E. Mosselman
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1
River management has been practiced in the Netherlands for centuries, with groynes traditionally playing a key role. However, groynes do not provide a comprehensive solution to all challenges associated with rivers (Mosselman et al., 2021). Therefore, longitudinal training walls were introduced. These are long, narrow walls constructed parallel to the riverbank that divide the river into a main channel and a side channel. At high discharges, longitudinal training walls improve flood safety, while at low discharges they enhance navigability (Osorio et al., 2020). Because separate longitudinal water level profiles develop in the two channels, water levels within a cross-section can be different. Due to the porous nature of the training wall, these differences generate lateral flow between the main and side channel. This research investigates the following research question: How does lateral exchange between a main and side channel through a porous longitudinal training wall affect river water depth? This is particularly relevant during low discharge conditions, when minimum navigational depth is critical and lateral discharge towards the side channel may further reduce water depth in the main channel.
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River management has been practiced in the Netherlands for centuries, with groynes traditionally playing a key role. However, groynes do not provide a comprehensive solution to all challenges associated with rivers (Mosselman et al., 2021). Therefore, longitudinal training walls were introduced. These are long, narrow walls constructed parallel to the riverbank that divide the river into a main channel and a side channel. At high discharges, longitudinal training walls improve flood safety, while at low discharges they enhance navigability (Osorio et al., 2020). Because separate longitudinal water level profiles develop in the two channels, water levels within a cross-section can be different. Due to the porous nature of the training wall, these differences generate lateral flow between the main and side channel. This research investigates the following research question: How does lateral exchange between a main and side channel through a porous longitudinal training wall affect river water depth? This is particularly relevant during low discharge conditions, when minimum navigational depth is critical and lateral discharge towards the side channel may further reduce water depth in the main channel.
Human interferences have set off a multitude of morphological responses of the lower Rhine in Germany and the Netherlands. We share insights from thirty years of studies on these responses in the Niederrhein below Xanten and the branches in the delta. Elementary analyses of the 1D Saint-Venant–Exner equations explain the downstream flattening and upstream steepening of the longitudinal bed profile due to retrogressive erosion in response to river training, bend cut-offs and sediment mining. Three reasons make a 2D approach necessary for modelling the seemingly 1D problem of large-scale morphological response: (i) transverse variations in bed sediment composition, (ii) sediment division at river bifurcations, and (iii) the possibility that non-erodible layers in bends cause either erosion or sedimentation of the longitudinal bed profile. The Pannerdense Kop and IJsselkop bifurcations are in a state of quasi-equilibrium, essentially unstable but developing slowly. Considerable spatiotemporal variations in the sediment composition of the riverbed surface pose a challenge to stabilizing the longitudinal bed profile by matching gradients in flow velocity to gradients in bed sediment composition. As these variations form a major knowledge gap, we recommend research on the state and dynamics of sediment size and layer structure in the upper metres of the riverbed.
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Human interferences have set off a multitude of morphological responses of the lower Rhine in Germany and the Netherlands. We share insights from thirty years of studies on these responses in the Niederrhein below Xanten and the branches in the delta. Elementary analyses of the 1D Saint-Venant–Exner equations explain the downstream flattening and upstream steepening of the longitudinal bed profile due to retrogressive erosion in response to river training, bend cut-offs and sediment mining. Three reasons make a 2D approach necessary for modelling the seemingly 1D problem of large-scale morphological response: (i) transverse variations in bed sediment composition, (ii) sediment division at river bifurcations, and (iii) the possibility that non-erodible layers in bends cause either erosion or sedimentation of the longitudinal bed profile. The Pannerdense Kop and IJsselkop bifurcations are in a state of quasi-equilibrium, essentially unstable but developing slowly. Considerable spatiotemporal variations in the sediment composition of the riverbed surface pose a challenge to stabilizing the longitudinal bed profile by matching gradients in flow velocity to gradients in bed sediment composition. As these variations form a major knowledge gap, we recommend research on the state and dynamics of sediment size and layer structure in the upper metres of the riverbed.
Journal article
(2025)
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Mohammad Bahrami-Yarahmadi, Roya Erick, Mahmood Shafai-Bejestan, Erik Mosselman
Bank-attached vanes (BAVs) are triangular vanes to protect the outer banks of river bends against erosion. However, their performance for higher or lower bankfull depth is uncertain. This study aims to validate the Flow3D numerical model, to study the effects of submergence and emergence of BAVs on flow patterns and bed shear stresses at h/H = 0.5, 1, 1.5 and 2 (h = flow depth, H = BAV height) and constant Froude number. The results showed that a recirculation cell, 1.046 times the structure’s length, developed behind the emerged BAV (h/H = 0.5), whereas no recirculation occurred behind the submerged BAV (h/H = 1, 1.5 and 2). Increasing the flow depth undermined the BAV’s effectiveness in reducing bed shear stress near the outer bank. The bed shear stress near the BAV’s tip at h/H = 0.5, 1, 1.5 and 2 was equivalent to 1.67, 1.45, 1.3 and 1.24 times the average bed shear stress upstream of the bend, respectively.
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Bank-attached vanes (BAVs) are triangular vanes to protect the outer banks of river bends against erosion. However, their performance for higher or lower bankfull depth is uncertain. This study aims to validate the Flow3D numerical model, to study the effects of submergence and emergence of BAVs on flow patterns and bed shear stresses at h/H = 0.5, 1, 1.5 and 2 (h = flow depth, H = BAV height) and constant Froude number. The results showed that a recirculation cell, 1.046 times the structure’s length, developed behind the emerged BAV (h/H = 0.5), whereas no recirculation occurred behind the submerged BAV (h/H = 1, 1.5 and 2). Increasing the flow depth undermined the BAV’s effectiveness in reducing bed shear stress near the outer bank. The bed shear stress near the BAV’s tip at h/H = 0.5, 1, 1.5 and 2 was equivalent to 1.67, 1.45, 1.3 and 1.24 times the average bed shear stress upstream of the bend, respectively.
