The delta lands are sinking

When a river flows it picks up all kind of debris from the act of running water over rock, subsoil and soil. Generally rivers deposit this debris, known as sediment, at their moths where they often form large deltas, like the Nile delta or the Delta of the Mississippi. Deltas are made up of many islands formed by the constant deposit of sediment, and they are kept in check by the natural action of the river which washes some of the delta land into the sea.

However, deltas depend for their existence upon the deposit of sediment. People live on deltas and for the people who live on deltas their lives depend on the constant deposit of sediment for the delta to be maintained. If the delta goes so the people have to go. That is what seems to be happening now.

Often, as in the case of the Nile and the Colorado rivers, someone has built a dam upstream, usually for hydro electric power. These dams silt up, holding back the sediment from reaching the delta lands and at the same time making the dams produce less electricity each year. The sediment cannot reach the delta and so the delta washes away or sinks.

This manifests itself in flooding of the delta lands. All told about half a billion people live in deltas and 85% of the major deltas in the world are experiencing more and more flooding.

Other highly populated deltas are sinking for other reasons. The Po delta in Northern Italy has sunk by nearly four metres in the last hundred years because we have extracted the methane gas that lies beneath it for use as an energy fuel. At the mouth of the Po is an extensive delta adjacent to Venice, which is also sinking at the rate of about a quarter of a metre per century.

If you also factor in the effect of sea level rises caused by the expansion of water as it gets warmer and the seasonal greater melting of the polar ice, it is not hard to see why deltas are particularly vulnerable to the effects of climate change and other man made phenomena. The effects of Hurricane Katrina on the Mississippi lowlands and the other serious flooding of the Irrawaddy and Ganges have claimed many thousands of lives. Katrina may or may not have been exacerbated by climate change, but when it struck it did so against a coast that had been weakened by climate change.

When more and more floods come so the half a billion souls who dwell on or near deltas have to remove themselves and this will not only cause hardship to those people but also cause conflict as all mass migrations do.

I am creating a false alarm? I hope so but doubt it. Recently scientists from the University of Colorado have been able to measure from space whether deltas were sinking, and if so by how much. They measured 34 major deltas and found sinking in two thirds of them, including the delta of the Colorado River, which seems to have suffered from loss of sediment due to dams.

When great projects such as the Hoover Dam and the Aswan Dam were conceived it was expected that they would benefit mankind with abundant supplies of electricity and fresh water. They have provided these benefits, but with every benefit comes a burden and in the case of these benefits the burden we shall have to bear is the loss of fertile habituated land in the deltas of major rivers.

3 Responses

  1. Most of what you say is true and such huge power structures like dams etc do not work in the long term, Hoover dam is said to be a third full of sediment already.

    Locally there were 15 mills on only a mile and a half of a local river, which worked for hundreds of years letting the water own to the next and so on, this system is one we should be adopting, not the big ones that cut off the water totally.

    On the part about venice, my mother was born there and she said there used to be many natural water fountains and spring throughout the city, which are now dry, she said that the fresh water used to keep the foundations hydrated and stops the settling we are seeing today.

  2. Interesting reading!

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