By definition, Building with Nature solutions utilise services provided by the natural system and... more By definition, Building with Nature solutions utilise services provided by the natural system and/or provide new opportunities to that system. As a consequence, such solutions are sensitive to the status of, and interact with the surrounding system. A thorough understanding of the ambient natural system is therefore necessary to meet the required specifications and to realise the potential interactions with that system. In order to be adopted beyond the pilot scale, the potential impact of multiple BwN solutions on the natural and societal systems of a region need to be established. This requires a ‘reality check’ of the effectiveness of multiple, regional-scale applications in terms of social and environmental costs and benefits. Reality checking will help establish the upscaling potential of a certain BwN measure when addressing a larger-scale issue. Conversely, it might reveal to what extent specific smaller-scale measures are suitable in light of larger regional-scale issues. Th...
Anna Wesselink was trained as a tropical land and water development engineer, then moved into wat... more Anna Wesselink was trained as a tropical land and water development engineer, then moved into water resources research and management. This took her to the UK, the Central African Republic, and Madagascar. In order to reflect on her professional practice, she started a Ph.D. on the decision-making process in flood management in the Dutch Meuse, with particular attention to the integration of expertise, the participation of relevant social groups, the ways integrated assessment is framed, and processes of (social) learning and negotiation. In her
Building with nature (BwN) is a pro-active approach to meet the demand for hydraulic en- gineerin... more Building with nature (BwN) is a pro-active approach to meet the demand for hydraulic en- gineering infrastructures. Instead of assessing and mitigating a posteriori the environmental impacts of a set design, it considers nature as an integral part of the design right from the start of the project develop- ment process. It utilizes natural processes and provides opportunities for nature as part of the infrastruc- ture development and operation. After a first phase of 'showing that it works' in a number of pilot pro- jects, time has come to introduce the BwN-ideas into the mainstream of hydraulic engineering ('make it happen'). A number of example projects are described and lessons learned are given. The general conclu- sion is that BwN is increasingly being applied in practice, but that there are many non-technical hurdles and pitfalls.
Hydraulic engineering infrastructure is supposed to keep functioning for many years and is likely... more Hydraulic engineering infrastructure is supposed to keep functioning for many years and is likely to interfere with both the natural and the social environment at various scales. Due to its long life-cycle, hydraulic infrastructure is bound to face changing environmental conditions as well as changes in societal views on acceptable solutions. This implies that sustainability and adaptability are/should be important attributes of the design, the development and operation of hydraulic engineering infrastructure. Sustainability and adaptability are central to the Building with Nature (BwN) approach. Although nature-based design philosophies, such as BwN, have found broad support, a key issue that inhibits a wider mainstream implementation is the lack of a method to objectify BwN concepts. With objectifying, we mean turning the implicit into an explicit engineerable ‘object’, on the one hand, and specifying clear design ‘objectives’, on the other. This paper proposes the “Frame of Refer...
Public reporting burden for the collection of information is estimated to average 1 hour per resp... more Public reporting burden for the collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to a penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number.
This article shows how Dutch technological culture has historically dealt with and developed arou... more This article shows how Dutch technological culture has historically dealt with and developed around vulnerability with respect to flooding and indicates recent developments in attitude towards the flood threat. The flooding of New Orleans in the wake of Hurricane Katrina temporarily made the Dutch public worry about the flood defense infrastructure in the Netherlands, exemplified by the Delta Works. Could this happen in the Netherlands? After the flooding disaster of 1953, a system of large dams was built to offer safety from flooding with—in theory at least—protection levels that are much higher than in New Orleans. In the public's perception the protection offered is absolute. In practice not all flood defense structures are as secure as they are supposed to be, but their upgrading takes time and money. Katrina has served as a reminder of what is at stake: Can the Dutch afford to take another 10 years to restore the protection level of their flood defenses? Calls for pride in ...
Traditionally, hydraulics and geotechnics are considered as separate disciplines that have not mu... more Traditionally, hydraulics and geotechnics are considered as separate disciplines that have not much in common. We think this is a mistake: there are many overlap areas where the two can strengthen each other. Flood risk management is one example, bank/dune erosion is another, local scour near structures a third. In all these cases, geotechnical failure mechanisms are just as important as hydrodynamic and sediment transport processes. I.
