The river Waal is part of an economic important transport-corridor that connects the ports of Antwerp, Rotterdam and Amsterdam to Germany. Ongoing processes such as (1) climate change, (2) large scale river bed erosion and (3) up-scaling of vessels threaten the future navigability of the river. This will lead to massive economic damages as taken in 2018 (Strengs et al., 2020). Canalisation of the river by means of weir-lock complexes is a considered by Rijkswaterstaat to improve inland navigation during periods of low discharge and prevent economic damages. This leads to the primary goal of this study; investigate the required lock capacity to provide smooth and reliable passage of the river Waal now and in the future. A literature review was conducted to assess the future development of the drivers of the worsening navigation conditions and to gain insight in market- and fleet developments. The developments in the drivers underline the urgency for measures. The development of the fleet navigating on the river Waal is characterised by up-scaling for the past 20 year. This trend is expected to continue the coming years. Future market developments are very uncertain due to the energy transition and the nitrogen crisis, making it very difficult to make accurate projections on future fleet intensities and compositions. Therefore a range of traffic intensities is used to characterise future fleets that encounter the lock complexes. The number and locations of the lock complexes is investigated by analysing available nautical depths and water levels along the river Waal for several stationary discharges at Lobith. Water levels are set up to a level such that navigation for all vessels (fully loaded) is possible. From a financial perspective it is most attractive to minimise the number of weir-lock complexes, however this is contrary to flood safety aspects on the river Waal. Installation of two weir lock complexes is considered plausible taking into account minimising the number of weir-lock complexes and flood safety. Vessel traffic simulations are conducted in SIVAK III to investigate the performance of multiple lock configurations in terms of average waiting time and service level. SIVAK III is able to simulate the passage of vessels at an individual level in a network of waterways and locks. A fleet analysis on a representative IVS data set is conducted to provide SIVAK III with fleet intensities, fleet mixes and arrival patterns. For the upstream (rkm 905) lock complex is recommended to use a lock complex with 4 chambers with dimensions 28.4x305m, but with in mind the option for a 5th chamber in the future. This lock complex is able to handle the current fleet +10% intensity within the considered requirements. A 5th lock chamber of the same size can handle an increased intensity of +30% including strong up-scaling effects. For the downstream lock complex (rkm 941) it is recommended to use a lock complex with 4 chambers and dimensions 25x330m. The lock complex is able to handle the current intensity +30%.

Prolonged droughts induced by climate change are a significant threat to inland shipping on Dutch rivers, particularly on the river Waal, a branch of the river Rhine. The anticipated shift to a more rain-dominated river, due to reduced meltwater from Alpine glaciers, may aggravate extreme low flow conditions, threatening the Waal's navigability. To improve the navigability in a rain-dominated river system, the Dutch government decided the transformation of the river Meuse into a confined river with seven weir-lock complexes. This study aims to compare the discharge regimes of both rivers to examine whether the river Waal turns into a rain-dominated system similar to the river Meuse, which may justify weir-lock complexes in the Waal as a potential solution. Analyzing 100 years of discharge data at Lobith, using the Pardé coefficient, shows that the characteristics of the Waal's runoff regime are shifting from a mixed-river towards a more rain-dominated river. Future climate projections indicate more pronounced extremes in runoff regimes, emphasizing the changing nature of the river Waal. While becoming more rain-dominated, the Waal's discharge regime is not expected to match the Meuse's before 2085.@en