River management has been practiced in the Netherlands for centuries, with groynes traditionally playing a key role. However, groynes do not provide a comprehensive solution to all challenges associated with rivers (Mosselman et al., 2021). Therefore, longitudinal training walls were introduced. These are long, narrow walls constructed parallel to the riverbank that divide the river into a main channel and a side channel. At high discharges, longitudinal training walls improve flood safety, while at low discharges they enhance navigability (Osorio et al., 2020). Because separate longitudinal water level profiles develop in the two channels, water levels within a cross-section can be different. Due to the porous nature of the training wall, these differences generate lateral flow between the main and side channel. This research investigates the following research question: How does lateral exchange between a main and side channel through a porous longitudinal training wall affect river water depth? This is particularly relevant during low discharge conditions, when minimum navigational depth is critical and lateral discharge towards the side channel may further reduce water depth in the main channel.