This report (in Dutch) investigates the requirements on morphological knowledge and tools for the... more This report (in Dutch) investigates the requirements on morphological knowledge and tools for the design and evaluation of Room-for-the-River projects in the floodplains along the Dutch Rhine branches. The results are translated into a first set-up for a method of morphological impact assessment and a programme of further research
Journal of Geophysical Research: Earth Surface, 2013
Reduced-order models remain essential tools for meander modeling, especially for processes at lar... more Reduced-order models remain essential tools for meander modeling, especially for processes at large length scales and long time scales, probabilistic simulations, rapid assessments, or when input data are scarce or uncertain. Present reduced-order meander models consider their dependent variables either as small-amplitude variations compared to a basic state (linearity) or as varying gradually in a spatial sense (gradual variation). In a prequel, Blanckaert and de Vriend ( ) derived a nonlinear reduced-order hydrodynamic model without curvature restrictions and showed that linearity or gradual curvature variations assumptions do not hold in strongly curved channels. Moreover, in strongly curved channels, a nonlinear feedback mechanism causes the secondary flow strength to be smaller than its linear mild-curvature equivalent. In the limit of mildamplitude variations and mild curvature, their nonlinear meander flow model simplifies to a well-known linear formulation. The present paper extends this nonlinear modeling to the bed morphology in strongly curved bends, making use of Exner's sediment conservation principle. Furthermore, the model quantifying the relative influence of the downslope gravitational force is refined by considering nonlinear effects. The coupled nonlinear flow and bed morphology model yields satisfactory results for the bed topography, whereas the corresponding linear model strongly overpredicts the magnitude of the transverse bed slope. Analysis of the forcing mechanisms indicate that this erroneous behavior is caused by an overestimation of the upslope drag force due to the secondary flow.
Working in coastal planning is nearly always innovative, since no two coasts are the same. Even i... more Working in coastal planning is nearly always innovative, since no two coasts are the same. Even if they appear to be physically similar, local conditions and governance settings are usually different, thus requiring a different approach. Each project is unique, which makes coastal projects exciting and diverse. This diversity opens perspectives to a variety of ways to develop a coast, supported by a wide range of guidelines, books and articles on coastal zone management and coastal planning. In general, important factors influencing any given project are: functionality (flood protection, recreation & nature, possibly sand or gravel mining), physical characteristics (metocean, materials, bathymetry, etc), ecosystem characteristics (dune forms and habitat, foreshore and surf zone biota), economics (costs and benefits, exploitation, return on investment), governance issues, including permitting and politics, public opinion. In most innovative projects the consequences of the interventions are not exactly known, usually less so than in projects taking a traditional approach. This may constitute an obstacle to the implementation of such projects, where a combination of existing 'traditional' designs, measures and materials is often considered a safer choice. This paper claims that this practice should better be changed and demonstrates the feasibility of a more innovative approach. After an introduction of the philosophies and principles behind 'Building with Nature' and on the steps to be taken within 'Eco-dynamic Design and Development' process, two pilot 1 Expert, Royal Boskalis Westminster, Hydronamic, Papendrecht, (Netherlands),
A complex process-based model is used to simulate the formation of channels and shoals in a schem... more A complex process-based model is used to simulate the formation of channels and shoals in a schematised estuary. The model set-up enables a comparison with results obtained with idealised models. Initial as well as long-term simulations are made. Dominant wavelengths of channel-shoal patterns are investigated together with their dependency on width and depth of the basin and the local maximum velocity. Prevalent wavelengths range between 5 and 10 km and increase with increasing width and flow velocity. Initial model results are compared with idealised models. The dominant wavelengths are of the same order of magnitude as those found in the idealised model of Schramkowski et al. (2002) and their dependency on width and velocity agrees qualitatively. (Exponential) growth of the perturbations during long-term simulations provides information on the validity limits of the idealised models. Subsequent pattern formation and changes of dominant wavelengths are attributed to non-linear inte...
