Dutch River Waal Research Articles

Revisiting Waal River Training by Historical Reconstruction

The Dutch River Waal, a branch of the Rhine, has been trained for centuries to mitigate the effects of ice-jams and improve navigation. The works, started in 1850, involved river straightening and narrowing by a series of transverse groynes. Besides fulfilling their goal, the groynes also created the need to raise flood protection works and caused undesirable channel incision. This study assesses the effectiveness of training the river with a longitudinal wall instead of with groynes. The investigation analyzes the long-term response of the historical river with a two-dimensional depth-averaged (2DH) morphodynamic model. The results show that the wall would create two parallel channels, one becoming deeper and the other one shallower. The former would be as suitable for navigation as an equally-wide channel obtained with groynes. The latter would contribute in conveying water during high flow events and improve the river ecology. Training the river with a wall would also lessen channel incision. The best performance is obtained if the wall is built on the channel centerline, starting just upstream of a point bar top.

Assessing stakeholder perceptions of landscape and place in the context of a major river intervention: a call for their inclusion in adaptive management

AbstractAdaptive management strategies are required to manage multi-actor and multifunctional river landscapes. Such strategies need to be inclusive of perspectives of different stakeholders. We present a case study of a pilot engineering project in the Dutch river Waal, which drastically changed the appearance of the river landscape. We study perceptions of four stakeholder groups (residents, recreational anglers, recreational boaters and shipping professionals) regarding the impacts of this intervention on landscape values, including aesthetics, naturalness, biodiversity, flood safety and accessibility. Results show that stakeholders differ in which functions of the river landscape they find important and how they perceive the longitudinal dams to influence the landscape. They also differ in levels of place attachment and trust in the responsible authority. Shipping professionals stand out for their more negative evaluations of the dams compared to the other stakeholders, while especially residents demonstrate high levels of place identity and connection with nature. Residents also feel that the dams are improving flood risk safety in the area, and they positively evaluate knowledge and skills of Dutch water managers. These results provide water managers with much needed insights into landscape functions valued by different stakeholder groups and those perceived as most endangered by landscape interventions.

Uncertainty quantification of flood mitigation predictions and implications for interventions

Abstract. Reduction of water levels during river floods is key in preventing damage and loss of life. Computer models are used to design ways to achieve this and assist in the decision-making process. However, the predictions of computer models are inherently uncertain, and it is currently unknown to what extent that uncertainty affects predictions of the effect of flood mitigation strategies. In this study, we quantify the uncertainty of flood mitigation interventions on the Dutch River Waal, based on 39 different sources of uncertainty and 12 intervention designs. The aim of each intervention is to reduce flood water levels. Our objective is to investigate the uncertainty of model predictions of intervention effect and to explore relationships that may aid in decision-making. We identified the relative uncertainty, defined as the ratio between the confidence interval and the expected effect, as a useful metric to compare uncertainty between different interventions. Using this metric, we show that intervention effect uncertainty behaves like a traditional backwater curve with an approximately constant relative uncertainty value. In general, we observe that uncertainty scales with effect: high flood level decreases have high uncertainty, and, conversely, small effects are accompanied by small uncertainties. However, different interventions with the same expected effect do not necessarily have the same uncertainty. For example, our results show that the large-scale but relatively ineffective intervention of floodplain smoothing by removing vegetation has much higher uncertainty compared to alternative options. Finally, we show how a level of acceptable uncertainty can be defined and how this can affect the design of interventions. In general, we conclude that the uncertainty of model predictions is not large enough to invalidate model-based intervention design, nor small enough to neglect altogether. Instead, uncertainty information is valuable in the selection of alternative interventions.

Exploring place attachment and visions of nature of water-based recreationists: the case of the longitudinal dams

This study concerns an innovative project in the Dutch river Waal: the construction of longitudinal dams. By splitting the river into a main and secondary channel, these dams significantly impact the river landscape and the way it is used by different stakeholders. We report the results of a baseline study of the expectations local water-based recreationists (fishermen and boaters) had of the longitudinal dams before they were constructed. In addition, we explore their levels of place attachment, and use the visions of nature approach to elicit their lay philosophy of nature. We found that fishermen were more strongly attached to the area than boaters. Though expectations of the dams were generally negative, this differed significantly between fishermen and boaters, and between different dimensions of landscape change. We demonstrate the relevance of place attachment and visions of nature for understanding how recreationists perceive landscape change.

Flow Bifurcation at a Longitudinal Training Dam: Effects on Local Morphology

Longitudinal training dams (LTDs) have been built over a length of 10 km in the Dutch River Waal as an alternative to groyne fields, splitting the river in a fairway and a bank-connected side channel in the inner bend. Here, we study the physical mechanisms governing the three-dimensional flow and its effect on local morphology at the flow divide using a mobile bed physical model of an LTD, centred around a side channel intake. In line with previous experiments, polystyrene granules are used as a lightweight sediment that allows to achieve dynamic similarity between the model and the prototype. An Acoustic Doppler Velocimetry (ADV) profiler is used to monitor the flow characteristics, whereas a line laser scanner set-up is used to measure the morphological imprint of the flow near the bifurcation point. To study the dependence of the results on the sill height at the side channel intake, different forms and heights of the sill are used. First results show striking similarities with measurements from the field pilot in the Waal River, as well as larger sedimentation in the side channel for a uniform low sill compared to a downstream increasing sill height.