The Brahmaputra-Jamuna River in the plains of Assam (India) and Bangladesh is characterised by high bank erosion rates, cycles of widening and narrowing of its braid belt, unidirectional braid belt migration, and avulsions. The objective of this paper is to share insights in sustainable stabilisation of this river that have evolved in the past 30 years. Main benefits of stabilisation are the stopping of bank erosion outside its braid belt, avoidance of the breaching of embankments, provision of navigation channels to ports and ferry landings, and provision of stable distributary offtakes for freshwater supply. Often land reclamation by narrowing the river appears as an additional target. The paper argues that this has at least three adverse effects: (i) rise of flood water levels and decrease of hydraulic robustness; (ii) decrease of morphological robustness; (iii) potential tipping over of the fluvial system from a river responding horizontally to changes towards a river that incises its bed and responds vertically to changes. The paper discusses socio-economic implications and gives recommendations for sustainable stabilisation.
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The Brahmaputra-Jamuna River in the plains of Assam (India) and Bangladesh is characterised by high bank erosion rates, cycles of widening and narrowing of its braid belt, unidirectional braid belt migration, and avulsions. The objective of this paper is to share insights in sustainable stabilisation of this river that have evolved in the past 30 years. Main benefits of stabilisation are the stopping of bank erosion outside its braid belt, avoidance of the breaching of embankments, provision of navigation channels to ports and ferry landings, and provision of stable distributary offtakes for freshwater supply. Often land reclamation by narrowing the river appears as an additional target. The paper argues that this has at least three adverse effects: (i) rise of flood water levels and decrease of hydraulic robustness; (ii) decrease of morphological robustness; (iii) potential tipping over of the fluvial system from a river responding horizontally to changes towards a river that incises its bed and responds vertically to changes. The paper discusses socio-economic implications and gives recommendations for sustainable stabilisation.
Braided rivers are the most dynamic type of rivers, with a rapid and intricate morphological evolution. A limited understanding and inadequate algorithm implementation of specific morphological processes limits the prediction capabilities of physics-based models. The design of structures, infrastructure, and other interventions is consequently hampered. In recent years artificial intelligence (AI) techniques rapidly gained popularity across different contexts. Additionally, the availability of satellite images increased. This research sets a novel attempt to predict the planform evolution of braided rivers by means of deep learning and satellite images. The Brahmaputra-Jamuna River, in India and Bangladesh, was selected as case study. A convolutional neural network (CNN) with U-Net architecture was developed. The model was trained with the Global Surface Water Dataset (GSWD). The goal of the model was to classify each pixel as either "Non-water" or "Water". Four images, representative of the same month over four consecutive years, were used as input. The fifth-year image represented the target. The model demonstrated good skills in predicting the planform development. Processes like the migration of meanders, the abandonment of channels, and the evolution of confluences and bifurcations were often well captured. However, a lack of temporal patterns was noticed. More complex phenomena, like the formation and shifting of channels, were never predicted. The total areas of erosion and deposition were constantly underpredicted. Metrics such as precision, recall, F1-score, and critical success index (CSI) were tracked. Overall, our model achieved a 5-6% total improvement of these metrics compared to the benchmark method for which no morphological change is assumed to occur. Our model could be useful as a preliminary tool for water management authorities in India and Bangladesh. It can support the prioritisation of bank protection measures in areas subject to erosion or land reclamation projects in areas subject to deposition and assist inland navigation. Given the inherent tendency of the model to underpredict erosion, caution is always advised. More research is required to improve the current model. Despite this, deep-learning modelling could become a potentially valuable field of research. Testing alternative model architectures, increasing the datasets size, and incorporating additional data, such as water levels or river discharge, are some of the proposed strategies to improve the model performance.
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Braided rivers are the most dynamic type of rivers, with a rapid and intricate morphological evolution. A limited understanding and inadequate algorithm implementation of specific morphological processes limits the prediction capabilities of physics-based models. The design of structures, infrastructure, and other interventions is consequently hampered. In recent years artificial intelligence (AI) techniques rapidly gained popularity across different contexts. Additionally, the availability of satellite images increased. This research sets a novel attempt to predict the planform evolution of braided rivers by means of deep learning and satellite images. The Brahmaputra-Jamuna River, in India and Bangladesh, was selected as case study. A convolutional neural network (CNN) with U-Net architecture was developed. The model was trained with the Global Surface Water Dataset (GSWD). The goal of the model was to classify each pixel as either "Non-water" or "Water". Four images, representative of the same month over four consecutive years, were used as input. The fifth-year image represented the target. The model demonstrated good skills in predicting the planform development. Processes like the migration of meanders, the abandonment of channels, and the evolution of confluences and bifurcations were often well captured. However, a lack of temporal patterns was noticed. More complex phenomena, like the formation and shifting of channels, were never predicted. The total areas of erosion and deposition were constantly underpredicted. Metrics such as precision, recall, F1-score, and critical success index (CSI) were tracked. Overall, our model achieved a 5-6% total improvement of these metrics compared to the benchmark method for which no morphological change is assumed to occur. Our model could be useful as a preliminary tool for water management authorities in India and Bangladesh. It can support the prioritisation of bank protection measures in areas subject to erosion or land reclamation projects in areas subject to deposition and assist inland navigation. Given the inherent tendency of the model to underpredict erosion, caution is always advised. More research is required to improve the current model. Despite this, deep-learning modelling could become a potentially valuable field of research. Testing alternative model architectures, increasing the datasets size, and incorporating additional data, such as water levels or river discharge, are some of the proposed strategies to improve the model performance.
