In his 2019 National Day Rally speech to the nation, Prime Minister Lee Hsien Loong addressed the pressing concern of climate change and sea level rise. PM Lee outlined a S$100 billion plan over the next century to protect Singapore against sea level rise which includes planting and managing mangrove coasts, or engineered options like sea walls, land reclamation and polders.
Current climate projections predict a 1m sea level rise by 2100. Much of Singapore lies only 15m above the mean sea level, with about 30 percent of the island less than 5m above the mean sea level.
While 2100 remains in the distant future, such a long-term view would give Singapore ample time to implement and execute a long-term solution. Construction of a comprehensive sea defence is no easy feat and this endeavour would likely span several generations. However, as Singapore looks to holding back the sea, there are historical examples of countries who have successfully done just that.
Netherlands’ sea defences
About one third of the Netherlands lies below sea level, with the lowest point being 22 feet (6.7 meters) below sea level. Meanwhile, the highest point is about a thousand feet above sea level.
Given its low elevation, flood control is a major issue in the Netherlands. The country relies on an extensive network of natural sand dunes and constructed dikes, dams, and floodgates to hold back storm surges from the sea. Netherlands’ sea defences have played such a pivotal role in the country’s development that without them, major cities like Amsterdam, Utrecht, and Lelystad would not have existed.
500BC to 700AD
Netherlands’ sea defences date back several millennia. The earliest indications of dike building date from the late Iron Age. Excavations of terps in the Frisian villages of Peins and Dongjum, uncovered small dike bodies. These little dikes, no more than 70 cm high, were composed of neatly-stacked peat sods against a core of loose bulk material. Later on the structure was reinforced by adding an outer wall with a gentler gradient.
700AD to 1200AD
The eighth century saw renewed population growth, after which the population of the Netherlands increased tenfold between 800 and 1250. To accommodate the growing number of settlements, streams were dammed and low dikes built, following the contours of the existing differences in elevation.
1200AD to 1500AD
The fourteenth century saw the first large-scale building of dikes. The population was falling in some parts of Europe, as a result of economic recession and pandemics like the Bubonic Plague, but the Netherlands, was doing relatively well.
1500AD to 1800AD
The sixteenth to nineteenth centuries saw accelerated population growth and rapid economic development. Large-scale hydraulic engineering works such as land reclamation, polders and large-scale peat extraction were organized by collectives, with interested parties joining forces for the purpose.
In 1730, the advent of the naval shipworm saw the Netherlands’ dikes and wooden structures being eaten away by a mollusc that thrived in the country’s climate. In reaction, efforts were made to find alternative materials and dike designs.
1800AD to 1950AD
By the nineteenth and twentieth centuries, dike builders had switched to constructions with low-gradient outer slopes. Stones were also added to the dikes to further strengthen them. From the twentieth century onwards, concrete blocks were developed, mass-produced and transported to dike construction sites. The advancement in technology and the road network made large-scale interventions in coastal defences possible.
The largest hydraulic engineering project undertaken in the twentieth century was the Zuiderzee (Southern Sea) works. The project involved the damming off of the Zuiderzee, a large, shallow inlet of the North Sea, and reclaiming land in the newly enclosed water body by means of polders. Its main purpose was to improve flood protection and create additional land for agriculture. This resulted in an additional 1000 square kilometers of land being reclaimed for construction. In 1986, much of this reclaimed land constituted the new Flevoland province.
1950AD to present
In 1958, the Dutch Parliament authorized the Delta Plan – a large network of hydraulic works to seal off sea inlets making the coastline shorter and easier to defend. The Delta Plan prescribed the criteria to be met by the dikes along the coast and rivers as well as their height.
By the 1980s, environmental activism brought to light the adverse effects of excess damming of water bodies. The policy document ‘Ruimte voor de Rivier’ (‘Space for the River’) advocated widening the riverbed instead of another large-scale reinforcement of the dikes.