Pontee N. - CH2M and University of Southampton
A recent example of large-scale habitat restoration in the coastal zone can be found in an account by James Scott (CH2M) and co-authors (2015) on the Steart Coastal Management Project (see Coastal Management, Changing Coast, Changing Climate, Changing Minds. Institute of Civil Engineers Publishing). The project was developed by the Environment Agency, Wildfowl and Wetlands Trust (site managers), CH2M (Consultants) and Team Van Oord (Civil Engineering Contractor).
About 100 hectares of saltmarsh are being lost each year in the UK. This is due mainly to the combined effect of sea level rise and flood defence projects (coastal squeeze). In order to provide compensatory habitat a large-scale salt marsh restoration project has been initiated on the Steart Peninsula in the Bristol Channel at its confluence of the River Parrett (Figure 1). The scheme area covers around 600 hectares most of which was formerly used for agriculture. Almost 300 hectares of intertidal salt marsh and mudflats have been created together with 70 hectares of transitional brackish habitat and over 100 hectares of coastal grazing marsh and freshwater habitat. The project is one of the largest habitat creation schemes ever undertaken in the UK.
Figure 1. Steart Peninsula in the Bristol Channel. Photo credits to Sacha Dent WWT.
The project was led by the Environment Agency and took more than 16 years to set up (1998 to 2014). Through a competitive process the Wildfowl & Wetlands Trust (WWT) were selected to deliver the project and guide the scheme through all the legal and regulatory challenges. A Master Plan for the Steart Peninsula was developed by the WWT with the Environment Agency and the Bristol Port Company and the project was put into effect three years later in 2014.
Key to the success of the project was wining and retaining the trust of the local residents. A small collaborative working group was set up and major stakeholders and individuals were invited to comment on the scheme’s development. The formation of strong and open relations allowed concerns or opposition to be addressed and enabled optimal plans to be developed quickly with the understanding and support of the local community. Sites of Special Scientific Interest (SSSIs), Special Protection Areas (SPAs), Ramsar Sites and Special Areas of Conservation (SACs) were safeguarded through detailed design and assessment and consultations with local authorities.
In the design of the restoration project extensive modelling was undertaken by CH2M to evaluate tidal inundation characteristics and to assess the impacts on the surrounding estuary. Multiple options were considered, including seaward breaches, multiple estuary breaches and a single breach into the estuary. Hydrodynamic modelling showed that some scheme designs produced increases in tidal levels within the estuary if implemented. Through the modelling the optimal setting for a single northerly breach into the River Parrett was chosen which avoided increases in flood risk.
3D computer modelling was used to plan the earthworks and manage risk. The model ensured that all the material excavated was accounted for, haulage routes were minimised and that special wildlife areas, archaeological features and sites important to the local community were avoided.
A ‘herring bone’ artificial creek system was designed for the site (Figure 2) to distribute water into the farthest parts of the site, allow the site to drain, aid the development of creeks and consequently permit the new salt marsh habitat to form. The creek network was also designed to be constructed safely, maximise the area and diversity of intertidal habitat created, minimise adverse environmental impacts, minimise whole-life costs and achieve an aesthetically pleasing landscape. Ensuring that the project did not impact on landowners or the critical drainage function of the area beyond the confines of the site presented considerable challenges. More than 100 structures were designed to manage water and access across the scheme.
Figure 2. Steart Marshes from the air . Photo credits to Sacha Dent WWT.
The artificial creeks were constructed using a 3D model combined with GPS enabled earthmoving equipment. This allowed the earthworks to be constructed accurately whilst at the same time reducing equipment movements and reducing environmental impacts.
In the last 3 years the creek system has evolved. Some creeks are cutting back and deepening and new smaller creeks are forming. The creeks are being cut back in a similar fashion to a river system eroding a hard substrate.
Additional advantages of the scheme include 1) capturing hundreds of tons of carbon in the accumulating sediments, 2) providing habitat for the breeding of commercial fish stocks, 3) restoring a natural environment for wildlife conservation and 4) stimulating tourism through new visitor car parks and informative signs. The site is now the focus of a number of long-term scientific studies by the University of Southampton, Manchester Metropolitan University, Oxford Brookes University and Plymouth University on sediment accretion rates, carbon storage estimates, fisheries, nutrient regeneration, species succession, microbial interactions and the valuation of ecosystem services to quantify the benefits of restoration actions.
For further information contact Nigel Pontee (firstname.lastname@example.org), Global Technology Leader, Coastal Planning and Engineering, CH2M and Visiting Professor, Natural and Environmental Sciences, University of Southampton.