Schuurman F.,University Utrecht |
Schuurman F.,Royal Haskoning |
Marra W.A.,University Utrecht |
Kleinhans M.G.,University Utrecht
Journal of Geophysical Research: Earth Surface | Year: 2013
Braided rivers have complicated and dynamic bar patterns, which are challenging to fully understand and to predict both qualitatively and quantitatively. Linear theory ignores nonlinear processes that dominate fully developed bars, whereas natural river patterns are determined by the combined effects of boundary conditions, initial conditions such as planimetric forcing by fixed banks and the physical processes. Here we determine the capability of a state-of-the-art physics-based morphological model to reproduce morphology and dynamics characteristic of braided rivers and determine the model sensitivity to generally used constitutive relations for flow and sediment transport. We use the 2-D depth-averaged morphodynamic model Delft3D, which includes the necessary spiral flow and bed slope effects on morphology. We present idealized scenarios with the smallest possible number of enforced details in the planform and boundary conditions in order to allow free development of bars driven by the physical processes in the model. We analyze bar and channel shapes and dynamics quantified by a number of complementary metrics and compare these with imagery, field data captured in empirical relations, flume experiments, and predictions by linear analyses. The results show that the chosen set of boundary conditions and physics in the numerical model is sufficient to produce many morphological characteristics and dynamics of a braided river but insufficient for long-term modeling. Initially, braiding intensity with low-amplitude bars is high in agreement with linear analysis. In a second stage when bars merge, split, and increase amplitude up to the water surface, the shape, size, and dynamics of individual bars compare well to those in natural rivers. However, long-term modeling results in a reduction of bar and channel dynamics and formation of exaggerated bar height and length. This suggests that additional processes, such as physics-based bank erosion, or enforced fluctuations in boundary conditions, such as spatial-temporal discharge variation, are necessary for the simulation of a dynamic equilibrium river. The most important outcome is that the modeled pattern of bars and channels is highly sensitive to the constitutive relation for bed slope effects that is used in many morphological models. Regardless of this sensitivity and present model limitations of many models, this study shows that physics-based modeling of sand-bed braided improves our understanding and prediction of morphological patterns and dynamics in sand-bed braided rivers. Key Points Physics-based model produced braided topography + realistic short-term dynamics Large uncertainty in physics-based modeling due to constitutive relations Modeled processes and constant Q insufficient for realistic long-term braiding ©2013. American Geophysical Union. All Rights Reserved.
Walkden M.J.,Royal Haskoning |
Hall J.W.,Newcastle University
Journal of Coastal Research | Year: 2011
This paper describes the development, behaviour, and application of a mesoscale numerical geomorphological model of eroding soft rock and beach shores. The model, SCAPE (Soft-Cliff and Platform Erosion), describes coastal processes and engineering interventions and is a suitable tool for testing management strategies. The mesoscale capability of SCAPE arises because it includes a broad system: its principal modules describe wave transformation, platform erosion, and a (one-line) beach. Feedback within and between the modules regulates their behaviour, brings long-term (dynamic) stability, and allows quantified representation of qualitatively different shore behaviours. SCAPE is demonstrated through the construction of a model of more than 30 km of the North Norfolk coast. A precalibration initialisation phase is required to allow dynamic equilibrium to emerge. Once initialised, calibrated, and validated against an 87-year record, the model is used to explore the development of the North Norfolk coast from 2003 to 2053 under six management scenarios. The model is also used to demonstrate the losses and benefits of erosion under these scenarios and to reveal two qualitatively different modes of behaviour, termed rock strength limited erosion and sediment transport limited erosion. Some generic implications of these different modes are discussed. © 2011, the Coastal Education & Research Foundation (CERF).
