Landscape and Geomorphology

The situation of the Rhine, Meuse and Scheldt Delta is defined by the transport of river sediments, combined with strong tidal movements and sea currents. As a result of these conditions a delta is formed with a sand barrier coastline of beaches and dunes in front of the alluvial wetlands. The Dutch coastline has been formed of marine sediments. These sediments are mainly transported by the dominant Gulf Stream and tidal currents. Over many centuries the western part of the Netherlands was covered in a thick layer of peat (4 to 6 metres). This peat landscape was interwoven with a network of creeks and small rivers functioning as a natural drainage system. As a result of this the delta can be defined as sea dominated (Meyer & Nijhuis, 2014).

Urban development

The sea inlets in the delta offered new opportunities for trading routes and for the discharge of the drainage systems. To be able to profit from these opportunities a complete reorientation of the drainage system and the spatial structure of the urban system was necessary. It was also necessary to create a defence against flooding. Land owners and local communities started constructing drainage systems to reclaim the swampy peat lands. A result of this new drainage technology was drastic subsidence. Some parts of the deltaic area even subsided eight metres, resulting in land five to six metres below mean sea level. The central part of the Netherlands (Randstad) was transformed from a wet lagoon into a drained and rationalised landscape, surrounded by levees (Meyer & Nijhuis, 2014).

Sediments

The situation in the Dutch Delta in the early 19th century can be regarded as a mosaic of polders that had transformed most of the alluvial wetlands into an engineered landscape. The natural dynamics of the landscape were used as the fundament for new infrastructural networks such as levees and drainage canals, developed in combination with new urban structures. As a result of this however, was that the river channels and estuaries of the delta were narrowing and silting up because of the on-going process of sedimentation. This combination caused the Dutch rivers to flood frequently because of the lack of discharge possibilities during extreme supply of water. The rivers and estuaries also became too shallow for modern navigation due to the sedimentation (Meyer & Nijhuis, 2014). However, since the 1980s, as a result of anthropogenic intervention, the RMS Delta has shown a negative sediment budget (more outgoing than incoming sediment). Following a large offshore port expansion, dredging in ports and harbours in the delta has doubled in the last years. In addition, the deeper navigation channels, ports, and harbours are now trapping siltier sediment, changing the sediment composition in the mouth (causing change in the ecology). The removal of sediment by dredging is adverse to the necessity for sediment in heavily eroding branches (Cox et al., 2021). The Dutch delta currently faces the problem of rising sea levels, extreme peak discharges and an eroding coast (negative sediment balance), partly due to climate change. To battle these problems the Dutch came up with a plan called “ruimte voor de rivier” (space for the river). The “space for the river” project focuses on two important benefits: safety and spatial quality. As the name suggests, this project is designed to give the rivers more space so that they become more resistant to flooding. By giving the rivers more space you can counteract several problems, such as extreme peak discharges (water has more time to drain away) and eroding areas (sediments have more time to settle) (2005).