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ada gazette SPRING 2014 | HEADLINE

ADA produces 10 point fl ood risk plan PETER BIDE (Environment Agency)

With the severe fl ooding of the Somerset Levels and across other parts of the south of England and Wales, a plethora of media att ention has been given to the ways of reducing fl ood risk and the extent of fl ooding when it occurs. In response to the fl ooding, ADA has

publicised a 10 point plan for managing water across the whole of a river’s catchment from source to sea. ADA’s 10 point plan has been adapted from

the plan prepared by the Somerset Drainage Boards Consortium. It focuses on the interconnectedness of water level management across the whole catchment in order to reduce fl ood risk. The diff erent parts

key interests and organisations. It involves the following ten steps: 1. Work with upland farmers and landowners to increase soil infi ltration and store more fl ood water in the upper parts of the catchment.

2. Restore rivers in parts of the catchment that are not artifi cially drained to reduce peak fl ows downstream (and provide other benefi ts for recreation and biodiversity).

Somerset from the air (Environment Agency)

3. Provide fl ood storage areas at critical points in the catchment.

4. Provide assistance to farmers and others to adapt their businesses in areas used for fl ood storage.

of a river catchment and the land uses within it are connected, so that what happens in one area aff ects others. If not positively managed, these interactions can have serious negative impacts; for instance, poor agricultural and river management practice upstream can increase fl ood risk downstream. However, bringing the diff erent activities at the full range of spatial scales across a catchment into a management strategy that makes the most of the possibilities off ered by the interactions can replace the negative impacts with sustainable benefi ts. Managing water at the higher levels of the

catchment through good agricultural and land- management practice retains water to control run- off and reduce peak fl ows, and reduces siltation whilst also providing farmers and land-owners with a more even and reliable water supply. Providing fl ood storage areas further down

the catchment retains water during times of high rainfall to prevent downstream fl ooding whilst also providing a range of habitats to enhance biodiversity and provide the components for nature improvement areas. Surface water should be actively managed

in urban areas. Connecting open space in urban areas provides fl ow paths and water storage to manage fl ows and fl ooding whilst also providing green infrastructure, resilience to climate change and improved urban access. Sustainable drainage systems (SuDS) reduce run-off and store water, managing water at source to lower fl ood risk downstream whilst also providing pleasant open space to enhance the amenity of an area. They can improve water quality and biodiversity and also improve energy effi ciency whilst reducing urban ‘heat island’ eff ects. Where the lower parts of a catchment are

artifi cially drained, channels and ditches must be maintained to transmit excess water through the area into the sea as quickly as possible. Measures are needed to stop high tides pushing water back into the drained area. The plan should be implemented collaboratively by a partnership involving all the

5. Assist farms in areas prone to fl ooding to become resilient to

fl ooding and provide assistance to relocate intensive farming activities out of the fl oodplain with assisted land swaps.

6. Promote sustainable drainage systems (SuDS) and district-wide surface water management in towns to reduce urban run-off .

7. Maximise the conveyance of drainage ditches, channels and rivers in artifi cially drained parts of the catchment and maintain them.

8. Ensure that high tides and tidal surges do not cause back-fl ow and backing up of water in the lower levels of the catchment.

9. Promote fl ood resilience and property level protection in the whole catchment.

10. Promote and assist the relocation of very fl ood- vulnerable households out of the fl oodplain.

Dredging Myths

Flooding in the Somerset Levels has brought questions surrounding the role of dredging to the forefront in the media. Alongside the ADA 10 point plan to managing fl ood risk, ADA has busted some of the myths about dredging in order to inform the public of its true role. This is developed further in our feature on ‘Reducing fl ood risk – dredging and other management strategies’ (page 18) which also provides the views and experiences of IDBs.

 Dredging stops fl ooding No. Nothing stops fl ooding, but we can lower the risk of fl oods by managing the water in a catchment. In low-lying parts of the catchment with artifi cial (pumped) drainage, dredging plays an important part by keeping drainage channels clear so they can transmit the maximum amount of water as quickly as possible through to the pumps.

 Dredging is important to reduce fl ooding Yes, but only in the right circumstances. Dredging is essential in low-lying areas with artifi cial (pumped) drainage to keep drainage channels clear so that large volumes of water can be moved rapidly from areas where the water is accumulating to the pumps. However, in parts of the catchment with natural fl ow, dredging is not generally eff ective in managing fl ood risk except at specifi c points (such as weirs, overfl ow channels and culverts). On open rivers it may cause additional problems by speeding up fl ow in one part of the river so that the water arrives in a peak further down the catchment, causing more fl ooding there.

 Dredging is the only way to lower the risk of fl ooding

No. Dredging is just one of a wide range of measures to reduce fl ood risk, and, as with the other measures, is only eff ective in the right circumstances. Dredging is essential to keep drainage channels clear when large volumes of water need to be moved rapidly across fl at artifi cially drained areas. However, eff ective fl ood risk management uses the appropriate measures for each part of the river catchment; for instance, good agricultural and land- management practice in the upper parts of the catchment to retain water to control run-off and reduce peak fl ows and reduce siltation, fl ood storage areas to hold water at critical points in the catchment, and sustainable drainage systems to reduce run-off from urban areas.

 Dredging damages the environment No, not if appropriate modern dredging methods are used. Man-made drainage channels and modified rivers in areas with artificial (pumped) drainage need to be dredged so they continue to serve their primary purpose of moving water to the pumps. However, careful dredging and bank maintenance can increase their biodiversity and nature conservation potential without reducing their effectiveness as drains (for instance, the water vole is in decline in the UK but continues to thrive in IDB areas).

Witham Fourth IDB dredging Twenty Foot Drain in 2005 (Martin Redding) 5

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