Millennia of engineering have shaped the rivers in the Netherlands in response to flood events, wars, and socio-economic developments. Continuous adaptation mostly occurred ad hoc and was reactive without integrated long-term planning. Anticipating adaptive management is only a recent development. It uses scenarios of future developments but also acknowledges deep uncertainty. In hindsight, for instance, nobody foresaw the rapid French invasion in 1672 by wading through one of the Rhine branches, which was decisive for relocating the main Rhine bifurcation from Schenkenschans to Pannerden, and for stabilizing its distribution of discharges [1]. Adaptive river management seeks to maintain or improve rivers in ways that do not cause regrets, avoid lock-ins, and prevent adverse effects in the long run
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Millennia of engineering have shaped the rivers in the Netherlands in response to flood events, wars, and socio-economic developments. Continuous adaptation mostly occurred ad hoc and was reactive without integrated long-term planning. Anticipating adaptive management is only a recent development. It uses scenarios of future developments but also acknowledges deep uncertainty. In hindsight, for instance, nobody foresaw the rapid French invasion in 1672 by wading through one of the Rhine branches, which was decisive for relocating the main Rhine bifurcation from Schenkenschans to Pannerden, and for stabilizing its distribution of discharges [1]. Adaptive river management seeks to maintain or improve rivers in ways that do not cause regrets, avoid lock-ins, and prevent adverse effects in the long run
Braided rivers are the most dynamic type of rivers, with a rapid and intricate morphological evolution (Stecca et al., 2019). Being able to predict where and how rivers evolve is crucial for supporting spatial-related decisionmaking processes in the vicinity of these rivers. However, a limited understanding and inadequate algorithm implementation of specific morphological processes limits the prediction capabilities of physics-based models (Jagers, 2003; Siviglia and Crosato, 2016). The design of structures, infrastructure, and other interventions is consequently hampered at the expenses of the popoulation safety. In recent years artificial intelligence techniques rapidly gained popularity across different contexts (Blake et al., 2021) and the availability of satellite images increased. This research sets a novel attempt to predict the planform evolution of braided rivers by means of a deeplearning algorithm and using satellite images. The Brahmaputra-Jamuna River, in India and Bangladesh, was selected as case study (Best et al., 2022).
...
Braided rivers are the most dynamic type of rivers, with a rapid and intricate morphological evolution (Stecca et al., 2019). Being able to predict where and how rivers evolve is crucial for supporting spatial-related decisionmaking processes in the vicinity of these rivers. However, a limited understanding and inadequate algorithm implementation of specific morphological processes limits the prediction capabilities of physics-based models (Jagers, 2003; Siviglia and Crosato, 2016). The design of structures, infrastructure, and other interventions is consequently hampered at the expenses of the popoulation safety. In recent years artificial intelligence techniques rapidly gained popularity across different contexts (Blake et al., 2021) and the availability of satellite images increased. This research sets a novel attempt to predict the planform evolution of braided rivers by means of a deeplearning algorithm and using satellite images. The Brahmaputra-Jamuna River, in India and Bangladesh, was selected as case study (Best et al., 2022).
Journal article
(2025)
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H.J. Barneveld, R. M. Frings, R.P. van Denderen, J.S. de Jong, J.G.W. Beemster, L.A. Melsen, A.J.F. Hoitink, E. Mosselman, J. G. Venditti, M. G. Kleinhans, A. Blom, R.M.J. Schielen, W.H.J. Toonen, D. Meijer, A.J. Paarlberg
Climate change is expected to increase the frequency and magnitude of river floods
1. Floods not only cause damage by inundation and loss of life
2,3 but also jeopardize infrastructure because of bank failure and riverbed erosion processes that are poorly understood. Common flood safety programmes include dyke reinforcement and river widening
4, 5, 6, 7, 8–9. The 2021 flood in the Meuse Basin caused 43 fatalities and billions of dollars of damage to infrastructure
10. Here, on the basis of analysis of the Meuse flood, we show how uneven widening of the river and heterogeneity of sediment deposits under the river can cause massive erosion. A recent flood safety programme widened the river
11, but created bottlenecks where widening was either prevented by infrastructure or not yet implemented. Riverbed erosion was exacerbated by tectonic uplift that had produced a thin top gravel layer above fine-grained sediment. Greatly enhanced flow velocities produced underwater dunes with troughs that broke through the gravel armour in the bottlenecks, exposing easily erodible sands, resulting in extreme scour holes, one more than 15 m deep. Our investigation highlights the challenges of re-engineering rivers in the face of climate change, increased flood risks and competition for river widening space, and calls for a better understanding of the subsurface.
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Climate change is expected to increase the frequency and magnitude of river floods 1. Floods not only cause damage by inundation and loss of life 2,3 but also jeopardize infrastructure because of bank failure and riverbed erosion processes that are poorly understood. Common flood safety programmes include dyke reinforcement and river widening 4, 5, 6, 7, 8–9. The 2021 flood in the Meuse Basin caused 43 fatalities and billions of dollars of damage to infrastructure 10. Here, on the basis of analysis of the Meuse flood, we show how uneven widening of the river and heterogeneity of sediment deposits under the river can cause massive erosion. A recent flood safety programme widened the river 11, but created bottlenecks where widening was either prevented by infrastructure or not yet implemented. Riverbed erosion was exacerbated by tectonic uplift that had produced a thin top gravel layer above fine-grained sediment. Greatly enhanced flow velocities produced underwater dunes with troughs that broke through the gravel armour in the bottlenecks, exposing easily erodible sands, resulting in extreme scour holes, one more than 15 m deep. Our investigation highlights the challenges of re-engineering rivers in the face of climate change, increased flood risks and competition for river widening space, and calls for a better understanding of the subsurface.
