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Floodgates opening on ancient woods?

Trees and woods can play a vital role in reducing flood risk and we work hard to ensure their potential is fully realised. But suggestions to deliberately submerge ancient woods as flood water storage areas are not something we want to see.

Floods can devastate homes and communities. The clean-up (where clean-up is possible) can take months, costs can spiral and it can be hard to cope with often significant losses and the emotional aftershock of such a disaster. Using woods as part of a natural resource management tool, for example to slow the flow of flood water can be very effective as part of a wider, sustainable land management strategy. But storing flood water will transform a habitat irreparably.

Ancient woods - formed of complex soil systems established over hundreds of years, and home to rare and vulnerable wildlife - are not acceptable natural options for flood storage.

Yet in Sheffield, three ancient woods have been put forward as flood storage areas. We are urging local people to respond to the Upper Don and Sheaf Flood Protection Consultation before it closes on 31 October. We will be making a formal submission too.

We will share this in a follow up blog next week.

Waterlogged

The prospect of using any ancient wood to store flood water is very concerning. No woodland will cope with long periods of submersion, even wet woods with their distinctive adaptations. Storing water in any woodland habitat for a significant period of time will kill off most of what makes it special.

Ancient woods should only be considered in a flood management strategy where there is a history of inundation and the site shows the characteristic flora of wet woodland. If the site is a wet woodland (adapted to cope with regular inundation) that is now disconnected from its floodplain, including this in a strategy could be a positive move. Wet woodland is a special conservation category in its own right because of its special ecological importance.

Find out more about wet woodland from the Forestry Commission's 2003 Practical Guide on Managing Wet Woodlands (PDF, 1MB)

If the ancient woodland is on steep slopes with steep-sided stream gulleys, then using large woody material in strategic locations to form “leaky” dams could significantly slow the water flow and wouldn’t necessarily be damaging. A ‘dry’ ancient woodland, with no previous history of inundation, is not an appropriate option.

From a conservation point of view, short term flooding of woods is unlikely to negatively affect the trees and shrubs directly but may cause nutrient enrichment of soils or pollution (from sediment or pollutants in the flood waters), thus impacting the ground flora and possibly killing invertebrates or other animals like dormice overwintering in the ground. But longer term or more frequent flooding will start to kill the trees.

It’s crucial to seek independent advice before considering any sites as storage. An assessment is the most important thing a Lead Local Flood Authority should do. It could be that a portion of the sites put forward are used to changes in water level, for example being so close to the river. But without a survey it is very difficult to know the wood’s ecology, and therefore what the impacts could be. The risks to these unique, and irreplaceable, habitats are too great.

Enough is enough

We can’t let precious habitats like these go under without a fight.

If you live in and around Sheffield please urge the Council to remove the ancient woods put forward as water storage sites from its draft flood management strategy. Respond to the consultation before 31 October.

Check your ancient woods are not at risk. The Lead Local Flood Authority is responsible for developing and delivering a Flood Risk Management Strategy in your area and should consult residents. Search online or contact your local authority for information. And please let us know if any ancient woods are included as an option for water storage.