Many scientists feel that scientific outcomes are not sufficiently taken into account in policy-m... more Many scientists feel that scientific outcomes are not sufficiently taken into account in policy-making. The research reported in this paper shows what happens with scientific information during such a process. In 2001 the Dutch Ministry of Transport, Public Works and Water Management commissioned their regional office in Limburg to assess how flood management objectives could be achieved in future in the Dutch Meuse valley, assuming climate change will increase peak discharges. To ensure political support, regional discussion rounds were to help assess the measures previously identified. This paper discusses the ways in which hydrological and hydraulic expertise was input, understood and used in this assessment process. Project participants as a group had no trouble contesting assumptions and outcomes. Nevertheless, water expertise was generally accepted as providing facts, once basic choices such as starting situation had been discussed and agreed. The technical constraints determi...
The paper describes a numerical model for simulating sediment transport with eddyresolving 3-D mo... more The paper describes a numerical model for simulating sediment transport with eddyresolving 3-D models. This sediment model consists of four submodels: pickup, transport over the bed, transport in the water column and deposition, all based on a turbulent flow model using large-eddy simulation. The sediment is considered as uniform rigid spherical particles. This is usually a valid assumption for sand-bed rivers where underwater dune formation is most prominent. Under certain shear stress conditions, these particles are picked up from the bed due to an imbalance of gravity and flow forces. They either roll and slide on the bed in a sheet of sediment or separate from the bed and get suspended in the flow. Sooner or later, the suspended particles settle on the bed again. Each of these steps is modeled separately, yielding a physics-based process model for sediment transport, suitable for the simulation of bed morphodynamics. The sediment model is validated with theoretical findings such as the Rouse profile as well as with empirical relations of sediment bed load and suspended load transport. The current model shows good agreement with these theoretical and empirical relations. Moreover, the saltation mechanism is simulated, and the average saltation length, height, and velocity are found to be in good agreement with experimental results.
We present a 3-D physics-based high-resolution modeling approach to the dynamics of underwater ri... more We present a 3-D physics-based high-resolution modeling approach to the dynamics of underwater ripples and dunes. The flow is modeled by large eddy simulation on a Cartesian grid with local refinements. The sediment transport is modeled by computing pickup, transport over the bed, transport in the water column, and deposition of rigid spherical particles in a Lagrangian framework. The morphological development of the bed is modeled by a sediment balance equation in which the pickup and deposition from the sediment motion submodels appear as source and sink terms. The model realistically replicated the formation and migration of dunes. Model results showed a good agreement with data from five flume experiments. We subsequently applied the model to investigate the effect of sediment grain size on ripples. Finer sediments were found to yield more superimposed ripples than coarser sediments. Moreover, under the same hydrodynamic conditions, the finer sediments yielded two-dimensional bed forms, whereas for coarser sediment irregularities increased. We extended the tests to pronounced 3-D morphologies by simulating the development of local scour at a pier. The results agreed well with experimental data. The model contributes to unraveling the complex problem of small-scale morphodynamics and may be used in a wide range of applications, for instance, to develop more reliable parameterizations of small-scale processes for application in large-scale morphodynamic models.
Proceedings of the Institution of Civil Engineers - Civil Engineering, 2014
The Netherlands has adopted a new, proactive approach to developing its extensive coastal and riv... more The Netherlands has adopted a new, proactive approach to developing its extensive coastal and river works called ‘building with nature’. Rather than simply minimising or mitigating the environmental impact of harbours, navigation channels, land reclamation and flood defences, the idea is to make use of the dynamics of the natural environment and provide opportunities for natural processes. Existing concepts and ideas have been further developed and tested in a number of full-scale pilot experiments, including sand engines, oyster reefs and waveattenuating forests. This paper describes a number of these experiments along with the preliminary results and lessons learned.
In spite of its importance, little is known about the turbulence characteristics in open-channel ... more In spite of its importance, little is known about the turbulence characteristics in open-channel bends. This paper reports on an experimental investigation of turbulence in one cross section of an open-channel bend. Typical flow features are a bicellular pattern of cross-stream circulation (secondary flow) and a turbulence activity in the outer bend that is significantly less than in the equivalent straight uniform shear flow. Measured distributions are given of the turbulent kinetic energy, its production, the mixing coefficients, some parameters characterizing the turbulence structure, and the fourth-order correlations of the turbulent velocity fluctuations. The transport equation for the turbulent kinetic energy is evaluated term by term, on the basis of the measured data. The results show that the turbulence structure is different from straight uniform flow, in that the Reynolds stress tensor is more diagonally dominant. This is shown to be the main cause of the observed reducti...