Submerged vanes are an effective approach to sediment management in river systems. Nowadays, submerged vanes are increasingly utilized in contemporary river engineering due to their convenient and cost-effective installation, which distinguishes them from traditional approaches. However, this structure induces localized scour, which can potentially destabilize and compromise its integrity. The performance and effectiveness of a submerged vane in controlling scour and managing sediment depends on its shape and dimensions. The primary aim of this study is to refine the design of submerged vanes to assess the maximum scour depth in their vicinity and changes in bed morphology downstream of the vane. We carried out 95 experimental runs in clear-water conditions to investigate the influence of vane height, bevel angle, angle of flow attack, and flow regime on the maximum scour depth in the vicinity and downstream of the vane. Results show that the maximum scour depth increases with the increase in the angle of attack, vane height-to-depth ratio, and densimetric Froude number. The depth of scour around the vane and downstream in the channel decreases as the bevel angle increases. We propose empirical equations for calculating the maximum scour depth near the vane and downstream at equilibrium condition. The densimetric Froude number of the flow and the angle of flow attack are found to have the largest influence on maximum scour depth and downstream extension. The findings indicate that the bevel shape is effective method to reduces the maximum scour depth around the vane.
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Submerged vanes are an effective approach to sediment management in river systems. Nowadays, submerged vanes are increasingly utilized in contemporary river engineering due to their convenient and cost-effective installation, which distinguishes them from traditional approaches. However, this structure induces localized scour, which can potentially destabilize and compromise its integrity. The performance and effectiveness of a submerged vane in controlling scour and managing sediment depends on its shape and dimensions. The primary aim of this study is to refine the design of submerged vanes to assess the maximum scour depth in their vicinity and changes in bed morphology downstream of the vane. We carried out 95 experimental runs in clear-water conditions to investigate the influence of vane height, bevel angle, angle of flow attack, and flow regime on the maximum scour depth in the vicinity and downstream of the vane. Results show that the maximum scour depth increases with the increase in the angle of attack, vane height-to-depth ratio, and densimetric Froude number. The depth of scour around the vane and downstream in the channel decreases as the bevel angle increases. We propose empirical equations for calculating the maximum scour depth near the vane and downstream at equilibrium condition. The densimetric Froude number of the flow and the angle of flow attack are found to have the largest influence on maximum scour depth and downstream extension. The findings indicate that the bevel shape is effective method to reduces the maximum scour depth around the vane.
PIANC Working Group 236
Sustainable Management of the Navigability of Natural Rivers
The PIANC InCom/Envicom Working Group 236 was established in early 2021 to develop PIANC guidelines for improving navigability conditions on natural or quasi-natural rivers, while maintaining morphological processes, river form, and function. A natural river system exhibits two important characteristics – 1) unregulated hydrology and 2) unconstrained morphology. The key objectives of the WG236 – Sustainable Management of the Navigability of Natural Rivers – include: 1) development of guidelines to improve and maintain the navigability in natural rivers; 2) assess the sustainability of river training works designed to improve the navigability; 3) assess the sustainability of dynamic river management (monitoring and shifting of navigation aids to adapt the navigation channel to the river dynamics); 4) highlight the technical, operational, economic and environmental considerations for navigation in free-flowing rivers compared to that in regulated rivers and canals; and 5) improve the understanding of the physical processes in natural rivers, developed with or without river training works. The developed guidance includes a planning framework for developing a navigability improvement masterplan for a natural river system, and the integrated and adaptive management strategies that can be applied at a system scale. Specific interventions and measures have been identified that are analysed to meet the dual goals of maintaining morphological river function and improving navigability conditions. These measures include dynamic charting; morphological dredging and disposal management; Temporary, Adaptable, and Flexible Training Structures (TAFTS); riverbed armouring and sediment nourishment; rock excavation; meander cutoffs and oxbow development; localized traditional river training structures; and channel closure structures. The impacts and strategies for mitigating impacts associated with some of the measures are analysed and discussed. Finally, the continual monitoring, management, and operational tools available for improving navigability in a morphologically active river system are presented. ...
The PIANC InCom/Envicom Working Group 236 was established in early 2021 to develop PIANC guidelines for improving navigability conditions on natural or quasi-natural rivers, while maintaining morphological processes, river form, and function. A natural river system exhibits two important characteristics – 1) unregulated hydrology and 2) unconstrained morphology. The key objectives of the WG236 – Sustainable Management of the Navigability of Natural Rivers – include: 1) development of guidelines to improve and maintain the navigability in natural rivers; 2) assess the sustainability of river training works designed to improve the navigability; 3) assess the sustainability of dynamic river management (monitoring and shifting of navigation aids to adapt the navigation channel to the river dynamics); 4) highlight the technical, operational, economic and environmental considerations for navigation in free-flowing rivers compared to that in regulated rivers and canals; and 5) improve the understanding of the physical processes in natural rivers, developed with or without river training works. The developed guidance includes a planning framework for developing a navigability improvement masterplan for a natural river system, and the integrated and adaptive management strategies that can be applied at a system scale. Specific interventions and measures have been identified that are analysed to meet the dual goals of maintaining morphological river function and improving navigability conditions. These measures include dynamic charting; morphological dredging and disposal management; Temporary, Adaptable, and Flexible Training Structures (TAFTS); riverbed armouring and sediment nourishment; rock excavation; meander cutoffs and oxbow development; localized traditional river training structures; and channel closure structures. The impacts and strategies for mitigating impacts associated with some of the measures are analysed and discussed. Finally, the continual monitoring, management, and operational tools available for improving navigability in a morphologically active river system are presented.
