Floodplain Reconnection (Stage 0) webinar

Today I attended the Floodplain Reconnection (Stage 0) GIS data release webinar hosted by the Dorset Catchment Partnerships. The webinar introduced the Environment Agency's Floodplain Reconnection (Stage Zero) Opportunity map GIS layers. Natural Flood Management lead Aly Maxwell and consultant hydrogeomorphologist Peter Stone explained how the layers have been created and used in project planning for multiple benefits.

Fiona Bowles, Dorset Catchment Partnership Chair introduced the session, outlining what Stage 0 is and how it has recently developed. Large-scale floodplain reconnection has been carried out in Oregon on the West Coast of the USA, and although it is harder to achieve in the UK, we are looking at ways to apply this on smaller scales in our constrained rivers.

Aly Maxwell (Environment Agency NFM Adviser) also mentioned how Stage 0 is a whole catchment approach which aims to retore natural processes. It offers multiple benefits including water quality and biodiveristy improvements, by considering how water flows through the catchment, how it is slowed and how it is stored. Aly mentioned the range of terminology which can be used to describe this approach – floodplain restoration, floodplain reconnection, Stage 0, and Valley Floor reset. Achieving multiple benefits is a key part of how Environment Agency will be driving projects in the future.

Dr Peter Stone then gave a presentation on the Wessex Stage Zero Opportunity Mapping project, and considerations for a Stage 0 approach to restoration.

This approach considers water flow, morphology and form, biological elements and creation of habitat. The technique aims to raise the water table and reconnect base flows. Peter mentioned how Stage 0 terminology comes from pioneering work of Cluer & Thorne (2013). Stage 0 is a river form, not a technique. The techniques installed are trying to achieve a full floodplain reconnection, with wandering channel morphology and connected wet woodlands. We need to make the distinction between full floodplain reconnection and creating floodplain storage. Similarly, we need to make the distinction between enhancement or re-attachment of existing habitat and starting again from scratch or recreating new habitats.

Peter talked through the elements that make up a Stage 0 river form. These things need to be given a relative importance for the opportunity mapping approach.

• Physical characteristics – controls on the river and landscape morphology (geology, landform, fluvial, land use, water slope, stream power, sediment supply)
• Anthropogenic modification – catchment and river use (water level controls, floodplain surface land use, floodplain connectivity)
• Restoration factors – aspects of the channel and valley floor to restore (channel form, floodplain connectivity i.e. laterally detached, perched, entrenched)
• Constraints and opportunities – the current functions of our rivers and valleys (built, planning and designation, land ownership and land use, downstream communities at risk)

Mapping was based around data availability, but aimed to use Open Source mapping data as much as possible. The fundamental concept is the Valley Bottom Floor (VBF) as this provides the blank canvas for identifying opportunities. Peter used an index of flatness which was a 2D assessment of the valley bottom looking for changes in slope. This helped define the area or ‘canvas’ upon which opportunity mapping was derived. (Image – red flattest areas, green next flattest areas).

The mapping divided the landscape into 100m² grid squares, and considered all 4 elements in a score for each square (absence/presence of an element). The aim of this mapping approach was not to create a specific map, but generate a map showing a range of suitable sites for floodplain reconnection. This is a strategic tool to help the decision-making process and highlight areas to investigate further.

Peter finished by outlining how the mapping can be used as an application for delivering floodplain reconnection:

• Desk based study – define the VBF, identify the functional and process-based elements (what’s your blank canvas), interpret the database of elements to help characterisation
• Design – consider how the restoration is going to work in practice. E.g. online reconnections mean the floodplain flows settling out laterally are going to have to return that water to a single thread again at some point downstream. Consider how/where to reconnect and where to source water from
• Implementation – understanding of site characteristics. Consider what type of work is more appropriate – nature-assisted, process-based work (woody material in stream, and existing habitat enhancement); or heavy machinery (digger, infilling channel, re-sculpting floodplain)

Stage 0 form is about creating habitats, wetlands, wet woodlands. The interaction between river and floodplain vegetation is important, and we should consider how vegetation can be a driver for the restoration.

Thanks to all involved in hosting and delivering this very informative webinar.

Watch the webinar on YouTube