Fish communities have been investigated using seine and fyke net surveys. Seine nets were used to sample fish moving onto the foreshore with the incoming tide, while fyke nets were deployed to capture fish using the intertidal habitats during inundation. Fish were identified to species level, counted and measured before being returned to the river.

The surveys have been used to examine fish abundance, species richness, community composition and fish size, and to investigate how different types of created intertidal habitat are used by fish.

These surveys provide an important baseline for understanding how engineered habitats contribute to fish communities in the Thames Estuary and complement newer approaches such as environmental DNA (eDNA) monitoring.

Fish surveys between 2017 and 2026 recorded 1,388 fish from 14 species across 9 sites. The communities were dominated by common goby and juvenile European seabass, with European eel also regularly recorded. These results indicate that engineered intertidal habitats are being used as nursery areas by fish, including juvenile life stages.

Fish communities differed according to habitat design, suggesting that the way an intertidal habitat is constructed can influence which fish use it. Naturalised set-back habitats supported particularly high numbers of common goby and juvenile European seabass, while European eels were strongly associated with vegetated intertidal terraces.

The surveys also showed that physical connectivity and drainage are important. Sites with channels providing easier access between the river and intertidal habitat supported greater fish use, while structures such as barriers and vertical sheet piling could restrict fish movement or cause fish to become stranded as the tide receded.

Overall, the findings demonstrate that well-designed intertidal habitats can provide valuable habitat for fish in the Thames Estuary, while also highlighting opportunities to improve existing sites and inform the design of future Estuary Edges.

To find out more:

• 2017: Colclough, S., & Cucknell, A. Estuary edges: A survey of fish populations associated with a series of artificial habitat structures in the Thames Estuary. Thames Estuary Partnership.
• 2024: Bodnar, W., Colclough, S., Pryor, A. Fish utilisation of bioengineered intertidal habitats in the Thames Estuary. The London Naturalist 103: 94-112.

An ongoing PhD research project funded by NERC is investigating how fish communities respond to different types of intertidal habitat in the Thames Estuary.

The research combines environmental DNA (eDNA), fish surveys and environmental data to understand how natural, degraded, restored and created habitats, including 13 Estuary Edges sites, are used by fish, and how habitat creation can support fish communities.

The research aims to provide evidence to inform the habitat creation design, restoration, and monitoring of intertidal habitats across the Thames Estuary.

To find out more, visit: wandabodnar.github.io/phd/

• Environment Agency (2011) – Delivering benefits through evidence: Alternative hardwood timbers for use in marine and freshwater construction, Project: SC070083/R1, Flood and Coastal Erosion Risk Management Research and Development Programme. April 2011.
• Environment Agency (date unknown) – National Encroachment Policy for Tidal Rivers and Estuaries.
• Naylor, LA., Kippen, H, Coombes, MA., et al. (2017). – Greening the Grey: a framework for integrated green grey infrastructure (IGGI). University of Glasgow report.
• Wade, T., Hawes, J. and Mulder P. (2017) Middle Thames Tideway – Cumulative effects of re-use, desalination and DRA WRMP19 options, Ricardo consulting working on behalf of Thames Water Utilities Ltd, 26th June 2017.

Government guidance on biodiversity now requires developers to protect and enhance biodiversity in their schemes, particularly priority habitats such as mudflats and saltmarsh. Estuary and river edge design must improve the environment for fish and other wildlife, as well as meet national, regional and local Biodiversity Action Plan targets.

First of all, what is the ‘estuary edge’? As a minimum this should be the entire zone set by the byelaws relating to Flood Risk Management (Land Drainage) consent under Schedule 25 of the Water Resources Act (1991). On parts of the tidal Thames, for example, this extends 16 metres from the inland limit of any statutory flood defence.

National policy – The national encroachment policy for tidal rivers and estuaries states that development should not encroach further into the river channel or estuary.

European policy – The European Unions’ Water Framework Directive highlights the need for maintaining and improving the ecological value of rivers, estuaries, lakes and coastal waters. Itdiscourages actions that would reduce this value.

