Floods & tides also threaten London

Posted on September 13, 2017


The destructive winds and catastrophic floods that struck Texas and Louisiana, followed by the devastation wreaked on a large swathe of the Caribbean and Florida should be a wake-up call, especially to every coastal city on earth. Coupled with the the floods and landslides in Nepal, Bangladesh and parts of northern India, along with the landslide devastation in Sierra Leone, it should now be obvious that the world has entered into a period of often dangerous climatic instability.

This is a consequence of naturally occurring warming exacerbated by the massive production by modern industry of greenhouse gases. To maintain, as do US President Donald Trump and Britain’s former economics minister, Nigel Lawson, that climate change does not exist and that there is no human-driven contribution to global warming, flies in the face of facts that are now readily available.

There is scientific consensus that the planet has been warming since the last Ice Age, But, since the advent of the manic, fossil-fuelled drive for ever greater economic growth, the rate has increased exponentially.

The media focus — when there is any focus at all — tends to be on gradually melting glaciers and polar ice caps. But this is not the main issue. Nor, immediately, is the slow rise in sea levels that is measured in millimetres.

The greatest danger now comes from a general warming of the oceans, and the consequent effect on climate. Warmer seas mean greater precipitation of ocean water, more stormy weather, and often massive downpours of rain on inland areas.

But rivers anywhere, such as the Jukskei in Johannesburg that regularly washes away shacks built on its banks also pose threats as urbanisation encroaches on river banks and on what were once flood plains and marshes. Coupled with increasingly turbulent seas, this makes for a potentially lethal mix.

Yet the sea alone is enough to challenge and seriously damage encroaching human habitation. And South Africa is not immune, although the scale of potential devastation seems relatively minimal: the loss, perhaps of the coastal railway line beyond Muizenberg and of the often sand clogged and tide washed Baden Powell Drive, both in the Western Cape; along with, perhaps, some heavy erosion of beaches on the KZN coast, endangering shoreline properties.

The densely populated and low-lying areas of Lagos in Nigeria are a different matter. As, indeed is Alexandria on the Nile delta in Egypt. The very real dangers to both of these have been highlighted in the past by University of Cape Town oceanographer Geoff Brundrit. Especially in the case of Lagos, the possibility of great destruction and massive loss of life exists.

But one major low-lying city on a tidal river seems largely to have escaped much scrutiny in terms of the latest fears about flooding: London. Because, ever since 1983, this very low lying city on the banks of the river Thames has had a massive, mechanical steel barrier comprising six 3 700-ton gates, maintained by the UK Environment Agency, that is raised to stop potential flooding.

The official line is that this £1.6billion (R27.2 billion) construction near Greenwich will be adequate until 2030 or even 2070. But there is growing evidence that this estimate is not only too optimistic, it may be plainly wrong, given the changes in climate and rainfall figures.

Most of the reference by the Environment Agency to the continued security of the barrier is to rising sea levels. Yet a number of oceanographers and other specialists have warned that the real danger is not so much rising sea levels as the greater storms precipitated by climate change, coupled with torrential downpours of rain in inland areas.

Brundrit has pointed out that the Thames barrier, which, in 1972, was expected to be raised twice to three times a year, now averages more than more than twice that number as floods have threatened. In one ten-day period, three years ago, it had to be raised 20 times in ten days.

The barrier has also had to be raised to stop the North Sea tide from adding to rising river levels caused by heavy rainfall in the Thames valley. The water is dammed up and then released into the sea at low tide, something not considered when the barrier was built.

This has led several specialists, including Dr Richard Bloore who was part of the project management team that built the barrier, to warn, as far back as 2013, that the barrier was coming to the end of its useful life. A combination of heavy inland rainfall and a Spring tide in the North Sea could swamp the steel gates and lift the tidal rise more than a metre above the present 7 metres/23ft.

If the Thames burst its banks, the results could be devastating since many parts of this sprawling city are between 3metres to 7metres above sea level, with much transport and electrical infrastructure below ground. The city long ago encroached on the marshes and mud flats of a river that is really an extension of the strongly tidal sea. At high tides, water now laps near the tops of the embankments on the north and south sides in the centre of the city.

It was, in fact the floods of 1928 and, especially 1953, that led to the decision to build the barrier. Then it was mainly poorer citizens who lived in the low-lying areas around what were working docks and settlements along a quite polluted waterway that were the main sufferers. Today fish live in the Thames and the glittering apartments of the wealthy line its banks, so the cost, in material terms, could be massive should the water surge above the 7metre mark.

And while the sea level is only rising by millimetres, London, built on clay, is also very slowly sinking by minute amounts. This merely adds another concern to what should be a serious worry for an already economically weakened UK.

Posted in: Environment