En el presente trabajo analizamos los procesos morfodinámicos actuantes en un tramo del mega río Amazonas, el análisis se enfoca en cinco (5) estructuras anastomosadas en vecindad de las ciudades de Leticia en Colombia y Tabatinga en Brasil. Para la detección de cambios hemos usado la herramienta Google Earth Engine (GEE) y el código en JavaScript Mapping River Change desarrollado por Ramadhan, encontrando las trayectorias de migración del río entre los años 1990 y 2020, tres décadas marcadas por dos grandes eventos de caudales máximos en la amazonia (1999 y 2012). Por otro lado, las imágenes disponibles en el Timelapse de Google Earth Engine (GEE) han permitido entender la trayectoria evolutiva del meandro al final del tramo de estudio (curva La Alegría), el cual se ha transformado en una estructura anastomosada. Concluimos que la herramienta Google Earth Engine (GEE) permite análisis rápidos y de bajo costo para entender los procesos morfodinámicos actuantes en mega ríos tropicales y que combinada con métodos tradicionales es replicable para otros casos de estudio.
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En el presente trabajo analizamos los procesos morfodinámicos actuantes en un tramo del mega río Amazonas, el análisis se enfoca en cinco (5) estructuras anastomosadas en vecindad de las ciudades de Leticia en Colombia y Tabatinga en Brasil. Para la detección de cambios hemos usado la herramienta Google Earth Engine (GEE) y el código en JavaScript Mapping River Change desarrollado por Ramadhan, encontrando las trayectorias de migración del río entre los años 1990 y 2020, tres décadas marcadas por dos grandes eventos de caudales máximos en la amazonia (1999 y 2012). Por otro lado, las imágenes disponibles en el Timelapse de Google Earth Engine (GEE) han permitido entender la trayectoria evolutiva del meandro al final del tramo de estudio (curva La Alegría), el cual se ha transformado en una estructura anastomosada. Concluimos que la herramienta Google Earth Engine (GEE) permite análisis rápidos y de bajo costo para entender los procesos morfodinámicos actuantes en mega ríos tropicales y que combinada con métodos tradicionales es replicable para otros casos de estudio.
Journal article
(2024)
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Niels W. P. Brevé, Debora A. J. van Dieren, Marc Weeber, Erik Mosselman, Leopold A. J. Nagelkerke, Albertinka J. Murk, Anthonie D. Buijse
Information about reproductive habitat and migration pathways is of paramount importance to restore migratory fish species. This study assesses the availability of spawning and nursery habitats for the European sturgeon (Acipenser sturio) in the delta and lower Rhine (covering over 350 river kilometres) as part of a larger feasibility assessment for a future restoration of this critically endangered species. The general approach has three steps: (1) the identification of the species' specific habitat requirements, based on a systematic literature review; (2) the collection and preprocessing of data from two countries, including the 1D and 2D modelling of water depths and flow velocities; and (3) GIS-based mapping of spawning and nursery habitat. Based on a HSI score of 1, we identify a total of 0.75 km2 as minimal spawning habitat, potentially suitable for approximately 2500 female European sturgeons (one spawning site would use ~300 m2). This is sufficient, as currently, only an estimated maximum number of 750 adults exist. Suitable spawning habitat is mainly located in the German state of North Rhine-Westphalia, whereas suitable nursery habitat is mainly located in the Netherlands. The availability is, however, significantly reduced by coastal infrastructure (damming) and inland navigation. The insights gained can be used to assess the current suitability of the river Rhine for the species' reintroduction and to identify opportunities for habitat restoration and protection for various life stages. The outcomes thus play an essential role in the conservation of the species. In addition, the modelling approach developed could be applied to other northwestern European rivers. This broader application would allow intercomparison and support decisions about which rivers are best suited for future reintroduction of the critically endangered European sturgeon.
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Information about reproductive habitat and migration pathways is of paramount importance to restore migratory fish species. This study assesses the availability of spawning and nursery habitats for the European sturgeon (Acipenser sturio) in the delta and lower Rhine (covering over 350 river kilometres) as part of a larger feasibility assessment for a future restoration of this critically endangered species. The general approach has three steps: (1) the identification of the species' specific habitat requirements, based on a systematic literature review; (2) the collection and preprocessing of data from two countries, including the 1D and 2D modelling of water depths and flow velocities; and (3) GIS-based mapping of spawning and nursery habitat. Based on a HSI score of 1, we identify a total of 0.75 km2 as minimal spawning habitat, potentially suitable for approximately 2500 female European sturgeons (one spawning site would use ~300 m2). This is sufficient, as currently, only an estimated maximum number of 750 adults exist. Suitable spawning habitat is mainly located in the German state of North Rhine-Westphalia, whereas suitable nursery habitat is mainly located in the Netherlands. The availability is, however, significantly reduced by coastal infrastructure (damming) and inland navigation. The insights gained can be used to assess the current suitability of the river Rhine for the species' reintroduction and to identify opportunities for habitat restoration and protection for various life stages. The outcomes thus play an essential role in the conservation of the species. In addition, the modelling approach developed could be applied to other northwestern European rivers. This broader application would allow intercomparison and support decisions about which rivers are best suited for future reintroduction of the critically endangered European sturgeon.
Effects of urbanization and deforestation on flooding
Case study of Cap-Haïtien City, Haiti
Cap-Haïtien, the second largest city in Haiti, is highly vulnerable to earthquakes, landslides, and flooding. The rapid pace of urbanization and deforestation has exacerbated the risk of flooding, resulting in disasters in November 2012, 2016, and 2022. This study aims to assess the impact of urbanization and deforestation on river flooding in Cap-Haïtien by applying the hydrological model Soil Water Assessment Tool (SWAT) and the hydrodynamic model Sobek-Rural. We examined the current situation and a scenario of future urbanization and deforestation. Urbanization and deforestation are found to play a pivotal role in the production and deposition of sediment along the lower Haut-du-Cap River reaches. The existing hydraulic capacity of the river and its drainage system cannot handle the estimated peak flows. The mountain ravines west of the city are found to be the primary source of sediment-laden flash floods. We recommend retention basins, drainage extensions, and pragmatic public policies to mitigate flood risk. Comprehensive strategies are needed to address the detrimental effects of urbanization and deforestation on flooding in Cap-Haïtien and similar regions where a lack of water governance has worsened the flooding alongside urbanization and deforestation. We generalize our experiences from Cap-Haïtien into a broader framework for data-scarce areas.
