Can planned mass tree planting save Leeds from future flooding?

Flooding of the river Aire and its tributaries in late 2015 caused damage put at £500m, following record rainfall across northern England and southern Scotland.

Image: Helena (CC BY-SA 2.0)
Image: Helena (CC BY-SA 2.0)

Eager not to see this repeated, Leeds City Council is spending millions on a "catchment-wide approach" to flood prevention that will include planting "many hundreds of thousands" of new trees upstream of the city.

Much of phase one of the Leeds Flood Alleviation Scheme (LFAS1) to protect the city centre, at a cost of £50m, is already in place. Now, following a Government-funded study in partnership with the Environment Agency and civil engineers, phase two proposals concentrate on upstream measures, combining natural flood management through tree planting and so-called "debris dams" with new infrastructure such as control gates for water retention, and riverbank protection.

The proposed LFAS2 works are eventually likely to cost around £100m, though a bid will shortly be made for initial investment of £3.4m for work including tree planting. A pubic consultation is currently in progress, with an overall business case for the entire scheme being submitted to Government by the end of the year.

Leeds City Council executive member for regeneration, transport and planning councillor Richard Lewis says: "Where possible we want to use natural flood-management measures and let the landscape effectively do the job for us. Planting thousands and thousands of new trees across the region seems simple, but will bring massive benefits not only in terms of flood protection but also to air quality and for wildlife."

Peter Charlesworth, projects director with Mott MacDonald, one of the civil engineering firms that prepared the proposals, tells Horticulture Week: "At these early stages of LFAS2, a commitment has been made to progress advance planting at several sites where it has been possible to identify locations at which additional tree coverage would generate a variety of catchment management benefits." Assessments of further sites, where more extensive tree planting can take place, are ongoing, he adds.

Risk management benefits

As to determining the flood-prevention value of such work, he says: "The LFAS2 project team is engaged in investigations to evaluate the flood-risk management benefits of a variety of catchment management measures," adding: "The underlying evidence base for quantification of the flood-risk management benefits of tree planting and other measures is evolving."

He points out that the planting proposals tie in with other tree planting initiatives in the area already underway, under the emerging Leeds City Region Green Infrastructure Strategy, Northern Forest & White Rose Forest, "which generate benefit from investment beyond flood-risk management alone".

The Woodland Trust’s lead on its Street Trees project, Joseph Coles, welcomes the city’s plans. "It is this sort of forward-thinking initiative that led us to choose Leeds as one of the pilot regions for our Street Trees project, which aims to recognise tree-friendly cities who remain determined to increase planting and canopy cover," he explains. He describes the trust’s project as "part of a holistic approach to environmental improvements in urban areas and beyond".

Coles says of the River Aire plans: "By increasing planting and habitat creation along its catchment, the benefits it brings to people and wildlife can only be improved. Tributaries of the Aire are home to some rare native species and as these pass through some of the more urban areas of Leeds so creating additional habitat protected from development can vastly increase their chances of survival."

More widely, he says: "This model should be considered by other local authorities, and indeed there is a concerted effort by others for a joined-up approach to whole catchment flood alleviation, of which tree planting is a major contributor."

Planting commitment

The Government has already committed to planting 11 million more trees by 2020, though this now thought unlikely to be met. Defra secretary Michael Gove spoke in July of trees as "living evidence of our investment for future generations, a carbon sink, a way to manage flood risk and a habitat for precious species".

Coles says: "Government investment in schemes such as in Leeds would be welcomed by people and local authorities affected, and would lead to massive reductions in the clean-up costs following intense weather events."

He adds: "We’d always recommend native and local provenance trees, especially in upland and more rural environments. In the more urban places, the council will undoubtedly consider a variety of species, with climate change resilience, tolerance of urban environments and effective tree establishment being among the considerations."

As to whether such woodlands could be harvested for timber, he says: "While this might provide income for long-term maintenance, there needs to be a strong market for homegrown timber and infrastructure in place to make it viable."

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