The question whether it is time for marine morphodynamic models to take into account the 3-D natu... more The question whether it is time for marine morphodynamic models to take into account the 3-D nature of water and sediment motion is discussed starting from practical demand and the state-of-the-art in basic knowledge and model development. This leads to the observation that there is a clear practical demand, and that suitable software environments and some 3-D model components exist, but that the basic knowledge on 3-D morphodynamic processes and the necessary know-how for utilizing these models are still insufficient. Hence it is concluded that there is an urgent need for modelling-oriented research on 3-D marine morphodynamics, but that it is too early to develop modelling facilities for practical application. Die vorliegende Arbeit befal3t sich mit der Frage, ob marine morphodynamische Modelle auch die Drei-dimensionalit&t von Wasser-und Sedimentbewegungen berQcksichtigen sollten und geht dabei auf die bestehende Nachfrage sowie auf den heutigen Entwicklungsstand der Modelle ein. Sie gelangt zu dem Schlui3, dal3 zwar eindeutig Nachfrage nach solchen Modellen besteht und bereits geeignete Software-und 3D-Modellkomponenten vorhanden sind, aber die Kenntnisse 0ber 3D-morphodynamische Prozesse und die Anwendung solcher Modelle bisher unzureichend sind. Es wird daraus gefolgert, dal3 ein dringender modellorientierter Forschungsbedarf zu marinen morphodynamischen 3-D-Modellen besteht, es aber for die Entwicklung von Modellen fQr die Praxis noch zu fff)h ist.
Climate change and a river’s response to it are likely to be slow processes as compared to the re... more Climate change and a river’s response to it are likely to be slow processes as compared to the responses to direct human interventions such as engineering works. Therefore, we have to look at timescales of centuries. Such timescales are difficult to be covered by numerical models and, moreover, uncertainties are so large that the degree of detail offered by numerical model simulations hardly pays off in terms of extra information. Therefore, we fall back on simple basic models providing first-order insight into a river’s long-term behaviour. Starting from the basic drivers and controls of large-scale river morphology, we describe longterm changes as can be expected from climate change and long-lasting human interventions.
By definition, Building with Nature solutions utilise services provided by the natural system and... more By definition, Building with Nature solutions utilise services provided by the natural system and/or provide new opportunities to that system. As a consequence, such solutions are sensitive to the status of, and interact with the surrounding system. A thorough understanding of the ambient natural system is therefore necessary to meet the required specifications and to realise the potential interactions with that system. In order to be adopted beyond the pilot scale, the potential impact of multiple BwN solutions on the natural and societal systems of a region need to be established. This requires a ‘reality check’ of the effectiveness of multiple, regional-scale applications in terms of social and environmental costs and benefits. Reality checking will help establish the upscaling potential of a certain BwN measure when addressing a larger-scale issue. Conversely, it might reveal to what extent specific smaller-scale measures are suitable in light of larger regional-scale issues. Th...
Anna Wesselink was trained as a tropical land and water development engineer, then moved into wat... more Anna Wesselink was trained as a tropical land and water development engineer, then moved into water resources research and management. This took her to the UK, the Central African Republic, and Madagascar. In order to reflect on her professional practice, she started a Ph.D. on the decision-making process in flood management in the Dutch Meuse, with particular attention to the integration of expertise, the participation of relevant social groups, the ways integrated assessment is framed, and processes of (social) learning and negotiation. In her
Building with nature (BwN) is a pro-active approach to meet the demand for hydraulic en- gineerin... more Building with nature (BwN) is a pro-active approach to meet the demand for hydraulic en- gineering infrastructures. Instead of assessing and mitigating a posteriori the environmental impacts of a set design, it considers nature as an integral part of the design right from the start of the project develop- ment process. It utilizes natural processes and provides opportunities for nature as part of the infrastruc- ture development and operation. After a first phase of 'showing that it works' in a number of pilot pro- jects, time has come to introduce the BwN-ideas into the mainstream of hydraulic engineering ('make it happen'). A number of example projects are described and lessons learned are given. The general conclu- sion is that BwN is increasingly being applied in practice, but that there are many non-technical hurdles and pitfalls.
