Sea defences

Coastal management is defense against flooding and erosion, and techniques that stop erosion to claim lands.

Coastal zones occupy less than 15% of the Earth's land area, while they host more than 40% of the world population. Nearly 1.2 billion people live within 100 km of a shoreline and 100 m of sea level, with an average density nearly 3 times higher than the global average for population. With three-quarters of the world population expected to reside in the coastal zone by 2025, human activities originating from this small land area will impose heavy pressure on coasts. Coastal zones contain rich resources to produce goods and services and are home to most commercial and industrial activities.

In the European Union, almost half of the population lives within 50 kilometres of the sea and coastal resources produce much of the Union's economic wealth. The fishing, shipping and tourism industries all compete for space along Europe's estimated 89,000 km of coastline and coastal zones contain some of Europe's most fragile and valuable natural habitats.

Protection against sea level rise in the 21st century will be especially important, as sea level rise accelerates. Changes in sea level damage beaches and coastal systems. Coastal sediments are disturbed and suspended by wave and tide energy.

Coastal engineering of harbours began with the origin of maritime traffic, perhaps before 3500 B.C. Docks, breakwaters and other harbour works were built by hand, often in a grand scale.

Ancient harbour works are still visible. Most of the grander ancient harbor works disappeared following the fall of the Western Roman Empire.

Most coastal efforts were directed to port structures. Venice and its lagoon is an example of measures not related to ports. Protection of the shore in Italy, England and the Netherlands began in the 6th century or earlier. The ancients understood phenomena such as Mediterranean currents and wind patterns and the wind-wave cause-effect link.

The Romans introduced many innovations in harbor design. They built walls underwater and constructed solid breakwaters. In some cases wave reflection was used to prevent silting. They used surface-height breakwaters to trip the waves before they reached the main breakwater. They were the first dredgers in the Netherlands to maintain the harbour at Velsen. Silting problems there were solved when the previously sealed solid piers were replaced with new "open"-piled jetties.

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Wikipedia