Geography
How Land Reclamation Alters Coastal Sediment Budgets and Habitats
Quick fact
In the Yellow Sea, more than 70% of tidal flats have disappeared since the 1950s, much of it due to land reclamation, leading to dramatic losses of shorebird stopover habitats.
Why this is interesting
You've seen vast new city districts rise from the sea—but have you ever wondered what happens to the beach next door? Land reclamation doesn't just create land; it quietly steals sand from elsewhere along the coast.
Read the full explanation
Understanding How Land Reclamation Alters Coastal Sediment Budgets and Habitats
Think of a coastal sediment budget like a bank account: sediment (sand, silt, gravel) is deposited from rivers, eroded from cliffs, and moved along the shore by waves and currents. Reclamation acts like a sudden withdrawal—it removes sediment from the system by covering it with new land or by blocking its movement. When you construct a seawall or fill in a bay, you interrupt the natural flow of sediment that would normally nourish beaches and wetlands downstream. The result is that those areas begin to erode faster than they can replenish, a condition called 'sediment starvation.' Meanwhile, the construction itself often requires dredging, which smothers nearby habitats with excess silt. So reclamation both takes away sediment and adds it in the wrong place, throwing the coastal ecosystem off balance.
A deeper explanation
The mechanism is rooted in the sediment budget equation: the amount of sediment entering a coastal cell minus the amount leaving it equals net change. Water moving along the coast (longshore drift) constantly transports sediment, and natural features like mangroves and tidal flats trap sediment, building up their own elevation. When land is reclaimed, the new structures (such as seawalls, breakwaters, or filled land) block sediment transport, preventing it from reaching downstream areas. This reduces sediment input to those areas, causing erosion and loss of valuable habitat. Additionally, the reclaimed land itself is often built on former intertidal zones—the most productive habitats—so their biomass and ecological functions are lost outright. The loss of these habitats not only reduces biodiversity but also removes natural storm buffering and nursery grounds for fish, impacting fisheries and coastal protection. This explains why reclamation can lead to a downward spiral of ecological and physical degradation, and why careful sediment management is essential to mitigate impacts.