Can we elevate the subsiding coastal plain of the Netherlands with controlled sedimentation?

Abstract

Half the surface area of the coastal plain of the Netherlands has been subsiding below mean sea-level as a result of peatland drainage. At present, the low elevation is sustained, because sedimentation necessary to aggrade the coastal plain back to natural elevations is hampered by engineering structures. Alternatively, controlled sedimentation is a discussed method to elevate the coastal plain. This can either be achieved by allowing water courses to deliver sediments to designated areas, or by anthropogenic deposition.Here, we assess the possibilities of this strategy by determining whether natural systems or anthropogenic deposition are sufficient to elevate the surface to mean high water (MHW), taking into account IPCC projected minimum and maximum forecasted sea-level rise (RCP2.6 and RCP8.5), and predicted future subsidence. We use the 3D geological subsurface model GeoTOP to quantify sediments; i.e. clay and sand that were naturally delivered to the coastal plain by series of tidal inlets and the Rhine river system. Furthermore, we quantify the amount of anthropogenic deposition, and analyze documented supplies. Finally, we discuss the implications of controlled sedimentation in designated areas by providing examples of past embankment breaches.We quantify that 16.98 km 3 of sediments are required to elevate the surface to MHW, and between 22.41 and 29.29 km 3 at the end of the 21st century. We estimate that 45.30 km 3 of sediments were delivered by the tidal systems during 3000 years (52 % sand), 20.18 km 3 by the Rhine river system during 8000 years (29 % sand), and 3.59 km 3 of anthropogenic deposition.We conclude that the coastal plain of the Netherlands cannot be elevated to more safe levels with controlled sedimentation. Exceptions are areas proximal to tidal systems with high sediment yields. Anthropogenic deposition, combining natural sedimentation with supplied sediments, or allowing peat growth in inundated areas could be viable alternatives as well as.

Biogeomorphic feedback drives dune development along nourished coastlines

“…Draining wetlands to accommodate urban expansion is also a common practice, effectively removing an important buffer against tidal floods. Moreover, delta regions across the world are subjected to land compaction and subsidence due to groundwater withdrawal and, often simultaneously, experience reductions in the rate of sediment delivery from their rivers due to large-scale engineering infrastructures (Koster et al, 2020). Besides creating various other problems, these processes lead, in effect, to a relative rise in sea-levels and increasing flood risk.…”