Hydraulic engineering infrastructure is supposed to keep functioning for many years and is likely... more Hydraulic engineering infrastructure is supposed to keep functioning for many years and is likely to interfere with both the natural and the social environment at various scales. Due to its long life-cycle, hydraulic infrastructure is bound to face changing environmental conditions as well as changes in societal views on acceptable solutions. This implies that sustainability and adaptability are/should be important attributes of the design, the development and operation of hydraulic engineering infrastructure. Sustainability and adaptability are central to the Building with Nature (BwN) approach. Although nature-based design philosophies, such as BwN, have found broad support, a key issue that inhibits a wider mainstream implementation is the lack of a method to objectify BwN concepts. With objectifying, we mean turning the implicit into an explicit engineerable ‘object’, on the one hand, and specifying clear design ‘objectives’, on the other. This paper proposes the “Frame of Refer...
Public reporting burden for the collection of information is estimated to average 1 hour per resp... more Public reporting burden for the collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to a penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number.
This article shows how Dutch technological culture has historically dealt with and developed arou... more This article shows how Dutch technological culture has historically dealt with and developed around vulnerability with respect to flooding and indicates recent developments in attitude towards the flood threat. The flooding of New Orleans in the wake of Hurricane Katrina temporarily made the Dutch public worry about the flood defense infrastructure in the Netherlands, exemplified by the Delta Works. Could this happen in the Netherlands? After the flooding disaster of 1953, a system of large dams was built to offer safety from flooding with—in theory at least—protection levels that are much higher than in New Orleans. In the public's perception the protection offered is absolute. In practice not all flood defense structures are as secure as they are supposed to be, but their upgrading takes time and money. Katrina has served as a reminder of what is at stake: Can the Dutch afford to take another 10 years to restore the protection level of their flood defenses? Calls for pride in ...
Traditionally, hydraulics and geotechnics are considered as separate disciplines that have not mu... more Traditionally, hydraulics and geotechnics are considered as separate disciplines that have not much in common. We think this is a mistake: there are many overlap areas where the two can strengthen each other. Flood risk management is one example, bank/dune erosion is another, local scour near structures a third. In all these cases, geotechnical failure mechanisms are just as important as hydrodynamic and sediment transport processes. I.
This report (in Dutch) investigates the requirements on morphological knowledge and tools for the... more This report (in Dutch) investigates the requirements on morphological knowledge and tools for the design and evaluation of Room-for-the-River projects in the floodplains along the Dutch Rhine branches. The results are translated into a first set-up for a method of morphological impact assessment and a programme of further research
Journal of Geophysical Research: Earth Surface, 2013
Reduced-order models remain essential tools for meander modeling, especially for processes at lar... more Reduced-order models remain essential tools for meander modeling, especially for processes at large length scales and long time scales, probabilistic simulations, rapid assessments, or when input data are scarce or uncertain. Present reduced-order meander models consider their dependent variables either as small-amplitude variations compared to a basic state (linearity) or as varying gradually in a spatial sense (gradual variation). In a prequel, Blanckaert and de Vriend ( ) derived a nonlinear reduced-order hydrodynamic model without curvature restrictions and showed that linearity or gradual curvature variations assumptions do not hold in strongly curved channels. Moreover, in strongly curved channels, a nonlinear feedback mechanism causes the secondary flow strength to be smaller than its linear mild-curvature equivalent. In the limit of mildamplitude variations and mild curvature, their nonlinear meander flow model simplifies to a well-known linear formulation. The present paper extends this nonlinear modeling to the bed morphology in strongly curved bends, making use of Exner's sediment conservation principle. Furthermore, the model quantifying the relative influence of the downslope gravitational force is refined by considering nonlinear effects. The coupled nonlinear flow and bed morphology model yields satisfactory results for the bed topography, whereas the corresponding linear model strongly overpredicts the magnitude of the transverse bed slope. Analysis of the forcing mechanisms indicate that this erroneous behavior is caused by an overestimation of the upslope drag force due to the secondary flow.