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Cap-Haïtien, the second largest city in Haiti, is highly vulnerable to earthquakes, landslides, and flooding. The rapid pace of urbanization and deforestation has exacerbated the risk of flooding, resulting in disasters in November 2012, 2016, and 2022. This study aims to assess the impact of urbanization and deforestation on river flooding in Cap-Haïtien by applying the hydrological model Soil Water Assessment Tool (SWAT) and the hydrodynamic model Sobek-Rural. We examined the current situation and a scenario of future urbanization and deforestation. Urbanization and deforestation are found to play a pivotal role in the production and deposition of sediment along the lower Haut-du-Cap River reaches. The existing hydraulic capacity of the river and its drainage system cannot handle the estimated peak flows. The mountain ravines west of the city are found to be the primary source of sediment-laden flash floods. We recommend retention basins, drainage extensions, and pragmatic public policies to mitigate flood risk. Comprehensive strategies are needed to address the detrimental effects of urbanization and deforestation on flooding in Cap-Haïtien and similar regions where a lack of water governance has worsened the flooding alongside urbanization and deforestation. We generalize our experiences from Cap-Haïtien into a broader framework for data-scarce areas.
Sustainable river management often requires long-term morphological simulations. As the future is unknown, uncertainty needs to be accounted for, which may require probabilistic simulations covering a large parameter domain. Even for one-dimensional models, simulation times can be long. One of the acceleration strategies is simplification of models by neglecting terms in the governing hydrodynamic equations. Examples are the quasi-steady model and the diffusive wave model, both widely used by scientists and practitioners. Here, we establish under which conditions these simplified models are accurate. Based on results of linear stability analyses of the St. Venant-Exner equations, we assess migration celerities and damping of infinitesimal, but long riverbed perturbations. We did this for the full dynamic model, that is, no terms neglected, as well as for the simplified models. The accuracy of the simplified models was obtained from comparison between the characteristics of the riverbed perturbations for simplified models and the full dynamic model. We executed a spatial-mode and a temporal-mode linear analysis and compared the results with numerical modeling results for the full dynamic and simplified models, for very small and large bed waves. The numerical results match best with the temporal-mode linear analysis. We show that the quasi-steady model is highly accurate for Froude numbers up to 0.7, probably even for long river reaches with large flood wave damping. Although the diffusive wave model accurately predicts flood wave migration and damping, key morphological metrics deviate more than 5% (10%) from the full dynamic model when Froude numbers exceed 0.2 (0.3).
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Sustainable river management often requires long-term morphological simulations. As the future is unknown, uncertainty needs to be accounted for, which may require probabilistic simulations covering a large parameter domain. Even for one-dimensional models, simulation times can be long. One of the acceleration strategies is simplification of models by neglecting terms in the governing hydrodynamic equations. Examples are the quasi-steady model and the diffusive wave model, both widely used by scientists and practitioners. Here, we establish under which conditions these simplified models are accurate. Based on results of linear stability analyses of the St. Venant-Exner equations, we assess migration celerities and damping of infinitesimal, but long riverbed perturbations. We did this for the full dynamic model, that is, no terms neglected, as well as for the simplified models. The accuracy of the simplified models was obtained from comparison between the characteristics of the riverbed perturbations for simplified models and the full dynamic model. We executed a spatial-mode and a temporal-mode linear analysis and compared the results with numerical modeling results for the full dynamic and simplified models, for very small and large bed waves. The numerical results match best with the temporal-mode linear analysis. We show that the quasi-steady model is highly accurate for Froude numbers up to 0.7, probably even for long river reaches with large flood wave damping. Although the diffusive wave model accurately predicts flood wave migration and damping, key morphological metrics deviate more than 5% (10%) from the full dynamic model when Froude numbers exceed 0.2 (0.3).
The hydraulic resistance of groynes is an important factor in the determination of design flood water levels on rivers and the assessment of how much these levels are lowered by modifying the groynes. In standard one- or two-dimensional numerical hydrodynamic models for flood risk management, groynes are commonly represented as subgrid features with a local energy loss according to a weir formula. We tested this representation by using a two-dimensional horizontal mesh at various groyne submergence degrees by comparing the results with those of flume experiments. We also compared the results with simulations using different 2D and 3D approaches on finer grids that incorporate groynes in the bed topography. In one of the two tested 3D models, complete Reynolds-averaged Navier-Stokes equations were solved. The second tested 3D model was constructed simpler by assuming hydrostatic pressure distribution in the vertical direction. We employed Delft3D software in construction and execution of all models. One of the 3D models did predict the hydraulic resistance at low submergence better than the standard model, but it slightly underestimated the resistance at higher submergences. Despite differences in flow characteristics, weirs and groynes were found to produce similar flow resistances for the same height and boundary conditions. Simulations of groyne modifications showed that hydraulic resistance decreased nonlinearly with groyne lowering and streamlining.
