Coastal ecosystems and landforms are critical parts of resilient coastlines, buffering environmental hazards, sequestering carbon, forming natural habitats that support global biodiversity, and providing recreational spaces and livelihoods. Yet coastal zones are increasingly exposed to human and environmental pressures from sea level rise, and more intensive storms due to climate change.
There is a growing interest in the role that large-scale nature-based solutions can help resilient dynamic coastal systems. Such schemes aim to work with natural processes and take a longer term view that is cognisant of sediment transport, ecological, and hydro-dynamic processes and their impact on flood and erosion risk. Studies have shown that such schemes are very cost-effective, and the UK Government now has ambitious goals for the restoration of natural intertidal buffer systems, such as dunes and saltmarshes. The Committee on Climate Change estimates the latter to lead to a cost saving of up to £33 billion compared to traditional hard defences.
But these are new approaches and so it is vital that schemes are monitored to see how they perform, and guide future actions to ensure the potential economic, social and ecological benefits are realised. Earth observation data is ideally suited to such monitoring efforts.
One of these new techniques is the “sand engine” approach used already to manage dynamic coastlines in the Netherlands. The approach collects sand, dredged offshore, and places it on the shoreline, to allow the waves, wind and currents to move the sand. The process takes place over a number of years and realigns the coast as well as providing a range of environmental, societal and economic benefits.
The approach was adapted for use in North Norfolk, where nearly 2 million cubic metres of sediment was deposited in the intertidal zone at Bacton during summer 2019 (Figure 1) to extend the width and height of the beach, at a cost of around £18 million. This was undertaken as part of the Bacton to Walcott Coastal Management Scheme (BWCMS) to protect the Bacton Gas Terminal, the villages of Bacton and Walcott, and to extend the life of the villages’ sea defences. The Bacton Gas Terminal is critically important, supplying up to 30% of the UK’s gas demand, and storm damage would cause huge costs and considerable disruption, potentially to the whole of the country.
The Eye in the Sky
To assess if the sandscaping was working as planned, elevation profiles were recorded to demonstrate the change across the beach. Profiles were taken using traditional surveying practices: but these provide point measurements, widely spaced, which is not ideal given the very dynamic environment and large scale nature of the scheme. Regular monitoring of large areas in this way is also prohibitively expensive.
However, monitoring the change in beach elevation using remotely sensed monitoring data from satellites that pass overhead daily could be an ideal approach.
A Sentinel 2 L2 satellite image of Bacton and the shoreline
Geoger, with project partners, developed a way to use high temporal frequency and high spatial resolution optical Earth observation data to capture the complex changes caused by the scheme relative to the areas of infrastructure and settlements being protected. Using these image data and sea level information, the consortium produced a set of 3-dimensional morphological and elevation models that show change in the structure of the beach over time. The models were checked against three beach survey profiles and showed a comparable accuracy.
The satellite images below are overlaid with the derived elevation models for periods before, during and two to three months after the sandscaping event. The highest areas of the beach are shown in yellow and the lowest in purple. The effect of the sandscaping can clearly be seen in terms of the change of sediment over time: crucial information for the ongoing management of the shoreline.
It is evident that space data can be used to monitor the impact of the sandscaping and track the subsequent natural movement of the beach sediments. Our approach could provide a monthly interpolated high spatial resolution elevation model across the intertidal zone.
Not only did our method prove that comparable elevation data can be obtained compared to traditional surveys, but it also showed many superior aspects, such as the large area that can easily be monitoring using satellite data, as well as the higher temporal frequency, sampling density, extent and quality of the derived 3-dimensional morphological and biophysical information.
Not only does this approach yield considerable value and insight to the end user but also as well as cost savings compared to traditional approaches, with minimal disturbance to the area and no health and safety issues.
The figure below shows the distribution of some other coastal sites where nature based solutions could be applied to address large-scale coastal erosion, where our approach could be implemented.
The CoDyMon feasibility project was led by Specto Natura Ltd. in collaboration with Geoger Ltd., Trinity College Dublin (TCD), Planet Labs Inc. and Coastal Partnership East (CPE). It was funded by a European Space Agency UK Launchpad Initiative grant managed in conjunction with the Satellite Applications Catapult.