Thursday, 4 July 2013

It all comes flooding out.

It BBC and Government have put flood defence back in the news, as far as I can see this is completely the wrong agenda. Floods are inevitable all you can do is move it to a different place on the river.
Over centuries rivers have been forced into smaller and smaller courses by the building of embankments and the reclamation of land. Rivers like the Thames are half the width that they used to be. The Mersey used to start at the bottom of Water Street in Liverpool the Goree and the Pier head are all built on reclaimed land. All of the docks, bar Herculaneum, were built out into the river. This has very little effect on Liverpool due to it essentially being the estuary but in other places the narrowing of the course constrains the river and in order for the same volume of whether to pass it must travel faster. In other places it forces the river to be deeper.
While Global Warming may increase the frequency of heavy rain it is not the only or even primary cause of increased flooding. A river's water comes from its catchment area and depending on the topology and geology of that taking time to go from being rain, or melt water,  to river water or at least it used to. In large areas now the land is either waterproofed with tarmac or fitted with drainage systems, which speed the flow of the water to streams and other tributaries reducing the time over which the water is dumped into the river. This causes flooding. In the past only rivers with catchments of particular geologies suffered from flash flooding where with hours the rain that fell over a large area moved down the stream, now it is far more common.
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The use of permeable surfaces, where ever possible, would allow a large portion of rain to be temporally stored in the soil, where it fell then slowly being released into rivers. If all amendable surfaces were made of "grasscrete", then the effects of flash flooding could be reduced and additional greenery be provided. 
Rivers have influenced greater areas than just between their banks, each river has a flood plain of some size, that is the area which when it gets too full it overflows into. These are so common an occurrence that the nature of the land in these flood plains is changed by the floods. The years of sedimentary deposits flatten out the land and produce rich fertile soils. Entire civilizations have developed on flood plains, Egypt is the most obvious but it also applies to the Indus cultures of the Indian sub content and Amazonia.
These civilisations took advantage of the river to grow, they worked with the floods, failure of the floods was a serious matter that could result in famine and starvation. Today, in our country our floods result in mass inconvenience, they actually kill very few people, but news crews are dispatched and cover in great detail the rise and fall of these natural events as if they were unexpected. Houses are flooded and cars are washed downstream.
There are exceptions like Boscastle where the events happened so quickly deaths are almost inevitable but in most cases a flood of the Seven or the Trent is an event which has hours or days of warning. It should not be a cause for panic but the trigger for a series of well understood practises which minimise the disruption.
If you build on a flood plain, then you build on stilts or have a ground floor garage. It cannot be beyond the wit of man to produce an electrical system which can survive a flood at the very least putting the vulnerable stuff up near the ceiling should work. Water proof plaster is available and used by people in wet rooms it's use in the living room is hardly a great handicap. A quick search on the Internet for "flood proof home" give lots of advice and while it make take some getting used to have in the washing machine on stilts is a minor inconvenience compared to not having one. Fitting door guards and snorkel bricks, with rugs and carpets that can be easily moved to the next floor. Having a small portable generator that can be used to power the upper floor and an electrical system design allow this when the ground floor is flooded.

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