Design of an adaptive weir

Abstract

In contrast with other Dutch rivers parts, human measures in the upstream part of the River Meuse did not mainly focus on discharging surplus water, but on retaining water in dry periods. Almost 100 years ago seven weirs were constructed in the River Meuse to enable transport of coals. The structures reach, due to concrete degradation, the end of their technical lifetime and the manual operation does not meet the current ARBO-legislation; both make replacement of the weirs required. Rijkswaterstaat, asset owner of the waterways and weirs, invited the civil engineering sector to collectively develop weir replacement strategies in 2015. The future developments of the river and surroundings were an important subject during the meetings. With this in mind, during the co-creation meetings under the title ‘Grip op de Maas’, one of the proposed weir replacement strategies was called the Adaptive Meuse (De Bouwcampus, 2015). This perspective took the future uncertainty into account by proposing adaptive designing of the weirs. This study builds on this perspective by the objective of designing an adaptive weir in the River Meuse according to the approach of adaptive delta management.This approach states that designs have to be flexible and able to switch between multiple strategies for future challenges concerning flood safety and freshwater storage. In this study, an overview of the measures required to deal with the development of specific purposes is provided by adaptation schemes. When and if a specific purpose applies, depends on which of the four Dutch delta scenarios, DRUK, STOOM, RUST and WARM, evolves. These scenarios are based on a unique combination of the rate of climate change and socioeconomic developments (Wolters, Van den Born, Dammers, & Reinhard, 2018). Adaptivity is obtained by regional adaptation measures over a particular stretch of the river and by weir adaptation measures. To address both the adaptivity of the river and the weirs, three design levels have been established. These levels are summed below:The global design level comprises the total dammed section of the Dutch River Meuse and two weir sections in Belgium. The series of weirs in the river still suffices the requirements; on this scale, no large adaptations have to be made now or in the future.The regional design level comprises the weir sections Roermond and Belfeld, since the adaptivity of these sections is the largest of all weir sections in the global design area.The local design level addresses the geometric design of weir Belfeld itself. The adaptivity of the designed weir enables the discard of regional adaptation measures with undesired implications.Since both dehydration and permanent flooding of the river valley have to be prevented and the water distribution over Belgium and the Netherlands is fixed in an agreement, the global adaptivity is limited. Weir removal or replacement of the current weir by a new weir at a different location is in most weir sections infeasible. Weir section Roermond forms an exception, since the commercial navigation uses the later dug parallel Lateral Canal, part of weir section Belfeld. Thus, the majority of weir section Roermond can be restricted to only recreational vessels. By modifications of weir Belfeld, it could possibly (partly) take over the functions of weir Roermond in future. In 2030 however, one-to-one weir replacement is selected to avert significant changes in groundwater table.For the regional design level, the future developments are split into the flexibility to groundwater changes, the use of freshwater for drinking water production, agriculture and industrial activities, the discharge of flood waves and the navigation on the River Meuse and to the port of Roermond. An adaptation scheme indicates what regional adaptation measures and weir adaptation measures are required to serve the purposes per time period in each of the four delta scenarios. On basis of this adaptation scheme, it is concluded that by designing an adaptive weir, measures along the entire weir section, for instance raising embankments or raising bridges, can be discarded in the future. The freedom of choice of the future waterway manager is preserved by an adaptive weir. In the last design level, an adaptive weir is proposed to replace weir Belfeld. The requirements to and the design of the adaptive weir are based on the regional adaptation scheme. The weir can be adapted by:constructing additional weir openings at the eastern embankment, enabled by the location of the new weir, which is just a couple of hundreds meter upstream of the current weir.adjusting the management of the weir gates, enabled by the choice of radial gates. The location in the weir section at which the dammed water level is independent of the river discharge can be shifted throughout the weir section. This allows the air clearance and the water level dynamics to be managed for container transport and ecological development, respectively. heightening the dammed water level, also enabled by the choice of radial gates. To withstand the larger water head, the initial investment increases by 30%. However, regional measures are saved in the future. Only the gates and height of the superstructure have to be adapted in the future to heighten the dammed water level.In conclusion, on global level, a change of the locations and numbers of weirs in the River Meuse is presently not desired and required, since the functions are met with the current weir layout. To guarantee this in the entire upcoming century, adaptations are required in the weir section Belfeld in the River Meuse. The resulting adaptation scheme after construction of the proposed adaptive weir presents the regional and weir adaptation measures that serve the mentioned scenario-dependent purposes. By the large adaptivity of proposed weir design, regional adaptation measures along the river with undesired implications can be discarded or minimized. Only if higher container vessels have to be accommodated on the Meuse River or the accessibility of the Prins Willem-Alexanderport has to be improved, regional measures are inevitable. The method used in this report can be used to set up adaptation schemes for all weir sections in the River Meuse. By involving Rijkswaterstaat and other stakeholders, the schemes can be turned into quantitative ones. Last, it is recommended to start structural calculations on the adaptive weir Belfeld.