Heavy rainfall and cross-border dam failure can result in extreme flood waves. Climate change increases the frequency and intensity of extreme rainfall events, which can push hydraulic structures such as dams to their limits. Potential failure can lead to severe flooding that is rarely accounted for in flood risk planning, particularly if the structure in question is located abroad. This study assesses the consequences for the Netherlands of extreme flood waves in the Rur river. To model flood propagation, a new hydrodynamic model was developed, for the Dutch section of the Rur river basin. Several synthetic hydrographs were implemented as upstream boundary condition at the Dutch border. First, two different hydrographs were generated representing extreme flood waves. One with a peak discharge of approximately 900 m3/s and a total cumulative volume of approximately 22 million m³, called the Large Flood Wave (LFW) and one with a peak discharge of 10000 m³/s and a cumulative volume of 143 million m³ named the Massive Flood Wave (MFW). Presenting two different extreme hydrograph scenarios. To see if the shape of the hydrograph results in different outcomes these hydrographs are flattened. Three scenarios per dam are evaluated: the original hydrograph (LFW and MFW 100% peak discharge) and two reduced scenarios where the peak discharge is scaled to 75% and 50% of the maximum peak. The total flood volume remains constant for all scenarios.
Determining direct economic damage. From the Dutch border to Roermond (≈ 19 km) the arrival time of the Large Flood Wave is 22 hours. Due to attenuation across the wide floodplain, the peak discharge is reduced to 161 m/s in Roermond. A sensitivity analysis indicated that increasing the initial Rur river discharge from 21.43 m³/s (average discharge) to 129.35 m³/s (flood discharge) reduces the arrival time from the Dutch border to Roermond to 12 hours, halving the arrival time. This significant difference is driven by the ’wet-bed’ effect. The Massive Flood wave reaches Roermond in 5 hours, attenuating to 3204 m³/s and causing flooding in Roermond. The resulting peak discharge in the Meuse river, just downstream of Roermond, reaches 2888 m³/s, remaining slightly below its design discharge of 3275 m³/s. The consequences for the Netherlands depend heavily on the peak discharge and volume of the flood wave hydrograph. The flooding caused by the Large Flood Wave would largely be confined to the Rur river floodplains, causing minimal urban flooding. However, direct economic damages is still estimated to approach 90 million euros, primarily due to rail and road infrastructure. Massive Flood wave flooding would have catastrophic consequences: floodwaters would extend far beyond the floodplains. The direct economic damage is estimated at 1.4 billion euros. These findings underscore the critical need for cross-border flood risk management. In particular, the implementation of an early-warning system, to ensure that residents can evacuate timely.
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