In densely populated areas (e.g. Japan, Taiwan or the Netherlands) it is becoming increasingly complicated to find large open areas at the mainland to start new developments (e.g. for a new airport, hosting new industries or even housing the growing population).
The open sea in front of the existing coast may be used to build an artificial island. In the Netherlands, for instance, there has been ongoing discussion on whether it is useful to build an artificial island off the coast near IJmuiden for hosting an extension of Schiphol Airport. A specific airport-island requires rather large dimensions (amongst others due to the length of runways). A typical size for such an island is 5 km. With respect to the distance of an island from the existing coast, an optimum has to be found taking into account transportation requirements, noise limitations and morphological implications.
An artificial island in open sea has large morphological implications for the existing coasts and affects the stability of coasts in a wide area. In the shadow area behind the island the wave characteristics will fundamentally change. Another aspect of an airport-island is that the (tidal) current patterns will be affected in the vicinity of the island. The adaptation time of the existing coastal area is generally relatively long. The water depth off the coast of IJmuiden, where such an island would probably be built, is approximately 15 m. Because of this depth, the required dimensions of an island and the required level above MSL (approximately 5 m) huge volumes of sand are required to construct such an island (order of magnitude 600 million \(m^3\) of sand.) These volumes are easily available from the bed material of the North Sea, but call for large borrow pits which also impact the morphology.
During dredging operations also fine-grained silt (see Sect. 2.6.2) will be mobilised, since within the sand deposits at the seabed often small volumes of silt occur (say 2 %). With a required volume of 600 million \(m^3\) and 2 % silt, this results in 12 million m3 of silt that is mobilised in the North Sea environment. The associated turbidity can have large ecological effects.
It is clear that in the final decision whether to build an artificial island or not, coastal morphology topics have to play a role.