Flood modelling in transnational rivers requires efficient cross-border collaboration among the riparian countries. Currently, each country/region usually uses a different hydraulic modelling approach, which may hinder the modelling of the entire river. For the sake of accurate and consistent river modelling there is a necessity for the establishment of a framework that fosters international collaborations. This study investigates the current hydraulic modelling approach across the whole length of the River Meuse, the main course of which crosses three north-western European countries. The numerical models used by French, Belgian, and Dutch agencies and authorities were interconnected by exchanging boundary conditions at the borders. At the central part of the river, the Belgian hydraulic model assumed steady flow conditions, while the rest of the river was modelled in unsteady mode. Results for various flood scenarios revealed a distinctive pattern of water depths at the Belgian-Dutch border. To clarify whether this is a bias induced by the change in modelling approach at the border (steady vs. unsteady), we remodelled a stretch of the river across the Belgian-Dutch border using a consistent unsteady modelling approach. The steady and unsteady approaches led to similar patterns across the border, hence discarding the hypothesis of a bias resulting from a change in the employed model. Instead, the pattern in water depths was attributed to a change in the topography of the Meuse Valley, where there is a transition from a narrow steep corridor with limited water storing capacity in Ardennes massif to wide floodplains in the Dutch lowlands. The associated flood damping for the 100-year discharge is less than 1% in the Ardennes and exceeds 15% in the Dutch lowlands. It can be inferred that the current differences in regional hydraulic modelling approaches for the River Meuse are generally well-grounded and not just a legacy of the past.

跨国河流的洪水建模要求沿河国家之间进行有效的跨界合作。当前，每个国家/地区通常使用不同的水力建模方法，这可能会阻碍整个河流的建模。为了准确和一致的河流建模，必须建立一个促进国际合作的框架。这项研究调查了整个默兹河全长的水力模拟方法，该方法的主要过程跨越了三个西北欧洲国家。法国，比利时和荷兰机构和当局使用的数值模型通过交换边界条件相互关联。在河流的中部，比利时的水力模型假设流量稳定，而河的其余部分则以不稳定模式建模。各种洪水情景的结果表明，比利时-荷兰边境的水深具有独特的模式。为了阐明这是否是由于边界建模方法的变化（稳定与不稳定）引起的偏差，我们使用一致的非稳定建模方法对跨越比利时－荷兰边界的一段河段进行了建模。稳定和不稳定的方法导致跨边界的相似模式，因此放弃了因所采用模型的变化而导致的偏差的假设。取而代之的是，水深的变化是由于默兹河谷地貌的变化而引起的，那里的变化是从狭窄的陡峭走廊到阿登山脉的有限储水能力，再到荷兰低地的漫滩。对于100年排放，相关的洪水阻尼在阿登地区不到1％，在荷兰低地地区超过15％。可以推断出，默兹河区域水力建模方法的当前差异通常是有根据的，而不仅仅是过去的遗留问题。