Delta Life 8

18 1 2 3 Worldwide, more than forty billion tons of sand and gravel are extracted annually, about twice the amount of sediment delivered by all the rivers in the world. Increasingly, coastal erosion is caused by human activities. River dams stop the passage of sediment to the sea. Sediment disappears into deep fairways. Built structures in the water disrupt natural currents. Illegal sand extraction and climate change exacerbate the problem. The power of the waves and the currents in the sea constantly eat away at the coastline. The same water also brings newmaterial. Coastal erosion begins when not enough newmaterial arrives. Changes in the coastline have always been with us. Coasts grow in some places, and erode in others. Coastal erosion becomes a problem only when the coast crumbles where large numbers of people live and work. What next? BY KARIN STONE IMAGE ISTOCK COASTAL RESIDENTS UNDER PRESSURE: MORE CITY, LESS LAND