Temmerman & Kirwan (2015) - building land with SLR Flashcards
Coastal lowlands are increasingly exposed to flood risks from sea-level rise and extreme weather events. Where is particularly vulnerable?
Mega- cities like Shanghai, London, New York, and Bangkok that lie in vast river deltas are particularly vulnerable.
Investments in coastal and river engineering, such as the building of dikes, levees, and dams, are often seen as the ultimate solution to combat flood risks and shoreline erosion. However, Tessler et al. reach a rather different conclusion:
Deltas in wealthy countries, which can currently reduce risks by costly engineering solutions, are likely to see the strongest risk increase in the long term, when energy becomes more expensive.
Apart from the socioeconomic constraints highlighted by Tessler et al., there are additional limitations to conventional engineer- ing.
Although it provides effective flood and erosion protection on time scales of years to decades, it disturbs natural delta processes in ways that accelerate local sea-level rise and increase long-term flood risks.
Sand and mud supplied during inundations are trapped in the wetland vegetation, a key natural process that has enabled the vertical building and maintenance of deltas in balance with sea-level rise for thousands of years.
With human settlement, deltaic wetlands are converted into agricultural, urban, and industrial land. In these deltas, flood- protecting structures such as dikes directly fringe the river channels, leaving almost no space for natural wetlands.
When the wetlands are discon- nected from the rivers, the land no longer builds up with sea-level rise. Furthermore, upstream dams often reduce the supply of riverine sediment, slowing down the land- building process in remaining wetlands.
Case studies of human disruption to deltas…
In the Mississippi delta, human disruption to natural delta-building processes are deemed responsible for rapid submergence of the delta plain and subsequent land loss rates as high as 100 km2 per year since 1900.
In the Netherlands, after centuries of soil drainage and land sinking, 9 million people now live below sea level behind costly dikes.
In the Ganges-Brahmaputra delta in Bangladesh and India (with 170 million people, the most populated delta on Earth), land that was embanked in the 1960s now lies 1 to 1.5 m lower than remaining wetlands.
Wetland embankment also triggers extra sea-level rise, why?
Storage area for flood, waters is lost, causing water levels to rise faster in the remaining channels of a delta.
