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Much of your reporting on the Derna flood disaster (Libyans demand investigation as fury grows over catastrophic flood toll, September 14) has focused on the condition of the dams and the political situation, as well as than on the extreme weather event, but there is another factor that makes the city very vulnerable. It appears to be built on an alluvial fan – a cone-shaped landscape feature, formed over millennia by the deposition of river sediments. These features form where steep rivers emerge from the mountain highlands, spread out, and divide into a series of distributary channels along the fan (like a delta).

In many cases around the world, such as at Derna, water flow was arranged in a single channel cut into one flank of the cone and construction was permitted up to its margins. In an extreme event, as occurred here, the enormous flow of water returned to its natural channels, overflowing the restricted channel and flowing in multiple pathways along the fan on which most of the city is built.

Such places are particularly vulnerable to the effects of extreme flows and demonstrate the dangers of attempting to control nature through large-scale canal diversion and filling. It is essential, particularly in the context of climate change, that natural environments and situations are recognized and that we work more with nature to sustainably manage floods and rivers.
Professor Janet Hooke
University of Liverpool

On November 2, 1925, the Eigiau Dam in North Wales broke, releasing 70 million tonnes of water into the valley. Ten adults and six children were killed. Since then, no deaths have been caused by a dam failure in the UK. There are over 2,000 tanks in the UK holding over 25,000 cubic meters of water. It is shocking to see how many buildings are now at risk of flooding from dam failure in flood risk maps published on the government website.

Building permits are still regularly granted for new developments in flood plains and in the shadow areas of dam breaches. Surely this should be illegal due to the increasing number of lives destroyed for those living in flooded homes. The Libyan dam failure demonstrated how catastrophic the effects of a major dam failure can be. It may only be a matter of time before Britain’s dams are also put under strain by the increasingly extreme weather events we are experiencing here.
Susan Roaf

The flooding in Derna is undoubtedly the result of the climate crisis and may well have been avoided by competent governance (The Guardian, Libya flood view: Humans, not just nature, caused this disaster, September 13). But few people know that during Muammar Gaddafi’s tenure there was a strategic plan to develop the entire vast Libyan coastline, from Tripoli to the Egyptian border, for tourism, creating new cities, improving conservation and modernizing thousands of kilometers of infrastructure.

A coastal pipeline was under construction before the war to bring fossil water from the Sahara to irrigate what was once the breadbasket of the Roman Empire. As part of my work as a landscape architect, I designed four national parks, including Al Guarsha in Benghazi.

Many new hospitals and universities were being built, but all came to a screeching halt at the start of the “green revolution” which was crushed by the regime, before Gaddafi was in turn deservedly defeated in the conflict that followed. . After David Cameron’s bold promises of democracy and freedom in Benghazi at the end of the war, what role did Britain play in rebuilding post-conflict Libya?
David O’Brien
Director, D.obla Landscape Architects

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