van Vossen W.J.,Royal Haskoning
Osterreichische Wasser- und Abfallwirtschaft | Year: 2010
The current Dutch policy concerning landfills is based on isolation of the waste from its environment. Infiltration of rain water is limited by means of an impermeable top liner to such an extent that emissions to groundwater are reduced to acceptable levels. This approach however is not a sustainable solution. The pollution potential stays in place and will be imminent, whenever the isolation measures fail. Therefore the isolation requires eternal aftercare. A group of Dutch landfill owners consider isolation and eternal aftercare not a real and sustainable solution for the mitigation of unacceptable emissions due to landfills. So they initiated a project 'Sustainable emission reduction at present landfills' to evaluate the possibilities and effects of sustainable landfill-methodologies at present landfills. Three landfills have been selected (Vlagheide, Kragge and Wieringermeer) for full scale demonstration projects. The present paper reports on the approach and methodologies to be applied. © 2010 Springer-Verlag.
Ashton A.D.,Woods Hole Oceanographic Institution |
Walkden M.J.A.,Royal Haskoning |
Dickson M.E.,University of Auckland
Marine Geology | Year: 2011
Basic formulae have long been used to predict the effects of sea-level rise on coastal recession; for instance, the geometric 'Bruun rule' (and its modifications) has often been applied to sandy coasts, both low-lying and steep. However, the behavior of rocky coasts, whether strongly or poorly lithified, should be significantly different than that of sandy coasts given that rocky coast evolution depends upon the irreversible breakdown of rock, whereas sandy and depositional systems are controlled by the transport (and related transport gradients) of mobile sediment. Here, we investigate the basis of a modeled relationship which suggests (with a number of caveats) that the equilibrium soft-rock cliff recession rate can be estimated by the square root of the relative change in sea-level rise rate. Although this relationship was derived using the numerical model SCAPE (Soft Cliff And Platform Erosion), which simulates a broad soft-rock cliffed coastal system driven by stochastic environmental forces, here we show that a simplified modeling approach also reproduces the relationship. We then extend this approach to develop a general theoretical framework within which it is possible to consider the potential responses of the different types of cliffed coasts to changes in the rate of sea level rise. Although a wide variety of processes affect different coastal settings, this framework demonstrates how the strength and the nature of feedbacks within cliffed system control their response to sea-level rise. This suggests that cliffed environments controlled by different processes can still respond in similar ways to changes in the rate of sea-level rise. Most rocky coasts would be expected to respond as a damped, or 'negative feedback' system between the extremes of a 'no feedback' system that is unresponsive to sea-level rise rate and an 'instant response' system characterized by a linear response similar to the Bruun rule. This framework suggests that a potential 'inverse feedback' case could also exist, in which increased rates of sea-level rise reduce the rate of coastal recession. In almost all cases, it is apparent that cliffed coast response to sea-level rise depends not only upon the total elevation change of sea level, but on the rate of the sea-level rise. These theoretical investigations and the classifications presented provide a framework to understand the behavior of systems affected by a wide array of processes, and provide expectations that can be tested using more complex models of cliffed coast evolution in a variety of environments, whether sandy or rocky, hard or soft. © 2011.
de Vos P.H.,Royal Haskoning
Notes on Numerical Fluid Mechanics and Multidisciplinary Design | Year: 2015
In 2012 The Netherlands Parliament agreed to a revision of the national Noise Legislation, including the introduction of Noise Production Ceilings for national motorways and railways . Ceiling values are derived from the current calculated noise levels at a large number of reference points along the road or track. Ceiling values are open to the general public. The infrastructure manager is responsible that the ceiling values are respected at all times, i.e. including due to traffic growth. Within the ceiling values he then has an autonomous right to implement mitigation measures or even to apply changes to the track, without further legal procedure. To residents the new system offers more certainty with respect to their future noise situation. To the infrastructure manager it offers flexibility to tune the railway�s capacity to the transport demand without lengthy legal procedures. The system suffers from low credibility both with the general public and with politicians. To a certain extent this is due to the complexity of the first implementation of the system. The low credibility leads to a strong wish to check calculated levels by means of measurements. The next few years, after the first implementation problems have been solved, will decide if and how measurements can solve the credibility problem. � Springer-Verlag Berlin Heidelberg 2015.