Working in coastal planning is nearly always innovative, since no two coasts are the same. Even i... more Working in coastal planning is nearly always innovative, since no two coasts are the same. Even if they appear to be physically similar, local conditions and governance settings are usually different, thus requiring a different approach. Each project is unique, which makes coastal projects exciting and diverse. This diversity opens perspectives to a variety of ways to develop a coast, supported by a wide range of guidelines, books and articles on coastal zone management and coastal planning. In general, important factors influencing any given project are: functionality (flood protection, recreation & nature, possibly sand or gravel mining), physical characteristics (metocean, materials, bathymetry, etc), ecosystem characteristics (dune forms and habitat, foreshore and surf zone biota), economics (costs and benefits, exploitation, return on investment), governance issues, including permitting and politics, public opinion. In most innovative projects the consequences of the interventions are not exactly known, usually less so than in projects taking a traditional approach. This may constitute an obstacle to the implementation of such projects, where a combination of existing 'traditional' designs, measures and materials is often considered a safer choice. This paper claims that this practice should better be changed and demonstrates the feasibility of a more innovative approach. After an introduction of the philosophies and principles behind 'Building with Nature' and on the steps to be taken within 'Eco-dynamic Design and Development' process, two pilot 1 Expert, Royal Boskalis Westminster, Hydronamic, Papendrecht, (Netherlands),
A complex process-based model is used to simulate the formation of channels and shoals in a schem... more A complex process-based model is used to simulate the formation of channels and shoals in a schematised estuary. The model set-up enables a comparison with results obtained with idealised models. Initial as well as long-term simulations are made. Dominant wavelengths of channel-shoal patterns are investigated together with their dependency on width and depth of the basin and the local maximum velocity. Prevalent wavelengths range between 5 and 10 km and increase with increasing width and flow velocity. Initial model results are compared with idealised models. The dominant wavelengths are of the same order of magnitude as those found in the idealised model of Schramkowski et al. (2002) and their dependency on width and velocity agrees qualitatively. (Exponential) growth of the perturbations during long-term simulations provides information on the validity limits of the idealised models. Subsequent pattern formation and changes of dominant wavelengths are attributed to non-linear inte...
Many scientists feel that scientific outcomes are not sufficiently taken into account in policy-m... more Many scientists feel that scientific outcomes are not sufficiently taken into account in policy-making. The research reported in this paper shows what happens with scientific information during such a process. In 2001 the Dutch Ministry of Transport, Public Works and Water Management commissioned their regional office in Limburg to assess how flood management objectives could be achieved in future in the Dutch Meuse valley, assuming climate change will increase peak discharges. To ensure political support, regional discussion rounds were to help assess the measures previously identified. This paper discusses the ways in which hydrological and hydraulic expertise was input, understood and used in this assessment process. Project participants as a group had no trouble contesting assumptions and outcomes. Nevertheless, water expertise was generally accepted as providing facts, once basic choices such as starting situation had been discussed and agreed. The technical constraints determi...
The paper describes a numerical model for simulating sediment transport with eddyresolving 3-D mo... more The paper describes a numerical model for simulating sediment transport with eddyresolving 3-D models. This sediment model consists of four submodels: pickup, transport over the bed, transport in the water column and deposition, all based on a turbulent flow model using large-eddy simulation. The sediment is considered as uniform rigid spherical particles. This is usually a valid assumption for sand-bed rivers where underwater dune formation is most prominent. Under certain shear stress conditions, these particles are picked up from the bed due to an imbalance of gravity and flow forces. They either roll and slide on the bed in a sheet of sediment or separate from the bed and get suspended in the flow. Sooner or later, the suspended particles settle on the bed again. Each of these steps is modeled separately, yielding a physics-based process model for sediment transport, suitable for the simulation of bed morphodynamics. The sediment model is validated with theoretical findings such as the Rouse profile as well as with empirical relations of sediment bed load and suspended load transport. The current model shows good agreement with these theoretical and empirical relations. Moreover, the saltation mechanism is simulated, and the average saltation length, height, and velocity are found to be in good agreement with experimental results.