Implementing participatory monitoring in river management: The role of stakeholders' perspectives and incentives

Involving local stakeholders in monitoring has the potential to stimulate learning and improve management responses. However, there is limited understanding about factors which influence implementation and success. This paper reviews local stakeholders' perceptions with respect to the construction of longitudinal dams in the Dutch river Waal, and explores their incentives to be involved in monitoring the effects of this intervention. Interviews with key stakeholders showed that concerns and (dis)trust are important incentives for participating in monitoring. Surveys of local residents, recreational anglers and boaters, and shipping professionals mapped their level of trust, attachment to the river landscape and evaluation of the effects of the longitudinal dams. Our case study shows that incentives for participation differ between stakeholder groups, and that research into their perceptions of the local environment can inform water managers on how to involve these groups in participatory monitoring.

Discussion of “Theoretical Analysis of Wing Dike Impact on River Flood Stages” by Fredrik Huthoff, Nicholas Pinter, and Jonathan W. F. Remo

The theoretical analysis proposed in the original paper is an oversimplified method to quantify an extremely complex and dynamic hydraulic problem. The basis of this analysis is the effective n value formula developed by Yossef (2004, 2005). Although these relationships can give insight into the relationship between the effective roughness in the dike zone and submergence, it is only suitable to deduce trends rather than quantify accurate magnitudes of change. Background into the development of Eq. (3) is necessary to understand its limitations. Eq. (3) was developed using a fixed bed physical model scaled to the dimensions and geometry of a dike field in the Dutch River Waal where the wing dike crest elevation, spacing, and length remained fixed throughout the study. There are major differences in geometry and spacing of dikes used by the Dutch and those on the Middle Mississippi River. The dikes used by the Dutch have a much higher crest elevation, closer spacing, and higher contraction ratios. Eq. (3) is dependent on the drag coefficient CD found in Eq. (4). The drag coefficient, CD, was developed using empirical data from the previously mentioned flume study and assumed to be in accordance with a power function. The coefficients a and b in Eq. (4) are only appropriate for the dimensions and channel geometry tested, and are not applicable to the much different geometry and dimensions of the Middle Mississippi River. The limitations of the relationships, which are the foundation of the original paper [Eqs. (3) and (4)], combined with concerns of the applicability of the relationship to the geometrically different Middle Mississippi River, make it difficult for the authors of the original paper to base sweeping conclusions off small changes (decimeter range) in an overly simplistic analysis. Another limitation the conclusions presented by the authors of the original paper is the model used in the original paper is extremely sensitive to the input data; small changes to in bank and/or channel roughness, wing dike crest height, and/or bed level change can have major impacts on the resulting water level difference, including resulting in negative values. An example of the sensitivity of the model to the input values is the resulting water level differences using the input values in the original paper. As detailed in the publisher’s note, the model developed by the authors of the original paper originally had an inadvertent error in the calculation of Manning’s n from Eq. (3). This resulted in effective roughness values in the bank zone with dikes (neff ) of approximately 0.6 s m−1=3, which is an order of magnitude too high. In combination with the correction of the math error, critical input values were changed in the corrected analysis. The bank roughness values (nb) used in the original version were 0.031, 0.032, 0.027, and 0.027 for St. Louis, Chester, Grand Tower, and Thebes, respectively. In the corrected analysis the original n values were decreased by over 40% to physically unrealistic values (Table 1). Had the authors of the original paper only corrected the math error and used the original values of base roughness in the bank zone with resulting calibrated bed changes of−0.80,−0.26,þ0.72, and −0.27 m at St. Louis, Chester, Grand Tower, and Thebes, respectively, the resulting water level difference would have been −0.12 m at St. Louis, þ0.21 m at Chester, þ0.84 m at Grand Tower, and −0.00 m at Thebes for 4Qave. These values of water level change lead to a conclusion on the impact of wing dikes on flood stages that is in conflict with what is presented in the original paper, but shared by many scientists (Watson et al. 2013; USGAO 2011; Huizinga 2009). A major issue with the roughness values used in the corrected paper is the resulting velocity distribution in the channel. Main channel velocities for the no dike, T0, condition at St. Louis were taken from a reconstruction of the model used in the original paper. At Qave, both main channel and bank zone velocities were equal. At 4Qave, the bank zone velocity was 135% of the channel velocity [Fig. 1(a)]. Conversely, had the authors of the original paper used similar roughness values for the channel and bank zone (as done in the

Uncertainty of design water levels due to combined bed form and vegetation roughness in the Dutch River Waal

AbstractTwo‐dimensional hydrodynamic models are frequently used for flood protection studies to compute inundation patterns and to estimate potential economic damage. However, the modelling of river processes involves numerous uncertainties. Knowledge of the type and magnitude of uncertainties is crucial for a meaningful interpretation of the model outcomes and its usefulness in decision making. The objective of this study was to quantify the uncertainty in the design water levels due to uncertain bed form and vegetation roughness for the Dutch River Waal. We quantified and combined these sources of uncertainty by means of a Monte Carlo simulation. The results showed that the 95% confidence interval of the design water levels is 0.49 m, 0.34 m and 0.12 m for bed form, vegetation classification and vegetation roughness parameterisation, respectively, and approximately 0.68 m for the combined roughness. These uncertainties are significant in view of Dutch river management practice.

