Aerial photograph of the intake of a longitudinal training dam in the Dutch Waal River which divides the river into a side and main channel. (Source: Rijkswaterstaat).
Insights on the erosion and deposition effects of the longitudinal training dams, as well as on the detailed flow patterns at the side channel intake.
More extreme river conditions will likely occur in The Netherlands, for instance, longer dry periods and more extreme discharge peaks. To mitigate these effects, longitudinal training dams have been implemented in the inner bend of a 10 km river stretch in the Waal River (see Figure). The purpose of these dams is to increase the flow depth in the navigation channel during low water levels and to decrease high water levels. Despite the fact that longitudinal dams can be found in different forms in multiple rivers internationally (e.g. the Loire river in France and the Main River in Germany), there is not yet in-depth knowledge on how these structures regulate water and sediment flows. Erosion and deposition patterns in both the navigation and side channel are important for river managers, as they might increase the need for dredging on the main channel or limit the suitability of the side channel to be used by recreational boaters.
Key goals: Fundamental understanding Innovative monitoring
A scale model of the most upstream part of a longitudinal training dam was built in a 2.5-meter-wide flume in the Kraijenhoff van de Leur Laboratory for Water and Sediment Dynamics at Wageningen University & Research. We used this model to get insights on how the flow pattern affects local erosion and deposition patterns. To mimic the river bed evolution realistically, we used polystyrene particles as surrogate sediment. To measure the erosion and sediment changes accurately, we built and tested a line laser scanner consisting of a line laser combined with a 3-D camera.
A physical scale model is used to study the effect of the upstream sill geometry on flow division and sedimentation/erosion. Four geometries of the intake sill (in red) were studied. In the field, an extensive morphological dataset is used containing dunes and bars. (Source: adapted from de Ruijsscher et al. 2018)
To optimize longitudinal training dam design, we focused on the local effect of the geometry of the sill at the side channel intake. Therefore, we carried out experiments with four inlet geometries (see Figure): A) uniform low sill, B) sill with downstream increasing height, C) sill with downstream decreasing height and D) uniform high sill.
An existing dataset of bed level measurements in the Waal River is analyzed to study the effect of the longitudinal training dam on the river bed dynamics. The resulting bed level data is not only used to verify the results of the laboratory experiments but also to study the effect of longitudinal training dams on bedforms on different spatial scales (dunes, bars).
In order to understand the flow patterns at a side channel intake, measurements were carried out with ADCPs (acoustic Doppler current profilers). Measurements with vertical ADCPs were carried out at different water levels to capture the spatial variation in flow velocities. Continuous measurements with two horizontal ADCPs on the upstream sill were carried out for over a year to capture the temporal variation of the flow over the sill.
For whom and where?
The general results can be used by river managers on the river reach scale. Laboratory methods like the line laser scanner can be used in hydraulic laboratory studies with the movable bed. Advisors studying the classical situation of flow and bedload transport over an oblique weir can also benefit from the results for this specific setting.
Data-collection methods: Field survey measurements Physical and laboratory experiments Remote sensing
Temporal scale: Seasonal measurements
Application and findings
The line laser scanner allows for accurate monitoring of the bed evolution in laboratory experiments with moving bed, even under flowing water conditions. This technique is later used in the scale model to study the local hydraulic and morphological effects of the geometrical design of the side channel intake sill. The fraction of the total river discharge flowing into the side channel is mainly determined by the cross-sectional area over the sill (i.e. inlet geometry). A too small sill height cause s a too large side channel discharge, under which condition the design requirements are not met. Moreover, a downstream decreasing sill height results in the morphologically most dynamic system. Whether this is also the most favorable design depends on the needs of different purposes of the side channel such as ecology and recreational boating.
From the morphological analysis in the Waal River, it turns out that bedforms of different length scales co-exist: dunes and hybrid bars. In general, dunes cannot be treated separately without taking into account the bars, because both dune height and length correlate with the location of the bars. The construction of longitudinal training dams leads to a change in the location of the bars. However, the statistical properties of the dune characteristics do not change.
Over a small part of the intake sill, reverse flow from side to the main channel is observed, pointing at some kind of recirculation (work in progress).
Status for day-to-day practice
Currently, the outcomes are specific for the pilot in the Waal River. For application in different settings, careful consideration of which processes are dominant is important.
Location of the 10 km stretch of the Waal River (between Tiel and Ophemert) in which the longitudinal training dam pilot was implemented.
Spatial scale: River section
Key locations: Rhine River (NL) Waal River (NL)
To be able to use the knowledge efficiently for future constructions of longitudinal training dams, implementation of longitudinal training dams in numerical models and testing against observations is important.
Last modified: 19/06/2019
Explore the contact details to get to know more about the researchers, the supervisory team and the organizations that contribute to this project.
Timo de Ruijsscher
Wageningen University & Research
As soon as available, explore the storyline to get to know more about the main methods or prototype tools that were developed within this project.
Explore the output details for available publications to get a glance of the innovative components and implications to practice as well as the links to supporting datasets.
Morphological patterns at the intake of a side channel over an oblique sill
Application of a line laser scanner for bed form tracking in a laboratory flume
Take a look to the dissemination efforts and application experiences which are available in the news items and blogs.
Collaborative monitoring or longitudinal training dam effects in the Waal River
15/07/2018 by prof. dr. Suzanne Hulscher
RiverCare is part of 'WaalSamen', a collaborative group to measure and compare the effects of the longitudinal dams as an alternative to river groynes.
ITV Border Special Report: Living with the River
18/02/2016 by dr. ir. Ton Hoitink
British TV visited the longitudinal dams pilot in The Netherlands, to find out about how the Dutch better protect their communities from flood in...
Brochures about the longitudinal training dams
19/03/2018 by Laura Verbrugge
Communication of project results is important to enable the exchange of knowledge between the different stakeholders affected by the river intervention in the case...
Citizen Science newsletter editions of a participatory monitoring project
01/12/2017 by Laura Verbrugge
Monthly newsletters during the fishing season and a Facebook page update participants of the ongoing activities and results.
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