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The hydraulic resistance of groynes is an important factor in the determination of design flood water levels on rivers and the assessment of how much these levels are lowered by modifying the groynes. In standard one- or two-dimensional numerical hydrodynamic models for flood risk management, groynes are commonly represented as subgrid features with a local energy loss according to a weir formula. We tested this representation by using a two-dimensional horizontal mesh at various groyne submergence degrees by comparing the results with those of flume experiments. We also compared the results with simulations using different 2D and 3D approaches on finer grids that incorporate groynes in the bed topography. In one of the two tested 3D models, complete Reynolds-averaged Navier-Stokes equations were solved. The second tested 3D model was constructed simpler by assuming hydrostatic pressure distribution in the vertical direction. We employed Delft3D software in construction and execution of all models. One of the 3D models did predict the hydraulic resistance at low submergence better than the standard model, but it slightly underestimated the resistance at higher submergences. Despite differences in flow characteristics, weirs and groynes were found to produce similar flow resistances for the same height and boundary conditions. Simulations of groyne modifications showed that hydraulic resistance decreased nonlinearly with groyne lowering and streamlining.
Sustainable river management often requires long-term morphological simulations. As the future is unknown, uncertainty needs to be accounted for, which may require probabilistic simulations covering a large parameter domain. Even for one-dimensional models, simulation times can be long. One of the acceleration strategies is simplification of models by neglecting terms in the governing hydrodynamic equations. Examples are the quasi-steady model and the diffusive wave model, both widely used by scientists and practitioners. We established under which conditions these simplified models are accurate.
Based on results of linear stability analyses of the St. Venant-Exner equations, we assessed migration celerities and damping of infinitesimal, but long riverbed perturbations. We did this for the full dynamic model, i.e. no terms neglected, as well as for the simplified models. The accuracy of the simplified models was obtained from comparison between the characteristics of the riverbed perturbations for simplified models and the full dynamic model.
We executed a spatial-mode and a temporal-mode linear analysis and compared the results with numerical modelling results for the full dynamic and simplified models, for very small and large bed waves. The numerical results match best with the temporal-mode linear analysis. We show that the quasi-steady model is highly accurate for Froude numbers up to 0.7, probably even for long river reaches with large flood wave damping. Although the diffusive wave model accurately predicts flood wave migration and damping, key morphological metrics deviate more than 5% (10%) from the full dynamic model when Froude numbers exceed 0.2 (0.3). ...
Based on results of linear stability analyses of the St. Venant-Exner equations, we assessed migration celerities and damping of infinitesimal, but long riverbed perturbations. We did this for the full dynamic model, i.e. no terms neglected, as well as for the simplified models. The accuracy of the simplified models was obtained from comparison between the characteristics of the riverbed perturbations for simplified models and the full dynamic model.
We executed a spatial-mode and a temporal-mode linear analysis and compared the results with numerical modelling results for the full dynamic and simplified models, for very small and large bed waves. The numerical results match best with the temporal-mode linear analysis. We show that the quasi-steady model is highly accurate for Froude numbers up to 0.7, probably even for long river reaches with large flood wave damping. Although the diffusive wave model accurately predicts flood wave migration and damping, key morphological metrics deviate more than 5% (10%) from the full dynamic model when Froude numbers exceed 0.2 (0.3). ...
Sustainable river management often requires long-term morphological simulations. As the future is unknown, uncertainty needs to be accounted for, which may require probabilistic simulations covering a large parameter domain. Even for one-dimensional models, simulation times can be long. One of the acceleration strategies is simplification of models by neglecting terms in the governing hydrodynamic equations. Examples are the quasi-steady model and the diffusive wave model, both widely used by scientists and practitioners. We established under which conditions these simplified models are accurate.
Based on results of linear stability analyses of the St. Venant-Exner equations, we assessed migration celerities and damping of infinitesimal, but long riverbed perturbations. We did this for the full dynamic model, i.e. no terms neglected, as well as for the simplified models. The accuracy of the simplified models was obtained from comparison between the characteristics of the riverbed perturbations for simplified models and the full dynamic model.
We executed a spatial-mode and a temporal-mode linear analysis and compared the results with numerical modelling results for the full dynamic and simplified models, for very small and large bed waves. The numerical results match best with the temporal-mode linear analysis. We show that the quasi-steady model is highly accurate for Froude numbers up to 0.7, probably even for long river reaches with large flood wave damping. Although the diffusive wave model accurately predicts flood wave migration and damping, key morphological metrics deviate more than 5% (10%) from the full dynamic model when Froude numbers exceed 0.2 (0.3).
Based on results of linear stability analyses of the St. Venant-Exner equations, we assessed migration celerities and damping of infinitesimal, but long riverbed perturbations. We did this for the full dynamic model, i.e. no terms neglected, as well as for the simplified models. The accuracy of the simplified models was obtained from comparison between the characteristics of the riverbed perturbations for simplified models and the full dynamic model.
We executed a spatial-mode and a temporal-mode linear analysis and compared the results with numerical modelling results for the full dynamic and simplified models, for very small and large bed waves. The numerical results match best with the temporal-mode linear analysis. We show that the quasi-steady model is highly accurate for Froude numbers up to 0.7, probably even for long river reaches with large flood wave damping. Although the diffusive wave model accurately predicts flood wave migration and damping, key morphological metrics deviate more than 5% (10%) from the full dynamic model when Froude numbers exceed 0.2 (0.3).
Sustainable river management often requires long-term morphological simulations. As the future is unknown, uncertainty needs to be accounted for, which may require probabilistic simulations covering a large parameter domain. Even for one-dimensional models, simulation times can be long. One of the acceleration strategies is simplification of models by neglecting terms in the governing hydrodynamic equations. Examples are the quasi-steady model and the diffusive wave model, both widely used by scientists and practitioners. We established under which conditions these simplified and often more efficient models are accurate.
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Sustainable river management often requires long-term morphological simulations. As the future is unknown, uncertainty needs to be accounted for, which may require probabilistic simulations covering a large parameter domain. Even for one-dimensional models, simulation times can be long. One of the acceleration strategies is simplification of models by neglecting terms in the governing hydrodynamic equations. Examples are the quasi-steady model and the diffusive wave model, both widely used by scientists and practitioners. We established under which conditions these simplified and often more efficient models are accurate.
