Natural flood management schemes being used to hold back Debenham’s flood waters
PUBLISHED: 12:12 01 October 2018 | UPDATED: 12:22 01 October 2018
An innovative natural flood management scheme is being trialled around the village of Debenham in mid Suffolk
As its name suggests, the mid Suffolk village of Debenham is located where the River Deben rises and over the centuries it has suffered regular floods - the dates of the bad years: 1912, 1927, 1936, 1944, 1956, 1968 known well by local families. The last serious inundation hit the village in 1993 - rendering roads impassable and damaging over 30 homes. Since that time more houses have been built in low lying areas of the village, putting a considerable number of homeowners at risk of fluvial flooding when the next big deluge comes.
The reason Debenham’s situation is so precarious is down to its location where three tributaries converge - the trio carrying water drained from an extensive catchment area into the narrow river that runs through the village. This complicated geography means traditional methods of flood alleviation have proved too costly to implement in the past - one suggested scheme that never got off the drawing board was a planned large scale £10m concrete reservoir with steel control gates.
But now an innovative project is being trialled that has eschewed the big engineering approach and is instead using natural processes to help manage the risk of flooding.
Slow the flow
Last week, representatives from the main agencies involved in the initiative - East Suffolk Internal Drainage Board, Environment Agency, Essex and Suffolk Rivers Trust and Suffolk County Council - came together with local landowners and other interested parties at Hill House Farm near Aspall outside Debenham to discuss the project and its benefits.
What appeared to be a small lake on the farm was, in fact, a water storage area, recently dug and designed to ‘slow the flow’ by holding water upstream and slowing its progress down towards Debenham in times of peak river flows. The principle is simple - water from one of the tributaries flows through a large pipe into the lake and then flows out of the lake back into the tributary on the other side through a smaller pipe.
This lake/water storage area, which was built last winter and can hold up to 6,700m³ of water, is one of four planned schemes in the area. Two smaller ones have already been dug and a fourth lake, similar in size to that found at Hill House Farm, is due to be finished later this year.
While to the untrained eye, the lake is little much more than a biggish hole in the ground with some water in it - much thought and many calculations have gone into its position and make-up.
“It took me days and days of sums to make sure we had the outflow right,” said Paul Bradford, of Sustainable Water Solutions in Framlingham, who designed the lake, while Pete Roberts, an operations engineer for East Suffolk Internal Drainage Board who oversaw the construction, described the scheme as “low tech and low cost but based on engineering principles”.
Mr Roberts said the total cost of creating the four water storage areas will be around £200,000 and while they won’t be able to prevent the most major floods, he believes together they will be able to hold back enough floodwater to be able to avert the one in 20-year flooding incidents heading Debenham’s way.
While natural flood management schemes of this type cost far less than traditional flood alleviation schemes, another aspect that has excited advocates of this natural approach is the potential additional benefits it could bring beyond flood mitigation.
The lake at Hill House Farm is less than a year old but already reeds have established in some areas and birdlife has dropped in. Farmer-owner Peter Freeman reports having seen Canada geese, grebe and even a lone Kentish plover - taking advantage of the fluctuations in water levels. The larger lakes in the scheme have been engineered to carry some water at all times and it is hoped they will become valuable wildlife habitats as they develop.
Mr Bradford says schemes like that found at Hill House Farm are also intended to improve water quality. As the water stands in the storage area, sediments containing pollutants such as nitrates and phosphates used in fertilisers sink to the bottom, are captured and removed from the water course. The Environment Agency intends to monitor the water at Hill House Farm to chart any changes in quality.
While schemes of this kind have been set up elsewhere in the country, natural flood management projects are “absolutely innovative” for this region, according to Will Akast from the Environment agency, who expects different types of natural flood management schemes to become more mainstream over the coming years (see box).
The water storage areas created around Debenham have only been possible because local landowners and farmers have given up their land to the project without financial compensation.
The Freemans at Hill House Farm say they have got involved because of their love of wildlife and their desire to create a water habitat on their farm.
At the moment there are no subsidies available for farmers who give over land for flood alleviation but it is hoped that this will change, especially in light of the new Agriculture Bill, which promotes payments for landowners who deliver ‘public goods’ such as flood schemes.
This will incentivise farmers to come forward, says Robert Cauldwell, chairman of the Association of Drainage Authorities, who believes the relatively low cost of natural flood management schemes offer people in places like Debenham a viable way of reducing the misery caused by flooding. He said: “While large civil engineering schemes still have their place, there are a lot of small communities who in the past have gone under the radar - this type of scheme is affordable and blends into the landscape.”