The Dutch system of waterways, of which the River Waal is the largest, allows for transport of cargo via inland navigation. Inland navigation as a transport mode contributes to the Dutch GDP and is indispensable for the Dutch strategic position in international world trade. Because inland navigation is river-based, it is dependent on natural conditions. Recent periods of drought, such as in 2018, have led to major financial impacts in the Netherlands and Germany. Due to climate change, periods of drought are expected to be more frequent, longer and more extreme in the future. Given the importance of inland navigation, measures are sought after to counteract these effects of climate change. Canalization of the River Waal is a last resort infrastructural measure to gain control over water levels on the river. To date, it is unclear whether climate change will eventually make it necessary to canalize the river for the benefit of inland navigation. In addition, it is unknown on the basis of what considerations such a decision should be made. This research attempts to answer these questions.

To investigate the necessity of canalization due to climate change, first the impact of climate change on inland shipping is determined on three different levels. First the hydrological development including occurrence of (low) discharges and corresponding water depths. Second the impact on individual vessel's loaded draught and loading rate, based on least available water depths on the River Waal in climate scenarios. Third the corridor cargo transport capacity, based on the occurrence of (low) discharges and the cargo transport performance of inland shipping in the past 10 years during similar discharge events. The development of these elements are the considerations in the debate on necessity of canalization of the River Waal from a shipping perspective. Whether these developments support the necessity of canalization is studied by means of limits which, if exceeded, may argue canalization. For the river's navigation function, requirements on navigability were identified based on prevailing international waterway management regulations (CCNR and TEN-T) as well as on previous Dutch canalization projects on the River Meuse and Lower-Rhine. The limits are projected on the analysed future development of the River Waal under climate change, to identify if and when they are met.

The hydrological development of the River Waal is assessed based on future discharge projections at Lobith under climate change. A range in scenario's is described, with a low emission and wet climate scenario 'Ln' on one side and a high emission and dry scenario 'Hd' on the other. In an Ln scenario, the future occurrence of days with low discharges (<1800 m3/s) on average per year is similar to that of the reference scenario (past 30 years, 1990 - 2020). In contrast, an Hd scenario shows a steady increase in the days of low discharges until 2100 after which the trend stabilizes. Extreme low discharges <600 m3/s appear. Furthermore, the lowest annual discharge (generally speaking during summer) lowers to 1000 m3/s by 2150, which is 750 m3/s lower than in the reference scenario.

At Rhine Kilometer 885 near Nijmegen the lowest water depths occur. In an Ln scenario the number of days with low water depth (<2.8 meter) is similar to the reference scenario with 40 days, independent of time. In the Hd scenario the number of days with low water depth increases where <2.8 meter occurs up to 3x more as in the reference scenario and outliers of <1.6 meters appear, up to 10 days. The long term average lowest discharge during the year drops from 3.5 meters in the reference scenario to 3 meters in 2050 and <2.5 meters after 2100.

The analysis of discharges and water depths is used to describe the development of the transport function of the River Waal. The location with the lowest water depth on a route of a vessel determines the loading rate. The combination of loading rate and active fleet determines the total amount of cargo carried on a corridor. In an Ln scenario, there is little deviation from the reference scenario, but nonetheless, a large vessel 135x17.4 meter CEMT Class VI+ has a restricted loading rate for 7 months per year with a minimum of 50% of the maximum vessel loading capacity. In an Hd scenario the loading rate of vessels decreases and the period lasts longer. For a most common vessel 110x11.4 meter CEMT Class Va, an annual average minimum is observed of 60% in 2050 to 40% in 2150. The duration of restricted loading doubles and the steepest decline is observed between 2050 and 2100.

Based on historical performance (2010-2020) of inland navigation, linked to the occurrence of discharges, a first-order indication of the development of transport performance over the River Waal corridor under climate change is made. No absolute numbers can be determined on this basis, but a sense of trends can be obtained.

