PIANC Smart Rivers 2022

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Abstract : *(250~1000 words)

The Upper Sea Scheldt (Flanders, Belgium) is a part of the estuary which extents from the North-Sea in the Netherlands to the shipping locks in Ghent with a total length of 160 km. The Sigmaplan meets challenges on flood protection and nature development in this unique fresh water estuarine system. 
Cumulative effects of i) the autonomous morphological development of the estuary, ii) the further evolution as a consequence of realignments and dredging works, and iii) sea level rise, result in an increase of tidal dynamics and turbidity which affect both habitat and light climate, and finally hamper the ecosystem functions. Moreover it impacts the shipping function.
In order to better understand the system functioning and to prepare for counteracting these undesired evolutions De Vlaamse Waterweg, the waterway manager, has launched a study programme to investigate solutions and to prepare a vision for the future management of the river.
An extensive modelling instrument was developed coupling different state of the art modules into one model chain. This includes: hydrodynamic, sediment transport modelling, water quality (ecosystem), habitat and higher trophic level models, and real time navigation simulations. The developed instrument proved to be highly effective as it allowed to study (i) the interdependencies between the different functions which allowed for an integrated analysis and evaluation of measures, and (ii) the ability to assess the robustness of measures for climate change. 
Three different alternatives consisting of a combination of measures such as bend cut offs, depoldering with or without the introduction of flood or ebb channels, flood control areas with or without reduced tidal action, section widening and narrowing (by sediment disposal or groyne fields) have been investigated. A reference year 2050 was considered for a range of climate change scenarios in order to improve the understanding of the reaction of the estuarine system to such measures.
The investigated alternatives range from mild (only interventions in and along the navigation channel), over moderate (the latter complemented with a selection of measures in the valley) to extreme (the previous set with a maximum of measures in the valley). The simulation results demonstrate that depoldering is a very effective measure to contol the increase in tidal range (as a consequence of climate change and bend cut-offs). In addition, depoldering also has a very positive effect on the water quality and development of estuarine nature. 
The wide range of simulated alternatives and achievable effects for different intervention levels, allow the selection of measures to obtain a desired level of system resilience. As such the results form the backbone for the development of a future vision on estuary management, while the model instrument will continue to be used to study design alternatives and finetune measures. The vision aims at developing a sustainable and multifunctional estuarine system, compatible with the ambitions of both the waterway manager and its stakeholders. Already today, the gained insights from the modeling tool are put into practice by the installation and follow up of pilot projects, of which some examples will be presented.

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