Heavy flooding is becoming more severe and more frequent. However, with damaging storm water causing havoc in many exposed communities, we are also seeing more upstream ‘natural solutions’ and fewer downstream hard ‘concrete’ flood defences being used to protect people and property.

This ‘green’ approach, currently supported by circa £15 million of UK Government funding^[1], may be popular with some communities, but is less attractive and problematic to others.

A more basic question is do natural flood management (NFM) methods really work well on their own, or under some circumstances, can they create even greater risks?

Our concern is that natural systems may solve short-term flooding problems but could themselves be washed away by larger downpours unless used in tandem with traditional walls, levees, barriers, and other engineered defences.

What is NFM exactly?

To answer this, I need to explain how NFM works – or perhaps does not work.

Natural flood management (NFM) restores or mimics the natural functions of rivers, floodplains, and wider catchment areas. It does so by holding water back for short periods with foliage, root systems, wet ground, ‘leaky’ barriers, channel diversions, and even beaver dams!

But without proper monitoring and assessments - and understanding the wider effects of, say tree planting on soils, runoff, ecology, and countryside socioeconomics – we cannot know for sure that NFM really does improve community flood resilience.

Tree Leaves and data

One reason is that NFM does often rely on trees to slow heavy rainfall and runoff. But native UK deciduous species are leafless in winter when their canopy cover is most needed.

However, a more important problem is a lack of data! We have little performance information to compare ‘upland’ natural systems with downstream hard concrete flood defences.

Finding the sweet spot

Is there an optimum solution?

Yes, in most cases, if we create (or recreate) ‘natural’ moorland features to delay the first rush of flood water off high ground into rivers and eventually the sea, with the added downstream benefit that any new walls, barrages, and ‘hard’ defences may not then need to be so high or robust.

Best way forward- catchment based approach

However, creating advanced hybrid solutions requires a multi-disciplinary consultancy like Enzgyo (https://enzygo.com/) where ecologists, hydrologists, engineers and other design and planning experts talk to each other and community stakeholders on a daily basis.

Costs, perceptions, and land ownership

Other factors are important too. Cost is one. Attitudes are another.

Many urban communities feel more secure when they can see public money being spent on hard concrete flood defences. However, landownership - and land use - raises further questions.

In the South Pennines uplands, large areas are owned by water utilities. Much of the rest is held privately. Some local authorities own moorland too.

Clearly, finding common ground can be difficult!

Benefits and challenges

We also need to understand key assumptions often made with NFM, plus some of the unintended consequences that good design and planning can prevent.

For example, NFM often involves stopping up moorland drains or ‘grips’ to hinder run-off. This may take off initial rises but seldom reduces peak flow. Once drains are full, runoff continues as before.

Imposed tree cover can also make severe ecological changes to specialised habitats, such as vegetation cover and soils, plus loss of habitats for invertebrates, larger mammals, and birds.

NFM can also hinder traditional moorland management – including legitimate sporting interests like grouse shooting and land management using controlled ‘wet burns’.

By preventing controlled burning, we increase the risk of biomass accumulation (‘leggy’ heather). This in turn creates more dry fuel for wildfires while also shading out other ground vegetation, which paradoxically can lead to increased water runoff from affected ground.

There are also moves to end sheep grazing which has a heavy impact on plant growth. Land management is a crucial key to effective flood control.

Post-Brexit philosophy

This is not the complete story, however.

In addition to its ‘green’ approach to natural flood management (https://www.gov.uk/government/news/natural-flood-management-part-of-the-nations-flood-resilience), the Government released in January 2022 early details of a central funding switch for farmers away from an ‘acreage of agricultural production approach’ under EU rules to a ‘rewards for environmental stewardship’ system.

This will move targets away from pure flood management to a wider basket of environmental benefits linked to adaptation to climate change.

Here once again, more monitoring information will be needed to prove beyond doubt that this well-meaning ‘pastoral’ approach is successful in practice.

Dr Paul Hardwick

paul.hardwick@enzygo.com

https://enzygo.com/

[1] https://www.gov.uk/government/publications/natural-flood-management-programme-initial-findings/using-the-power-of-nature-to-increase-flood-resilience