Assuming no changes in the current fleet, the annual total weight that can be transported will decrease regardless of the climate scenario. The severity does depend on the climate scenario. Zooming in on cargo type does show a varying picture, where for dry bulk cargo there is an annual decrease of -3.0% cargo transport capacity in the most severe 2150 Hd scenario, while for liquid bulk cargo there is a steady decrease to -12.0% cargo transport capacity in 2150. This difference is explained by the number of trips made, where for dry cargo this theoretically rises to +25% in 2150 Hd, while for liquid cargo it can only increase +3%. Redundancy in the fleet can thus partially counteract the effects of climate change.

To reason the necessity of canalization, limits on navigability are identified, based on current navigational requirements and previous canalization practice. For the river's transport function, no clear limits where found, as a result of which no development could be identified that necessitates canalization. There are two regulations that apply to the navigability of the River Waal. TEN-T is a transport policy of the European Union and sets requirements for the quality of its network. On the River Waal, a guaranteed draught of 2.5 meters is required year-round. This is not met in the present (20 days undershoot in an average year) and will not improve in any climate scenario (up to 80 days in 2150 Hd). The CCNR is an association of five countries that is committed to the safety and interests of inland navigation on the Rhine. CCNR guidelines are leading for river management in the Netherlands. On the River Waal, 'OLR' (Agreed Low River Level) conditions require a water depth of 2.8 meters in the fairway, per definition a water depth that is undershot on average 20 days a year. This is not met in the present (40 days undershoot in an average year) and will not improve in any scenario in the future (>100 days in 2150 Hd).

Conditions on the River Meuse (1920) and Lower-Rhine (1960) before canalization were projected onto the present River Waal. If, as on the River Meuse, one want to accommodate a normative vessel CEMT VIc 6-barge push barge, there is at least 180 days of loading rate restrictions, now and in the future under all considered climate scenarios. The Lower-Rhine is canalized for the purpose of navigability of Lower-Rhine and River IJssel and to control freshwater distribution. Both Lower-Rhine and River IJssel did not meet the navigability requirements set at the time. The River Waal also does not meet its current stated navigability requirements (CCNR 2.8m: 40 days), but even in the extreme 2150 Hd scenario this is roughly only half (100) of the days as on the River IJssel and Lower-Rhine (2.7m: 190 and 225). The navigability requirements of that time did fit better with the draught of a most common vessel. The current most common vessel 110x11.4 meter CEMT Va experiences as many days (160) of insufficient water depth as on the River IJssel in all dry climate scenarios between 2033 and 2050. Compared to the Lower-Rhine, this is the case in an Hd scenario between 2050 and 2100 (180 days).

This research concludes is that from the inland shipping perspective there are two overarching considerations in the decision on canalization of the River Waal, the perspective of the navigability of the river and the perspective of its capacity to allow cargo transport. The navigability, described in (low) discharges and water depth, deteriorates due to climate change. Clear thresholds as TEN-T and CCNR requirements are not met and there is not sufficient water depth to accommodate the normative vessel CEMT VI+ year round. Taking action in the form of canalization would guarantee these requirements to be met now and in the future. Uncertainty in climate conditions causes that no clear predictions can be given on how severe the impact on the transport function is. Furthermore the transport function is more complex, since it describes a spread of individual vessels, different cargo types and a corridor. It is not inconceivable that adjustments within the 'transport function', like alterations in the logistical chain or improvement of the fleet, could (partially) counteract the negative impacts of climate change, which subvert the necessity of canalization. Apart from that, this research concluded that for the transport function there are no uniform quantified goals. Goals mentioned are the added value to Dutch GDP, the role in other sectors, the model shift and (military) strategic. Since these goals are broadly formulated, but not well quantified, it is difficult to identify limits in the performance of the system under climate change which could argue the necessity of canalization. To make a deliberate decision on canalization based on its capacity to allow cargo transport, it should first be defined and quantified what achievements should be made with the River Waal.

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%.