Further key elements of the main policy and legal framework for estuary edge design in the UK are summarised in Building a better environment: A guide for developers. These include:

• Making Space for Water –the Government strategy that promotes retreat of estuary edges for environmental gain as well as flood risk management.
• PPS9: Biodiversity and Geological Conservation (Section 2.2.4) –this emphasises the need to ensure ecological enhancement in UK development projects of all kinds.
• The Natural Environment and Rural Communities Act 2006 –this has given a duty to all public authorities to conserve biodiversity so far as consistent with carrying out their other functions (this relates fundamentally to the National Biodiversity Action Plan).
• PPS1 Delivering Sustainable Development and Planning and Climate Change –these provide policy support for the wider benefits of ecologically designed estuary edges.

A general approach to sustainable development is explained throughout Building a better environment: A guide for developers. The policies and licensing requirements of the local Navigation Authority should also be consulted. You should also check whether local policies promote particular estuary edge designs. For example the London Plan requires that new development be set back from the river and estuary edge for reasons of flood risk management and the environment.

Building a better environment: A guide for developers discusses the relevant Environment Agency permissions. Developments concerned with building in, over, under or beside our tidal rivers and estuaries will require flood risk management permission through local byelaws (in addition to planning permission from the local authority). The Environment Agency can recommend approval or refusal of applications or request planning conditions and legal agreements to be attached to any planning permissions granted. Consents issued by others that may be necessary for working on estuary edges may include (but may not be limited to):

1. Planning Permission from the Local Authority.
2. Marine Licence from the Marine Management Organisation.
3. Local Navigation or Harbour Authority Consent.
4. A Rights of Way Diversion Order from the Local Authority or Highways Authority (for example, where a footpath or track follows the river or estuary edge).
5. Natural England where works may affect a site carrying a statutory designation for nature conservation (for example, Ramsar Site, Special Protection Area, Special Area of Conservation, Site of Special Scientific Interest, Marine Conservation Zone or Local Nature Reserve) and licences where certain legally protected species might be affected.

While these existing examples of the terraces are now established ways of working, if the site is constrained or not working on the river wall they are not always possible. There are a number of other alternatives that have been trialled in the estuarine environment that will bring ecological benefit to the habitat and species.

The update of the project has not monitored these on the Thames or elsewhere, however there are other projects that have done so are listed in the references below.

Grey infrastructure

Any wall or construction surface should be roughened, at a low cost to facilitated seaweed and algae to colonise. Larger spaces and hollows can allow trapped water and ecology, however if these are near navigable areas these might cause vessels to be damaged if not appropriately marked.

Simple roughing of the edges and surfaces for example, leaving concrete unsmooth can allow algae to populate surfaces not previously available.

Piers and Jetties

Where a site might be more mid river, a terrace becomes an unlikely solution, but there is still a lot that can be done.

• Boxes of sediment and appropriate vegetation for the flow and location. These are similar to window boxes small containers can be fitted to piled structures at various points of the tide, providing they are protected and not impacting on the safe operating of the site
• Roughing the edges and surfaces of the water structure, for example the edges of the pontoon or around the piled structure
• Areas for roosting or nesting birds, providing there is not an impact on safe use of the site for workers and the public. This can be provided by creating gravel mats on structure as small as a pile top, or as large as a green/brown roof. These have additional benefit of reducing run off from the site, but could reduce the amount of space of renewable energy generation by wind and solar in similar spaces.

In the case of jetties and in cargo handling sites, these need to be flush against the walls, for example horizontal timbers between fenders, so that there is no interference with the operation of the site. Maintenance of these additional enhancements must be monitored continually in order that they do not fall into disrepair for the lifetime of the structure and enhancement.

Sea walls

In outer parts or less urban estuary a flood defence is often a series of walls hidden under ground. Design of the mounds for biodiversity as well as the protection required can have significant difference to connections along the estuarine and marine habitats. Different slopes can be important for the energy in the estuary for the function of the structure, combined with rough substrate is key to allow the variation in energy, flow and light in the intertidal areas more diverse that a completely sterile defence. Size of the substrate has to be carefully chosen to balance the energy and typically types of substrate found in the estuary. This is not always possible to match and there may be a need for a compromise.

Useful links and references

Greening the Grey: A Framework for Integrated Green Grey Infrastructure (IGGI)

Green approaches in river engineering

Living Seawalls — Australia

Living Ports / Seawalls — Spain

Enhanced Port Quay Walls — Netherlands

Living Breakwaters — United States