Case Study

Natural Flood Management Pilot, UK

Sector: Transport
Highlights: Biodiversity, ecological uplift, road safety, collaboration
Project owner: National Highways
Project start:
August 2018 – March 2023
Location: North-West England
Community impacted: Urban, Rural
Hazards mitigated: Flooding
Number of people made more : ​ +300,000*
Case study provided by:  National Highways through support from the IAM Climate Emergency Group

*Estimation based on 65% commuter journeys (single car occupancy) and 35% leisure (2 people occupancy)

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Areas of the UK Road network are highly susceptible to closure due to surface water flooding. The Natural Flood Management Pilot supported catchment landowners to implement natural attenuation measures to reduce flood risk at the source. The pilot has demonstrated how a national infrastructure provider can collaborate to deliver nature-based solutions and has delivered multiple benefits for the landowners involved in the scheme who have forged new connections within the community.

About the Project

Surface water flooding on UK roads and the subsequent travel disruption affects communities in and around these locations and has significant safety and cost implications. National Highways committed £1.1m to investigate the use of Natural Flood Management (NFM) measures to increase resilience to flooding on susceptible roads from runoff generated up-catchment.

Natural Flood Management (NFM)

The pilot tested a methodology for National Highways to engage and support owners of land ‘off-network’ (i.e. third-party land) to implement NFM measures in a way that generates tangible benefits and is replicable across the network. The project had a number of key objectives, namely: to evaluate the ability of natural measures to increase flooding resilience and reduce the need for traditional hard engineering solutions to flooding hotspots on the road network; to demonstrate a framework to deliver off-network catchment-scale projects using community partners as a delivery mechanism; to trial a novel bidding technique to drive value for money in implementation; to maximise environmental outputs through co-benefits of nature-based solutions; and to evaluate the potential to scale-up across the network.

The pilot locations were selected within the Little Don and the Irwell river catchments in north-west England, the catchments bordering the A616, M62 and M66 roads. All of these had incurred lane closures due to localised surface water flooding on multiple occasions. Partnerships were therefore initiated between National Highways (supported by NFM Specialists AtkinsRealis), catchment landowners and community delivery partners, The Mersey and Don Rivers Trusts.

National Highways provided funding, project management, legal services, and contract development with technical support and NFM expertise from AtkinsRealis. National Highways also provided local knowledge on the location and severity of flooding at flood hotspots on the network in the focus areas. The Don and Mersey Rivers Trusts were National Highways’ Catchment Partners. As an established local presence trusted by landholders in the catchment, and knowledgeable about implementation of NFM, the Trusts acted as a bridge and intermediary between National Highways and local landholders. Landholders provided the land on which measures were implemented in a five-year agreement with National Highways. They implemented the measures and will continue to maintain them until 2028. Collaboration and partnerships between all stakeholders involved will be key to the long-term sustainability of this approach.

The pilot was delivered in four phases:

  1. Scoping (2018-2020) – An England-wide study was done to identify 100 catchments with geography suited to NFM and records of known problematic flood risk to the road network.
  2. Opportunity (2020-2021) – A detailed investigation took place to locate catchments in which the flood risk needs of National Highways aligned with those of community delivery partners and to undertake an analysis of the opportunities to address those needs using NFM.
  3. Implementation (2021-2022) – The development of the partnership with The Rivers Trust at two pilot locations and an agreement on the financial and legal structure between National Highways, The Rivers Trust and landowners was established. Work was undertaken with the Trusts and landowners to deliver measures on the ground and then monitor and evaluate success. Auctions in which landowners bid for funding took place in June and November and work commenced in March 2022.
  4. Evaluation (2022-2023) – NFM measures were selected based on cost-effectiveness and ease of maintenance and implementation for landowners. Landowners were able to submit bids for funding via an online reverse auction based on ‘live’ environmental modelling data, including estimates of storage volumes. This is thought to be the first time such an interactive and dynamic approach has been used to bid for NFM measures in the UK.

Achieved Outcomes

Social

Multiple communities surround the localities and will benefit from improved connectivity, reliable journey times, and improved safety. The A616 connects Sheffield, Huddersfield and Manchester, while the M66 and M62 connect Greater Manchester to key commuter towns and cities in Lancashire and Yorkshire. The project reduces the need for traffic management and provides reliable commuter routes.

Environmental

The project has reinstated natural water attenuation and storage measures into river catchment slopes that, at some point in history, had the tree cover removed and land converted for agriculture or pasture. Implemented measures have generated a combined estimated storage potential of 5,800 m³ of water. By installing measures such as storage ponds, cross slope hedges, and tree planting using native species, co-benefits such as habitat creation are generated. Soil aeration and planting herbal ley help to improve soil quality and prevent soil erosion. Improved ecosystem services have also been generated through carbon sequestration and water quality improvement, increasing resilience to climate change.

Natural systems have been reinstated to some extent by the measures implemented in the catchment. Biodiversity resilience within the area will be bolstered by new hedgerows and tree planting, which will provide habitat and food sources. Attenuation ponds and slowed streams will enhance their ability to support aquatic species. The pilot has made a vital contribution to understanding the viability of the NFM measures. It has demonstrated the added value to biodiversity, carbon, as well as water and air quality generated by measures primarily implemented to increase the resilience of roads to flooding.

Economic

The pilot has delivered 129 individual NFM measures across 20 landholdings, with a combined estimated storage potential of 5,800 m³ of flood water. Understanding the relative value of these multiple benefits has optimised the design of NFM moving forward. The combined value of the interventions has been estimated at £643,000 over 25 years. It was noted that the cost-effectiveness of delivering NFM versus a traditional small-scale flood attenuation scheme compared favourably, with lower whole-life costs per cubic metre of storage.

The assessment also demonstrates a feasible approach to better target locations for delivery to maximise total benefits, including those areas with the greatest consequences for flooding. This model is applicable to other linear networks or distributed national estates.


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