We present a 3-D physics-based high-resolution modeling approach to the dynamics of underwater ri... more We present a 3-D physics-based high-resolution modeling approach to the dynamics of underwater ripples and dunes. The flow is modeled by large eddy simulation on a Cartesian grid with local refinements. The sediment transport is modeled by computing pickup, transport over the bed, transport in the water column, and deposition of rigid spherical particles in a Lagrangian framework. The morphological development of the bed is modeled by a sediment balance equation in which the pickup and deposition from the sediment motion submodels appear as source and sink terms. The model realistically replicated the formation and migration of dunes. Model results showed a good agreement with data from five flume experiments. We subsequently applied the model to investigate the effect of sediment grain size on ripples. Finer sediments were found to yield more superimposed ripples than coarser sediments. Moreover, under the same hydrodynamic conditions, the finer sediments yielded two-dimensional bed forms, whereas for coarser sediment irregularities increased. We extended the tests to pronounced 3-D morphologies by simulating the development of local scour at a pier. The results agreed well with experimental data. The model contributes to unraveling the complex problem of small-scale morphodynamics and may be used in a wide range of applications, for instance, to develop more reliable parameterizations of small-scale processes for application in large-scale morphodynamic models.
Proceedings of the Institution of Civil Engineers - Civil Engineering, 2014
The Netherlands has adopted a new, proactive approach to developing its extensive coastal and riv... more The Netherlands has adopted a new, proactive approach to developing its extensive coastal and river works called ‘building with nature’. Rather than simply minimising or mitigating the environmental impact of harbours, navigation channels, land reclamation and flood defences, the idea is to make use of the dynamics of the natural environment and provide opportunities for natural processes. Existing concepts and ideas have been further developed and tested in a number of full-scale pilot experiments, including sand engines, oyster reefs and waveattenuating forests. This paper describes a number of these experiments along with the preliminary results and lessons learned.
In spite of its importance, little is known about the turbulence characteristics in open-channel ... more In spite of its importance, little is known about the turbulence characteristics in open-channel bends. This paper reports on an experimental investigation of turbulence in one cross section of an open-channel bend. Typical flow features are a bicellular pattern of cross-stream circulation (secondary flow) and a turbulence activity in the outer bend that is significantly less than in the equivalent straight uniform shear flow. Measured distributions are given of the turbulent kinetic energy, its production, the mixing coefficients, some parameters characterizing the turbulence structure, and the fourth-order correlations of the turbulent velocity fluctuations. The transport equation for the turbulent kinetic energy is evaluated term by term, on the basis of the measured data. The results show that the turbulence structure is different from straight uniform flow, in that the Reynolds stress tensor is more diagonally dominant. This is shown to be the main cause of the observed reducti...
The question whether it is time for marine morphodynamic models to take into account the 3-D natu... more The question whether it is time for marine morphodynamic models to take into account the 3-D nature of water and sediment motion is discussed starting from practical demand and the state-of-the-art in basic knowledge and model development. This leads to the observation that there is a clear practical demand, and that suitable software environments and some 3-D model components exist, but that the basic knowledge on 3-D morphodynamic processes and the necessary know-how for utilizing these models are still insufficient. Hence it is concluded that there is an urgent need for modelling-oriented research on 3-D marine morphodynamics, but that it is too early to develop modelling facilities for practical application. Die vorliegende Arbeit befal3t sich mit der Frage, ob marine morphodynamische Modelle auch die Drei-dimensionalit&t von Wasser-und Sedimentbewegungen berQcksichtigen sollten und geht dabei auf die bestehende Nachfrage sowie auf den heutigen Entwicklungsstand der Modelle ein. Sie gelangt zu dem Schlui3, dal3 zwar eindeutig Nachfrage nach solchen Modellen besteht und bereits geeignete Software-und 3D-Modellkomponenten vorhanden sind, aber die Kenntnisse 0ber 3D-morphodynamische Prozesse und die Anwendung solcher Modelle bisher unzureichend sind. Es wird daraus gefolgert, dal3 ein dringender modellorientierter Forschungsbedarf zu marinen morphodynamischen 3-D-Modellen besteht, es aber for die Entwicklung von Modellen fQr die Praxis noch zu fff)h ist.
Climate change and a river’s response to it are likely to be slow processes as compared to the re... more Climate change and a river’s response to it are likely to be slow processes as compared to the responses to direct human interventions such as engineering works. Therefore, we have to look at timescales of centuries. Such timescales are difficult to be covered by numerical models and, moreover, uncertainties are so large that the degree of detail offered by numerical model simulations hardly pays off in terms of extra information. Therefore, we fall back on simple basic models providing first-order insight into a river’s long-term behaviour. Starting from the basic drivers and controls of large-scale river morphology, we describe longterm changes as can be expected from climate change and long-lasting human interventions.
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Papers by Huib de Vriend