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Geul

The Geul rises in Belgium at about NAP +350 m and flows through places such as Kelmis, Plombières and Sippenaeken near Cottessen, where it enters the Netherlands. At Gulpen the larger tributaries such as the Gulp, Eyserbeek and Selzerbeek converge. Downstream the Geul flows via places such as Wijlre, Schin op Geul, Valkenburg and Meerssen into the Meuse at Bunde. The total length of the Geul is about 60 km and the size of the river basin is about 340 km², more than half of the basin is in the Netherlands.

© JCAR ATRACE

The Belgian part of the Geul river basin is characterised by a relatively rapid response to precipitation compared to the Dutch part of the basin. This is caused by the fact that in this part the soil is thin and lies on poorly permeable rocks. 

The catchment has a lot of grassland (46%), arable land (19%) and forest (20%), in addition to buildings (12%), roads (5%). The landscape thus comprises much rural area and rather little built-up area. Many towns and villages are located in the stream valley, where water regularly flows through a narrow village centre. These centres are therefore prone to flooding. To reduce the  the risk of flooding, throughout the catchment area - and especially in the tributary streams - many rainwater buffers have been constructed. These reduce discharge peaks. The rainwater buffers are mainly intended to absorb locally heavy rain showers (for recurrence times of about 10 to 25 years). 

Valkenburg is one of the locations where the stream flows through a town centre. The town lies in the floodplains of the Geul, about 10 km upstream of its mouth in the Meuse. Valkenburg is therefore one of known bottlenecks where flooding occurs when there is extreme precipitation throughout the Geul river basin. From the Geul river's perspective, the buildings in Valkenburg are obstacles, creating this bottleneck. This issue is less pronounced in the other villages along the Geul.

340

Square kilometers

300

Height difference

12%

Urban area

75.000

Buildings

Upcoming research:

In this river basin, JCAR ATRACE current focus is on (1) comparing different flood models and their capacity to quantify the impact of nature-based solutions on mitigating the consequences of extreme events (more info), (2) installing climate-robust water and debris monitoring systems (more info) and (3) effectiveness of flood adaptation measures at household-level (more info).

© JCAR ATRACE

Publications in this basin

What-if simulation in Flanders with precipitation July 2021 (Dutch)

This report describes what the impact would be if a water bomb such as the one that occurred in July 2021, and caused a lot of damage due to floods in Wallonia, would fall across the whole of Flanders. Two precipitation events are calculated for which hydrological and hydrodynamic calculations were carried out with the model instruments of the Hydraulic Engineering Laboratory. Flood maps were then calculated along the navigable waterways and damage calculations were made (report only in Dutch).
Belgium
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Watersystemanalysis Limburg 2021 (Dutch)

This analysis gives insights into the functioning of stream systems (Geul and Roer) during large amounts of precipitation in July 2021. Beside, the effects of different types of measures are described.
Netherlands
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Rapid assessment study on Geul river basin

In this study, an international team of researchers assessed the hydrological response of the basin to heavy rainfall during the summer 2021 event, the associated floodings and their consequences in order to find measures that are potentially suitable for the prevention of future floods impacts.
Netherlands
Belgium
Germany
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Hoogwater 2021 Facts and interpretation (Dutch)

In July 2021, large parts of Limburg were hit by heavy rainfall and flooding. Also parts of Belgium and Germany flooded, causing damage and loss of life. This was an extreme and unprecedented event with enormous impact. This exploration was carried out to take a first step to collect and analyze available information and knowledge about this event.
Netherlands
Belgium
Germany
Luxembourg
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Resilient Waterland - Weerbaar Waterland (Dutch)

Advice of the expert panel on flood protection to the Flemish government. With 'Weerbaar Waterland', the expert panel formulates an adapted strategy for water security in Flanders, with ten coherent actions and a plan of action to implement it as soon as possible.
Belgium
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Enhancing resilience: Understanding the impact of flood hazard and vulnerability on business interruption and losses

Thijs Endendijk et al. Water Resources and Economics https://doi.org/10.1016/j.wre.2024.100244
Netherlands
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Flood drivers and trends: a case study of the Geul river catchment (the Netherlands) over the past half century

Tsiokanos et al. NHESS https://doi.org/10.5194/hess-28-3327-2024
Netherlands
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Forestation can mitigate extreme floods in the Meuse basin

This research improves the hydrological simulation of the Geographical, Environmental, and Behavioural model (GEB) to better assess the impact of forestation on peak discharge in the Meuse basin. By incorporating a runoff delay function and in-situ measurements, the study shows that foresting the entire Meuse catchment could reduce the peak discharge of the 2021 flood event by 14.3%. Increased percolation and evapotranspiration were key factors in reducing pre-event soil saturation, allowing more water infiltration and less runoff during the flood. This demonstrates forestation's potential as an effective measure for mitigating future extreme floods.
Netherlands
Belgium
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Investigating the Implementation of Nature-Based Solutions in the Geul Catchment using Numerical Modelling

This research investigates the effects of different afforestation scenarios on flood risk in the Geul catchment using the SFINCS hydrodynamic model. Results show that afforestation reduces discharge proportionally to forest cover but has a limited effect on peak discharge for realistic scenarios. A delay in peak discharge was observed, which could aid flood preparedness. However, a flaw in the model's flood extent assessment suggests an underestimation of afforestation effectiveness. While SFINCS is effective for modelling flood extent, it is not recommended for assessing nature-based solutions.
Netherlands
Belgium
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Evaluating nature-based solutions for flooding in the Geul catchment using openLISEM

This study evaluates the impact of afforestation and hedgerows on flood reduction in the Geul catchment during the heavy rainfall of July 2021 using the openLISEM model. Results indicate that small-scale afforestation and hedgerows are ineffective in significantly preventing flooding, while full catchment afforestation can reduce peak flow by about 35%. The flood-mitigating effect of forests increases with forest age and is primarily driven by infiltration. Despite low flood mitigation impact, small-scale afforestation and hedgerows offer co-benefits such as carbon sequestration and biodiversity enhancement.
Netherlands
Belgium
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Neighboring basins

© Stefanie Wolf - RWTH Aachen

Roer
© Waterschap de Dommel

Dommel
© Waterschap Brabantse Delta

Brabantse Delta