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. The side channel was constructed with a sill at the upstream entrance (left side of the picture) and an unobstructed outflow at the downstream side (right side of the picture). (Source: Rijkswaterstaat).
Insights on the erosion and deposition effects of the longitudinal dams and rules of thumb for their design.
Due to climate change, more extreme river conditions will occur in the Netherlands but also abroad due to long dry periods and extreme discharge peaks. To mitigate these effects, longitudinal training dams are implemented in the inner bend of a 10 km river stretch in the Waal River. These dams aim at increasing the flow depth in the fairway or navigation channel during periods of low water levels and to decrease water levels during floods. Despite the fact that different kinds of longitudinal dam-like structures can be found in multiple rivers internationally (e.g. the Loire River near Chatillon sur Loire in France and the Main River near Karlstadt am Main in Germany), there is not yet in-depth knowledge on the way these structures regulate water and sediment flows. Erosion and deposition patterns in both fairway and side channel are important for river managers, as they might increase the need for dredging the fairway or limit the suitability of the side channel to be used by recreational boaters.
Key goals: Fundamental understanding Innovative monitoring
Physical scale model of the upstream section of a longitudinal dam (the arrow indicates the flow direction). Four sill geometries (in red) and field measurements of the bed in the Waal at the entrance of the side channel (Source: de Ruijsscher et al. 2018 and Rijkswaterstaat)
A scale model of the most upstream part of a longitudinal dam was built in a 2.5-metre-wide flume in the hydraulics laboratory in Wageningen. We used such model to get insights on the flow dynamics and its effect on the local patterns of the river bed due to the side channel intake. To mimic the river bed evolution realistically, polystyrene particles are used as surrogate sediment. To measure the erosion and sediment changes accurately, a measurement system consisting of a line laser scanner combined with a 3D-camera was built and tested. To optimize the longitudinal dam design, we focused in the local effect of the sill geometry at the side channel intake. Therefore, we carried experiments with four sill geometries: A) uniform low, B) downstream increasing, C) downstream decreasing, and D) uniform high sill height. An existing dataset of bed level measurements in the Waal River (from regular river maintenance) is analyzed to study the effect of the longitudinal dam construction on the river bed dynamics. We are comparing the resulting bed data of the lab measurements with the field dataset.
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
A line laser scanner is developed and tested, which 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 a scale model study on the local hydraulic and morphological effect of LTD inlet design. The main result is that the side channel discharge is mainly determined by the cross-sectional area over the sill, and that a downstream decreasing sill height results in a morphologically dynamic system. Whether this is feasible or not depends on the needs of different purposes of the side channel, e.g. ecology and recreational boating.
From morphological analysis in the Waal River, it turns out that bed forms of different length scales co-exist: dunes and forced bars. In general, dunes cannot be treated separately without taking into account the bars, because both dune height and length correlate with the location on the bar.
Status for day-to-day practice
This section will be available as soon as possible.
Location along the 10 km stretch of the river Waal (between Tiel and Ophelmert) in which the longitudinal dam pilot was implemented.
Spatial scale: River section
Key locations: Waal River (NL)
This section will be available as soon as possible.
Last modified: 11/02/2019
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.
Anything to ask or share?About us
We would like to learn from your experiences and questions to take our knowledge further into practice in the Netherlands and abroad. Your feedback will help us to find out about your interests and how useful the information provided was to you.