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

Abstract

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.

Scale model of a training dam using lightweight granulates

“…Here, we report on a completed study in a laboarotory setting [1], focussing on flow and morphodynamics in the transition from a series of groynes to an LTD. In a companion paper [3], ongoing experiments are being presented for an LTD constructed at a local widening of a river.…”

Human intervention in rivers

“…We conclude that the presently available observations could not independently corroborate or verify model predictions. (Collas et al, 2018;De Ruijsscher et al, 2018) and other interventions Straatsma and Kleinhans, 2018). Decision making regarding the design of these spatially complex interventions was to a large extent based on model simulations (Klijn et al, 2013).…”

“…Intervention modelling may further be extended by including (stochastic) processes like vegetation growth ( Van Oorschot et al, 2015), morphodynamic development of interventions (De Ruijsscher et al, 2018;Van Denderen et al, 2019) and maintenance strategies Bout et al, 2019). It is unknown whether including such autonomous effects to predict the evolution of interventions, and their effect on multisectoral indicators, will result in a 'prediction horizon' beyond which model predictions are too uncertain to be useful for decision making.…”

“…Tot slot passen we de ontwikkelde methoden toe op een langjarige studie van Ruimte voor de Rivier, om te zien of modelvoorspellingen overeenkomen Introduction 1 1.1 Background FOLLOWING THE EVACUATION of more than two hundred thousand people from the Dutch Rhine delta in January 1995, the Dutch government decided in favour of a large scale overhaul of the Rhine river system (Rijke et al, 2012;Fliervoet et al, 2013). This flood prevention programme (Room for the River) consisted of 39 coordinated interventions in the Dutch Rhine Branches (Figure 1.1), such as side channels (Van Denderen et al, 2019), and longitudinal training dams (Collas et al, 2018;De Ruijsscher et al, 2018). These efforts built on river engineering from the previous century.…”

Side channel dynamics

“…This an important objective of the RiverCare Programme in which we evaluate the development of interventions at intermediate and longer time scales, and their consequences on various river functions (Hulscher et al, 2014;Augustijn et al, 2018). This includes evaluating the development of interventions (e.g., longitudinal dams (Collas et al, 2018;De Ruijsscher et al, 2018), the construction of side channels, the removal of bank protection (Duró et al, 2018a;, re-meandering of streams (Candel et al, 2018), creating new methods for evaluating such interventions (e.g., Berends et al, 2018;Chavarrías et al, 2018), and communicating the results to a wider audience (e.g., Cortes Arevalo et al, 2018;Den Haan et al, 2018). It is unknown how these interventions develop and affect the river and its functions over time.…”