Estuary Edges


Worldwide, many rivers and their estuaries have been straightened and constrained over hundreds of years of development to build our cities and facilitate vital international and national trade. Urban rivers and, in particular, estuaries have been modified the most, retaining little of their natural character or function and unable to deliver the natural services they would have if allowed. These natural services, called ‘ecosystem services’ include aspects such as slowing the flow of water through meanders and habitat; reducing flood risk on the land through holding the water in the floodplain; carbon sequestration, pollution attenuation; improved nursery and spawning grounds for fish; and vital foraging grounds for other wildlife. In addition, they provide services that allow us to enjoy recreation and boost our wellbeing through being close to water – a vitally important role in a heavily urbanised and densely populated area.

Estuaries provide some of the most dynamic and productive yet fragile aquatic environments in the UK.

Estuaries are complex and dynamic, with tides churning the waters, moving nutrients around the whole system – and that is how we need to think about and manage such an environment, as a whole system from tidal limits to global ocean. To manage it in sections or parts means we miss the positive and negative impacts activity and development can have on it and the changes that occur from a changing climate. The whole system is connected and so we need to manage using upstream thinking above the tidal limits to understand the impacts on the tidal areas and downstream to understand the reverse. For example, materials and flora used in river restoration projects in freshwater tributaries upstream can break down or break free and contribute to pollution or invasive colonisation downstream. Finding the balance of using the right materials and techniques in the right places according to local environments and conditions but in the context of the whole system is crucial. In doing so, we can ensure that the principles of Net Gain and integrated water and catchment management can be realised.

There is movement of many elements that make up the whole system. Estuaries provide nursery areas and migration corridors for internationally important fish species of conservation interest e.g. the European eel and Smelt and nationally important commercial stocks of e.g. sea bass and flounder. Many of these species need to move between the marine environment downstream up into the freshwater environment in the upper estuary and beyond as part of their life cycle. Estuaries also provide feeding and foraging grounds to highly mobile species such as dolphins and seals and internationally and nationally important bird species that visit because of the fantastic feeding opportunities estuaries provide through their immense productivity. The mud and turbidity of the water constantly moving nutrients around the whole system is what makes an estuary so biologically productive. The mud is rich in invertebrates which feed the fish and bird populations. Vegetated areas increase both the diversity of invertebrates in the mud and the wildlife that can use it, so native planting or wild colonisation is important.

Within urban environments most estuary edges have been fronted with vertical concrete and sheet steel pile walls to protect the land from water inundation, negatively impacting on their ecology, landscape character and value.

Within the Thames Estuary, running through London, only around 2% of the tidal banks remain as natural (or ‘soft’) in profile (S.Colclough, pers comms.). Furthermore, many estuaries are far narrower than they would naturally be, due to construction into, or over, the bed of the estuary known as ‘encroachment’.. Encroachment typically reduces the amount of water the channel can safely carry, leading to higher water levels, increased velocities, increased risk of flooding and erosion. In addition, it has led to the loss of large areas of tidal foreshore, which is an important habitat of national and international significance. Foreshore areas can also provide precious open space for recreation, and leisure, education and are often of considerable archaeological importance as well as providing a ‘conveyor belt’ of continuous habitat for aquatic species. Confronted with a scenario of climate change and increased sea levels, if the process of encroachment continues unchecked water levels will continue to rise and the foreshore will be lost. It is very important whenever possible that encroachment is halted or reversed and banks are softened to maximise the benefits to us and wildlife.

By periodically reversing encroachment and/or softening banks, we can create a ‘string of pearls’ of habitat which could eventually help to restore our fish populations.

By providing habitat along the edges of estuaries, we will be adding to a ‘String of pearls’ of connected habitat for all flora and fauna helping our wildlife use this migration corridor and ‘super highway’ more easily and naturally.

Furthermore, habitat on the landward side of our estuaries is vital for other struggling species such as bats, bees and insects. Much of the connection between our estuaries and land is disconnected by the flood defences and we have riverside concrete paths where green space could be incorporated as part of a landscape approach. Encouraging greening of our terrestrial riversides adds to the overall diversity of our rivers and improves the human experience. Research shows that combinations of green and blue spaces vastly boosts our mood and is critical to human health and wellbeing. Intertidal habitat can be easily linked with the wider ambitions of greening strategies such as delivering Sustainable Urban Drainage Systems (SUDs) and green corridors. An example of a SUDs system that drains under the Thames Path and through the flood defence into an intertidal terrace is highlighted in one case study (Royal Wharf). An innovative approach that shows how we can connect across our urban landscapes and reconnect to the urban estuary. More approaches like this should be encouraged as solutions to pressing challenges such as increased rainfall and surface water flooding as a result of climate change.

Softened estuary edges along with landward green space, good footpaths and signage help to increase use of the riverside path, boosting health and wellbeing, encouraging increased physical activity to combat obesity, providing opportunities for education and greater understanding of the tidal bank habitats that support estuary wildlife. A good example of signage is at Greenwich Peninsula.

This Website

This website outlines some methods and principles that have been used to reverse the impacts of encroachment and/or soften banks in urban estuaries through clever reconstruction or refurbishment techniques which add value to the development potential of the site. It does so through 17 ‘high level’ design principles (accompanied by more detailed design guidance) with an evidence base from 17 sites throughout the Thames Estuary (see Case Studies). At these sites, ecological, non-ecological and social data have been gathered for the first time in 20 years (see Sampling Methods). We give an overview of how well these sites are performing and make recommendations building on lessons learned from the past. Locating all the sites in one estuary has allowed comparison of data but it does not mean that the methods cannot be used outside of the Thames Estuary. Surveys are continuing as part of the legacy of this refresh of the guidance. Ongoing monitoring is crucial to understand more about our estuaries and continuing to learn how to build better Estuary Edges for all (see Monitoring and maintenance)

As a developer, the choice of method at your site needs careful consideration as one size does not fit all. The localised environmental conditions must drive the selection of design elements and ultimately what will work. However, if delivered in the right way, the feature can achieve economic, social and environmental benefits. Well-planned developments next to our estuaries can create better places to live and work, contributing to people’s health and wellbeing by providing better access to green and blue spaces and opportunities for recreation or quiet resting places. Replacing grey sheet piling with lush colourful plants and swards of reed stems rustling in the wind add significantly to the waterside experience for workers, tourists and residents alike whilst increasing your land and development value. In addition, contributing to the pre and post monitoring of sites will help deliver against the commitments of Net Gain and provide opportunities for communities to get involved in managing and understanding their natural environment.

Including features that improve public access and educate people about the local environment by making the unseen seen will vastly improve the public realm as well as bringing environmental and health and wellbeing benefits.