Recent policy initiatives in Europe emphasize a movement towards nature-based solutions in flood management; however, a quantitative relationship between specific flood management measures and indicators of ecological health and biodiversity is difficult to establish (Penning et al., 2023). In the Netherlands, several studies have been conducted on floodplain vegetation monitoring; however, these studies are primarily focused on monitoring changes to hydraulic roughness for flood risk assessment (Harezlak et al., 2020; Penning & van de Vries, 2020). These works provide an opportunity to expand upon existing research to explicitly connect river management practices with indicators of floodplain biodiversity change in the Netherlands.
In this study, we utilize publicly available geospatial data to identify changes in land use, vegetation classification and spectral indicators of vegetation health at restoration sites associated with the Room for the River (RftR) program in the Netherlands. Completed in 2018, RftR involved over 30 river management projects constructed to reduce flood risk by lowering peak water levels (Mosselman, 2022).
Our objective is to quantify the impact of ecologically focused RftR projects on habitat heterogeneity and river connectivity in the surrounding floodplains.
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Recent policy initiatives in Europe emphasize a movement towards nature-based solutions in flood management; however, a quantitative relationship between specific flood management measures and indicators of ecological health and biodiversity is difficult to establish (Penning et al., 2023). In the Netherlands, several studies have been conducted on floodplain vegetation monitoring; however, these studies are primarily focused on monitoring changes to hydraulic roughness for flood risk assessment (Harezlak et al., 2020; Penning & van de Vries, 2020). These works provide an opportunity to expand upon existing research to explicitly connect river management practices with indicators of floodplain biodiversity change in the Netherlands.
In this study, we utilize publicly available geospatial data to identify changes in land use, vegetation classification and spectral indicators of vegetation health at restoration sites associated with the Room for the River (RftR) program in the Netherlands. Completed in 2018, RftR involved over 30 river management projects constructed to reduce flood risk by lowering peak water levels (Mosselman, 2022).
Our objective is to quantify the impact of ecologically focused RftR projects on habitat heterogeneity and river connectivity in the surrounding floodplains.
The Water Framework Directive commits European Union member states to achieve good ecological and chemical status of all water bodies. As hydromorphology is a key factor for ecological status, a consortium of 26 partners from 15 countries studied the role of hydromorphological pressures and measures in the REFORM project. Its main objective was to answer the question: How to make river restoration successful? The project developed guidance for this by structuring the information along the different stages of restoration projects and river basin management plans, posing a logical sequence of questions: How does my river work? What’s wrong? How to improve? Things can be wrong for ecological status as a result of morphological alterations. These alterations form pressures that can be countered or mitigated by measures that improve sedimentological and morphological features. We present two specific results of REFORM that focus on river morphology. First, we provide an overview of methods to assess morphological quality and diagnose alteration. Second, we present systematic cause–effect relationships for restoration measures.
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The Water Framework Directive commits European Union member states to achieve good ecological and chemical status of all water bodies. As hydromorphology is a key factor for ecological status, a consortium of 26 partners from 15 countries studied the role of hydromorphological pressures and measures in the REFORM project. Its main objective was to answer the question: How to make river restoration successful? The project developed guidance for this by structuring the information along the different stages of restoration projects and river basin management plans, posing a logical sequence of questions: How does my river work? What’s wrong? How to improve? Things can be wrong for ecological status as a result of morphological alterations. These alterations form pressures that can be countered or mitigated by measures that improve sedimentological and morphological features. We present two specific results of REFORM that focus on river morphology. First, we provide an overview of methods to assess morphological quality and diagnose alteration. Second, we present systematic cause–effect relationships for restoration measures.
Journal article
(2024)
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Michael Tritthart, Davide Vanzo, Victor Chavarrías, Annunziato Siviglia, Kees Sloff, Erik Mosselman
The sediment transport direction is affected by the bed slope. This effect is of crucial importance for two- and three-dimensional modelling of the interaction between the flow of water and the alluvial bed. It is not uncommon to find applications of numerical morphodynamic models in the literature that exaggerate the effects of transverse bed slopes on sediment transport compared to results from laboratory experiments. We investigate mathematically the consequences of such an approach, and we analyse through numerical simulations different explanations for the need to apply deviating values. The study reveals that the reason often lies in the setup of the numerical models, such as the choice of mesh resolution or the necessity to comply with specific aspects of the numerical scheme. The missing or inadequate implementation of physical processes in the model is another cause. All of these effects can be compensated by artificial diffusion added through the bed slope effect coefficients. Since increased diffusion strongly alters the physical processes of self-formed bed morphology, we recommend that modellers address the root causes of inflated erosion and deposition. Bed slope effect coefficients should be applied within the range found in the original publications.
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The sediment transport direction is affected by the bed slope. This effect is of crucial importance for two- and three-dimensional modelling of the interaction between the flow of water and the alluvial bed. It is not uncommon to find applications of numerical morphodynamic models in the literature that exaggerate the effects of transverse bed slopes on sediment transport compared to results from laboratory experiments. We investigate mathematically the consequences of such an approach, and we analyse through numerical simulations different explanations for the need to apply deviating values. The study reveals that the reason often lies in the setup of the numerical models, such as the choice of mesh resolution or the necessity to comply with specific aspects of the numerical scheme. The missing or inadequate implementation of physical processes in the model is another cause. All of these effects can be compensated by artificial diffusion added through the bed slope effect coefficients. Since increased diffusion strongly alters the physical processes of self-formed bed morphology, we recommend that modellers address the root causes of inflated erosion and deposition. Bed slope effect coefficients should be applied within the range found in the original publications.