Factors Increasing Flood Risk
- Local factors increase flood risk on some low-lying and estuarine coasts due to:
- Height of land
- Degree of subsidence
- Vegetation removal
- Global sea level rise further increases risk
- Densely populated coastal areas also increase the number of people at risk
- Low-lying coastal areas are often densely populated due to:
- Attractive scenery and beaches
- Deltas are fertile and ideal for agriculture
- Suitable for ports and trade
- Globally, almost 300 million people live in coastal areas below 2m
- Of the 10 world's largest cities, 8 are in coastal areas
- Countries and regions which are particularly low-lying include:
- Bangladesh - over 10% of the land is 1m or less above sea level
- Maldives - has an average height of 2m above sea level with highest point being 2.4m
- Netherlands - 27% of the country is below sea level and protected by sea defences
Height of land
- Low lying areas are more vulnerable to rising sea levels and storm surges
- Storm surges and spring tides leads to water flooding areas of the back-shore and beyond
Degree of subsidence
- Coastal areas are vulnerable to subsidence particularly deltas and land reclaimed from the sea
- Clearing land for agriculture and ground water abstraction, increases the risk of subsidence
- Building of settlements, along with the weight of the buildings, increases the risk of subsidence
- When subsidence occurs, the land is then lower and more vulnerable to coastal flooding
Vegetation removal
- The removal of vegetation, including salt marshes and mangroves, increases coastal flood risk
- It is estimated that 50% of salt marshes and 35% of mangroves have been lost since the 1950s due to:
- Reclamation for development - housing and transport
- Coastal management such as sea walls
- Tourism, to create beaches with open views to the sea
- Shrimp farming
- Where vegetation exists, it significantly impacts wave height, which reduces the risk of flooding:
- In the UK, salt marshes are estimated to reduce wave height by up to 80%
- 100m of mangroves is estimated to reduce wave height by between 13-66%
- The vegetation:
- Traps sediment, which helps to increase the land height
- Reduces the impact of waves and erosion because, it absorbs the wave energy