UNESCO WHC recommendations to ensure maintenance of Outstanding Universal Value of the Park.  One key set of recommendations is to: 1) Conduct environmental flows assessments, to the highest international standard, in order to identify water flows needed to sustain the ecological functioning of the PAD under current and projected development and climate change; 2) Establish adequate baseline hydrological information for PAD assessments.

A significant scientific effort has been invested in the last four decades, particularly since 2010, in improving our understanding the relationship between streamflow, landscape controls and aquatic ecology in this cold-regions delta.  This information is key to assess historical and present states, learn from past development to inform planned development, and prepare for anticipated future hydro-ecological changes.  However, several key questions arise regarding what is the best approach to preparing for the future and managing such a complex system, what management options are possible within an environmental flow framework given known hydrological stressors, and what future ecosystem state does society want for the delta.  The goal of this presentation focused on the PAD is threefold:  i)  Provide an overview of major hydro-ecological research and water management;  ii)  Assess the potential applicability of riverine environmental flow frameworks to deltaic floodplain environments; and iii)  Explore the development of an environmental flow/water level framework and tools necessary to assess and manage changes to the aquatic ecology of this internationally important deltaic ecosystem.

How to cite: Peters, D., Monk, W., and Baird, D.: The Future of a Cold Regions Deltaic Ecosystem Influenced by Multiple Hydrological Stressors, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13640, https://doi.org/10.5194/egusphere-egu21-13640, 2021.

09:29–09:31
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EGU21-16281
Paolo Paron, Stephanie Duvail, Olivier Hamerlynck, Dominque Hervé, Dinis Juizo, Simon Mwansasu, Wanja Nyingi, and Laurent Robison

We present the output of a research combining field based, expert knowledge and remote sensing, based on Google Earth Engine, aimed at the identification of the rates of changes and pathways during the past 35 years, in four Western Indian Ocean River Catchments and Deltas: Tana River in Kenya, Rufiji River in Tanzania, Limpopo River in Mozambique and Betsiboka River in Madagascar. These findings are a set of preliminary results of the collaborative and multidisciplinary effort produced within the GDRI-Sud network DELTAS and as a follow-up of the West Indian Ocean Deltas Exchange and Research network (WIODER) project that brought together the National Museum of Kenya, , University of Dar Es Salaam in Tanzania, University Eduardo Mondlane in Mozambique, Centre National de Recherches sur l'Environnement in  Madagascar, University of Southampton in UK, IHE Delft in the Netherlands, Institut de Recherche pour le Développement in France, and International Development Research Centre in Canada and Kenya.

We highlight the similarities in the physical environment and, where possible, also in the socio-economic-political environments that are leading the current changes, potentially affecting resilience of the local population and their sustainable development.

We focused on the substantial changes in the following aspects: precipitation seasonality, flooding patterns and frequency, land cover, dry forest cover, mangrove cover, crop production, fish population, human population, human migration flow, frequency of human conflicts within the delta population.

The observed changes call for reflection given the IPCC projections in climate towards an aridification of the Southern Africa river basins and a wetter condition in the Eastern Africa region. Some signals of these climatic forecast are already recorded in both regions and will be explored in the DIDEM project.

How to cite: Paron, P., Duvail, S., Hamerlynck, O., Hervé, D., Juizo, D., Mwansasu, S., Nyingi, W., and Robison, L.: Pathways of change in the socio-shysical dynamics of the Western Indian Ocean deltas, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16281, https://doi.org/10.5194/egusphere-egu21-16281, 2021.

09:31–09:33
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EGU21-16435
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ECS
Reinier Schrijvershof, Bas van Maren, Bart Vermeulen, and Ton Hoitink

Intertidal areas disappear in deltas worldwide because of land reclamations. This greatly impacts delta morphology because the presence and physiological characteristics of intertidal areas determine the tidal regime and, as a result, residual sediment transport patterns in tidal basins. Understanding how the interaction between intertidal areas and channels in tidal basins influence morphodynamics is therefore important to predict morphological development and to assess the resilience of delta’s to changing boundary conditions.

In the Ems estuary (The Netherlands), the gradual embankment of a large intertidal embayment altered the planform and cross-sectional geometry of the estuary, leading to changes in the tidal regime and associated residual sediment transport patterns. As early as 1952, it was already suggested that these changes eventually caused a shift towards an alternative historical development of the geometric configuration of the channels; from a multiple to a single channel system.

This study shows through centennial-scale morphological modelling that the observed system shift can be hind-casted, while conserving model validity by comparison to the observed gross morphodynamics trends. The results indicate that the system shift is indeed driven by land reclamations. This provides a unique case to study the processes leading to the observed developments and evaluate the value of tidal-asymmetry based stability relationships to predict regime shifts in estuarine development.

How to cite: Schrijvershof, R., van Maren, B., Vermeulen, B., and Hoitink, T.: Intertidal floodplain controls on centennial-scale morphological channel development, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16435, https://doi.org/10.5194/egusphere-egu21-16435, 2021.

09:33–09:35
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EGU21-16444
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ECS
Amelia Paszkowski, Steven Goodbred Jr, Edoardo Borgomeo, M. Shah Alam Khan, and Jim W. Hall

The Ganges-Brahmaputra-Meghna (GBM) rivers deliver the greatest sediment flux to the world’s oceans, generating the Earth’s largest delta system, which is home to over 170 million people. Despite its scale and complexity, the GBM delta system remains a relatively under-researched region, with geomorphic dynamics often overlooked in studies of its vulnerability. A synthesis of these research efforts remains absent, resulting in most geomorphic studies being spatially, temporally, and topically fragmented. In this research, we therefore bind these studies together, providing a holistic, delta-wide account of the GBM’s prevailing dynamics and evolution, as well as identify key areas for future research. We built a sample of 427 peer-reviewed articles published from 1863 to 2020, and applied the Driver-Pressure-State-Impact-Response (DPSIR) framework to the geomorphic dynamics of the delta. We find that the delta has been responding to complex natural and anthropogenic perturbations in the form of subsidence, shifting river flows and sedimentation patterns. These processes subsequently impact on the extent and magnitude of flooding, result in losses to biodiversity, and most critically, severely disrupt local livelihoods. Amongst other key systemic gaps identified in this research, this study finds that (i) the GBM delta is typically assessed and modelled as a physical system with limited recognition of the dynamic interaction with human actions; and (ii) only 5% of studies assessed how the morphology of the delta may change in the future. Ultimately, this systematic review argues that although climate change and sea-level rise remain major concerns for the delta in the coming decades, multi-scale management and policy decisions have a more direct influence on the future geomorphic balance of the GBM delta.

How to cite: Paszkowski, A., Goodbred Jr, S., Borgomeo, E., Khan, M. S. A., and W. Hall, J.: Binding the Ganges-Brahmaputra-Meghna Braids: A review of geomorphic change in the world's largest delta, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16444, https://doi.org/10.5194/egusphere-egu21-16444, 2021.

09:35–10:30