The Rhine, Meuse and Scheldt flow into the sea in the Southwest Delta. After the disastrous floods of 1953, the Delta Works brought flood risk management in this area up to the required standard. The dams and storm surge barriers have shortened the coastline considerably. That has led to the creation of a range of water basins: fresh and salt, with and without tides. The area is faced with a number of complex agendas in the areas of flood risk management, fresh water and spatial planning. These agendas result, in part, from climate change. A preferred strategy has therefore been established for this area as part of the national Delta Programme.
The implementation of the preferred strategy is proceeding as planned. There is considerable administrative ambition, and experience has been acquired in recent decades with pilot projects and living labs. There is a clear agenda in the short term for each sub-area. In addition, a network has been established with the focus on collaboration. This will be scaled up in the next five to ten years: conceptual options are being worked out in practical terms at the local level.
The Delta Works are causing new problems: the erosion of areas outside the dikes and problems with water and soil quality. Almost every year, there are blooms of blue-green algae in the fresh water of the Volkerak-Zoommeer because of excessive levels of nutrients and the inadequate flushing of the lake. The Binnenschelde and Markiezaatsmeer, which have been isolated by the Delta Works, also have recurrent annual problems with water quality. The bed of the Grevelingenmeer lake is devoid of oxygen in the deeper parts because of inadequate water circulation. Due to erosion, sand is constantly being lost from the sandbanks in the Eastern Scheldt (in a process known as the ‘sand starvation’ of the channels).
Oxygen depletion in the summer in the Veerse Meer lake is extending to shallower water. That resulted in mass fish deaths in the summers of 2019 and 2020. Leisure visitors are bothered by algae and clinging jellyfish in the summer. At present, despite the measures that have been taken, the nature objectives in the Water Framework Directive and Natura 2000 have not been met for the Veerse Meer lake or the other large waters in the Southwest Delta.
These problems have negative effects on the sustainable development of the regional economy. In addition, there is a risk of a mismatch between freshwater supply and demand because of the effects of climate change, in part as a result of salinisation and an increasing shortage of water during the growing season. Sea level rise will generate new risks in the area of flood risk management. These risks are extensively explored in the Sea Level Rise Knowledge Programme.
As part of the national Delta Programme, an integrated preferred strategy has been drawn up for the Southwest Delta. This strategy defines objectives and measures for maintaining flood protection, proper ecological functioning, and the user functions in the area. For the freshwater component, a supplement to the ongoing Freshwater implementation programme was drafted in 2021. The supplement consists of new and additional measures.