Quantification of uncertainty in design water levels due to uncertain bed form roughness in the Dutch river Waal

AbstractHydrodynamic river models are applied to design and evaluate measures for purposes such as safety against flooding. The modelling of river processes involves numerous uncertainties, resulting in uncertain model results. Knowledge of the type and magnitude of these uncertainties is crucial for a meaningful interpretation of the model results. Uncertainty in the hydraulic roughness due to bed forms is one of the main contributors to the uncertainty in the modelled water levels. The aim of this study was to quantify the uncertainty in the bed form roughness under design conditions and quantify the effect on the design water levels in the Dutch river Waal. Five roughness models that predict bed form roughness based on measured bed form and flow characteristics were extrapolated to design conditions. The results show that the 95% confidence interval of the predicted Nikuradse roughness values under design conditions ranges from 0.32 to 1.03 m. This uncertainty was propagated through the two‐dimensional hydrodynamic model, WAQUA, by means of a Monte Carlo simulation for an idealized schematization of the Dutch river Waal. The uncertain bed form roughness results in an uncertainty in the design water levels, with a 95% confidence interval of 0.53 m, which is significant for Dutch river management practice. The uncertainty in the bed form roughness was mainly caused by a lack of knowledge about the physical process of bed form evolution that causes roughness. An improved estimation of bed form roughness can significantly reduce the uncertainty in the design water levels. Copyright © 2012 John Wiley & Sons, Ltd.

Flow Details near River Groynes: Experimental Investigation

Experiments have been carried out in a fixed-bed flume for a schematized straight river reach with groynes on one side to study the dynamics of the flow near groynes. The flume had a geometrical scale of 1:40, based on typical dimensions of the Dutch River Waal. Both emergent and submerged groynes were studied. The measurements demonstrate the differences in the nature of the turbulence between submerged and emerged groynes stages; and provide insight into the flow pattern in the vicinity of groynes, the shape and the extent of the mixing layer at different flow stages, and the dynamic behavior of the velocity along the mixing layer between the main channel and the groyne fields. A parameterization of the turbulence characteristics of the flow near groynes is presented. Large-scale velocity fluctuations are found in all test cases, with timescales that vary with the flow stage. The large-scale u and v velocity fluctuations are in phase in the center of the mixing layer and out of phase for the points on the boundaries of the mixing layer.

Sediment Exchange between a River and Its Groyne Fields: Mobile-Bed Experiment

Experiments have been carried out in a mobile-bed laboratory flume in order to study the sediment exchange process between the main channel and the groyne fields. The flume represented half the width of a schematized river reach with a series of groynes. The experiment was designed to represent typical dimensions of the Dutch River Waal at a geometrical scale of 1:100. The conditions were set to guarantee bed load as well as suspended load sediment transport. Conditions with submerged and emerged groynes were investigated. In addition to traditional measurements, viz., bed-level changes, suspended sediment concentrations, and flow velocities, bed-form propagation was measured in two dimensions using a the particle image velocimetry technique. The results were analyzed with focus on sediment exchange mechanisms and sediment transport patterns. The results demonstrate that under all flow conditions there is a net import of sediment into the groyne fields. The prevailing transport mechanisms vary with the fl...

Fast response of lake plankton and nutrients to river inundations on floodplain lakes

AbstractKey variables in ecosystems tend to operate on widely different time‐scales. These time‐scales become relevant when a disturbance rocks the ecosystem. Here we try to explain the fast dynamics of plankton and nutrients in the water column of floodplain lakes after disturbances (inundations). We take advantage of natural experiments, that is occasional massive overflow of floodplain lakes with river water. We sampled 10 lakes in two floodplains along the Dutch river Waal monthly for 3 years, capturing the impact of three inundation events. The inundations reset the plankton as well as chemical composition of most lakes to largely the same state. While biologically inert macro‐ion data reflected a large and long lasting impact of the river water, dynamics of nutrients, phytoplankton and zooplankton communities between lakes diverged in a few weeks to regimes characteristic for the different lakes. While one spring inundation synchronized plankton dynamics to let the subsequent clear water phase occur at the same moment in different lakes, winter inundations did not have the same effect and apparently dynamics quickly diverged. Our results showed that effects of inundations and other processes that affect the state of the ecosystem should be studied considering the level of the slow components such as the sediment nutrient pool, fish stock and macrophyte communities. Plankton communities and lake water nutrient status give a practically instantaneous reflection of the condition of these slow components. Copyright © 2008 John Wiley & Sons, Ltd.