Keeping Derby dry

Like many other cities, Derby has a river running through its centre.  Rivers can supply water for drinking and washing, power for industry and sometimes also transport – though the Derwent is a little small for this last.

But alongside these attractions, rivers can also be a liability; after heavy rain they can flood.  Indeed, as well as the River Derwent, fed from the hills of Derbyshire, Derby also has several significant streams which can also cause localised flooding, such as the Markeaton Brook.

The 5 arches bridge, carrying the main railway over the river, raises the level of the river upstream, adding to the risk of Derby flooding.

The 5 arches bridge, carrying the main railway over the river, raises the level of the river upstream, adding to the risk of Derby flooding.

Although Derby has recently been spared widespread flooding, the risk is growing.  There are many factors, from changing land uses upstream to possible obstructions downstream – but one of the most significant and challenging is climate change.

One of the affects of increasing CO2 levels in the atmosphere is  more extreme weather events.  The likelihood of heavy rain, maybe up on the Derbyshire hills, leading to flooding in Derby is increasing.

The impact of a serious flood can be devastating at many levels; homelessness, mess to clear up, loss of belongings, damage to property, the cost of rebuilding, the inability to get – or very expensive – insurance, and so on.

Is there anything that can be done?

There are already some flood defences in Derby, such as walls built near the top of the river bank, but will these work?  And for how long?

Ground samples from about 1m down (front) showing land built up for the railway on top of housing going down to natural gravels.

For several years the Environment Agency has been looking at cities most at risk of flooding, and it has been considering what could be done to help – and whether this would be cost-effective.

 Derby is one of its priority cities, and the Our City Our River project has been set up to explore the best options to avoid Derby being flooded in the future.  Various meetings have been held to talk with local people about the risks of flooding and what could be done to reduce these risks. 

Lucy Care at a borehole test site in Little Chester.

Lucy Care at a borehole test site in Little Chester.

Further work is being done to identify what solutions might work best – and how much these might cost.  Current estimates suggest that over the next 30 years it might cost around £80 million to reduce the risk of flooding to less that 1 in 100 year levels.

Actions to be taken are likely to include making more space for water to spread out – so that it doesn’t get so deep – and stopping it soaking through under existing (or new) flood defences.  The gravels on which some of Derby is built are very permeable.

The changes won’t all happen at once.  Although the likelihood of heavy rain rises as CO2 levels rise, action to reduce the impact of the extra water can be taken to keep the actual risk of flooding much the same over time.

 

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