Slowing down

Taken mainly from the final report for the ‘Slowing the Flow’ Project

The ‘Slowing the flow’ project is now completed, ahead of approaching winter. The purpose of the project has been to reduce the risk and severity of flooding in Pickering and nearby Sinnington.

The approach has been to slow the flow of water from off the moors into Pickering Beck and the River Severn and subsequently down into the settlements below.

The last element has been the creation of a flood storage area at Newbridge, upstream of Pickering – a site to hold up, and so slow down, extreme flows of water. It can hold up to 120,000 m3.

The ‘Slowing the Flow’ project was one of a number of Defra pilot projects looking into reducing flood risk and impacts. The idea was to make the best use of natural processes by adapting land use and land management to slow down and delay the passage of water.

Phase 1 of the project concentrated on building up a working partnership including with the local community. The National Park Authority were heavily involved in Phase 1 of the project as a major landowner in the area. The National Park Authority owns Levisham Estate upstream of Pickering and a number of tributaries into Pickering Beck arise on the Estate’s moorland.

View of Hole of Horcum (part of Levisham Estate) - copyright Mike Kipling, NYMNPA

The land management work undertaken in the two sub-catchments included establishing no burn buffers along moorland watercourses to protect soils and retain vegetation, impeding moorland drains using heather bales to lessen erosion, constructing ‘woody debris dams’ which slow but don’t halt watercourse flow, creating riparian buffer zones in forestry, and large scale tree planting and long term woodland creation because trees prevent sediment runoff and hold and use more water than other habitats. Two timber bunds were also constructed in the River Severn catchment. 

Large woody debris dam during flood - from Forest Research: appendices to Phase 2 Final Report, May 2015

Large woody debris dam secured by angled posts and wire on Pickering Beck - from Forest Research: appendices to Phase 2 Final Report, May 2015Face of upstream timber bund within Forestry - from Forest Research: appendices to Phase 2 Final Report, May 2015Small woody debris dame - Horcum, Levisham Estate - NYMNPA

 

 

Heather bale 'check' dams within moorland drain - from Forest Research: appendices to Phase 2 Final Report, May 2015

Drainage channel - Fen Moor, Levisham Estate - NYMNPA

Slowing the Flow in action - Levisham Estate - NYMNPA

 

 

 

Slowing the Flow tree planting - Levisham Estate - NYMNPA

Phase 1 (2009 – 2011) led to Phase 2 (2011 – 2015) which allowed for the implementation of the outstanding land management interventions planned. One of the lessons learned was that five to six years is a more effective time scale for delivering a demonstration project, especially one that includes persuading landowners to change land use. Another lesson is that the measures undertaken have to be at an effective scale – the bigger the contribution to flood protection required, the larger and/or more extensive the measures need to be at the catchment level to make a difference.  The use of smaller, more diffuse, storage features can collectively contribute a sizeable flood storage volume, depending on their design and management – however catchment level planning/modelling is needed to guide and achieve the optimum placement and combination.

The ‘Slowing the Flow’ project was led by Forest Research, and the partnership that made it happen included the Forestry Commission, the Environment Agency, Natural England, North Yorkshire County Council, Ryedale District Council, the North Yorkshire Moors Railway, Durham University, Pickering Town Council and Sinnington Parish Council and the local community including vital landowners, and us. The project was possible only because of this joined up and inclusive approach to flood, water and land use management. Another lesson from the project is that efforts to reduce flood risk via land management interventions can be accidentally counteracted by other activities in the same catchment.

Although the main purpose of the project was to lessen the risk of flooding in Pickering, and also the village of Sinnington, the methods used will provide added benefits to biodiversity and the wider ecosystems. The piloting of the practical demonstrative measures have allowed the sharing of good practice, knowledge and skill development (e.g. NYMNP Apprentices).

Some issues…

Concerns over the stability of ‘woody debris dams’ and the potential for debris to wash out and damage downstream structures need to  allayed by the construction methods that use slot trenches and bracing logs to attach the structures to the banksides.

Having a National Park – a designated landscape – in the north of the sub-catchments had implications for the siting and design of land management interventions. For instance from a National Park point of view there was a limit on how much tree planting could be/should be accommodated on the Levisham Estate because of the ecological value of the existing moorland habitats which are designated as a Site of Special Scientific Interest and in some places also a Special Protection Area/Special Area of Conservation.

Persuading people to create woodland can be difficult. The selection of Pickering Beck as a demonstration sub-catchment was partly because of the relatively high level of public land ownership e.g. National Park, Forestry Commission. In the future achieving the necessary sizeable level of change on privately owned land is likely to require greater financial incentives. The new, integrated, Countryside Stewardship scheme should help by providing grant for planting that provides benefits, including reducing flood risk and diffuse pollution.

Conclusions…

Land management measures can make a significant contribution to downstream flood alleviation. They vary in type, size, scale of operation and mode of action but are most effective in combination as part of a whole catchment approach to managing flood risk. More modelling and experience of actual flood peaks is required to better understand the cumulative effect of the measures. In view of the level of commitment and investment required, resources are best focused on small to medium sized catchments that can be expected to deliver large-scale changes in land use and/or management.

It is not suggested that the ‘Slowing the Flow’ project will prevent all flooding in the two sub-catchments, but it is anticipated that there will be less flooding. It has been suggested that the previous 25% chance of flooding in any given year in Pickering, has now been reduced to a 4% chance or less…

2 thoughts on “Slowing down

  1. The force of flood water is being underestimated in this project.
    Floods will have the ability to scour new channels around the blockages in a single flood event.
    Untreated timber used in the dams will have a lifespan of ten years at best before the structures start to fail. Woody debris will be washed downstream and cause blockages which will exacerbate damage in locations which might not normally be at risk

    The flood storage area at Newbridge is a good option and will undoubtedly help especially in sudden but relatively brief flash flows such as thunderstorms.

  2. Pingback: Loving Levisham Estate: a personal view point | The official blog for the North York Moors National Park

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