This research focuses on the impact of extreme low river discharges, meaning discharges below 1200 m2/s at Lobith. In 2018 extreme low river discharges in the river Rhine led to congestions in the main Dutch part, called the river Waal. The river Waal is an important river for inland navigation, but during low discharges the vessel draught reduces and consequently the transported cargo volume per shipment reduces. To compensate the loss of transport volume, the total number of shipments increases, leading to an increased traffic intensity on the river Waal.  The purpose of this study was to investigate the effects of extreme low discharges on the traffic flow and traffic capacity in the river Waal. The study consisted of two elements: a study combining fleet data and hydraulic information and a traffic simulation study. During this research IVS90 data was used as the source for inland waterway transport data. Based on literature and previous river Waal studies the river section between the Pannerdensche Kop and the Maas-Waal canal was selected as the river section to investigate in more detail. Multi-beam measurements in combination with water level data were used to generate cross-sectional profiles in order to carry out the simulations. The cross-sectional profiles were highly variable. From these cross-sectional profiles the navigable river width was determined. It was found that a river depth of 2.80 m was no longer available at all cross-sections from a discharge of 900 m2/s and lower. Therefore, the navigable width was determined at a river depth of 2.0 m for the discharges 1020, 900, 800, 700 and 600 m2/s. Also, it was found that with reducing discharge the navigable width of the cross-sections reduced.   The fleet composition was determined in detail for four weeks representing the drought of 2018. These four weeks in 2018 represented weeks with average discharges around 1020(2x), 800 and 700 m2/s. The river Waal fleet composition was determined based on the Rijkswaterstaat vessel classification system (RWS-class) and categorised in three groups: coupled units (all RWS-classes with index C), push-tow units (all RWS-classes with index B) and motorised vessels (all RWS-classes with index M). It was found that the number of passages by coupled units and push-tow units was effected largely during the drought of 2018. The number of passages by push-tow units reduced significantly from October 2018 as the discharge dropped below 1500 m2/s and the number of passages remained low until the discharge raise above the 1020 m2/s at the end of 2018. The number of passages by coupled units increased already before the discharge reached the 1020 m2/s limit and continued to increase throughout the period of drought. The number of passages by coupled units started to decline only after the discharge rose above the 1020 m2/s again. Even though the daily average number of passages increased during the drought of 2018, the total transported cargo volume per day decreased. There was a strong relationship between discharges below 1200 m2/s and the transported cargo volume per day.  Within this study special attention was given to the occurrence of congestion in the river Waal. The occurrence of congestion was investigated using the traffic simulation model SIMDAS. As indicators for congestion a fluency and safety limit of 8% was used to evaluate the simulated traffic, as well as simulations of the traffic flow. As safety parameter the penetration of the safety margin of a vessel in percentage of the total number of vessel interactions was used. While the percentage of the number of vessels that need to reduce their speed fully during their passages was used as the fluency parameter. With SIMDAS also the impact of increased traffic intensity and reduced navigable width were analyzed. The simulation results showed that the reduced navigable width had more impact on the delay time, the fluency parameter and the safety parameter than the increase of the daily intensity. During the simulations large congestions occurred for discharges of 800 m2/s and lower, but small harmonically moving congestions already occurred for a discharge of 1020 m2/s. Harmonically moving congestions, meaning seven or more vessels traveling behind one larger or slower vessel while awaiting room to overtake, were observed in the traffic simulations. Permanent congestions with ten or more vessels were observed in the simulation of the river width with a 800 m2/s discharge. The data analysis and the traffic simulations clearly showed the effects of the extreme low discharges on the traffic flow and traffic capacity. The conclusion of this study is that the traffic capacity of the river Waal is at its limit at discharges of 800 m2/s and lower.  This study made also clear the need for correct fleet data and river bed levels. The limited available fleet data reduced the accuracy of the results. The river bed should be monitored regularly in order to know the actual water depth particularly during low discharges. Furthermore, it is recommended that highly variable river profiles are implemented in the traffic simulation model SIMDAS to improve the simulation of the vessel's sailing trajectories. Also, the validation of the vessel trajectories in SIMDAS with AIS data is recommended in order to evaluate the traffic intensity on the traffic lanes in the river.