Managed Realignment Understanding the Development of New Intertidal Processes

In September 2013, the largest open-coast-managed realignment scheme in Europe was breached and Medmerry Nature Reserve created.

Part of the remit of the design of a Managed Realignment (MR) site is that it provides sustainable flood defence as well as becoming a fully functioning ecosystem, both of which rely on the colonisation of saltmarsh flora, which in turn relies on a supply of fine sediment. To achieve long-term sustainability these newly created MR systems also have to deal with the effects of climate change, in other words be resilient to sea level rise and the increases in storminess.

Understanding of the relationship between geomorphological elevation and vegetation is often used as one of the principle tools in the design and construction of these managed realignment sites, but understanding of the geomorphological evolution, response to extreme events and development of abiotic factors in managed realignment sites is incomplete.

The University of Brighton and the Environment Agency have jointly funded this project to monitor and understand the processes as the system transforms from terrestrial to an intertidal habitat. This includes the analyses of data from sampling the intertidal sediment and hydrodynamics along with meteorological data within the new Medmerry site, as well as monitoring small geomorphological changes using specialist bed elevation monitoring equipment together with UAV surveys.

As part of a larger multidisciplinary team, co-ordinated by the Environment Agency, the results from this study will also feed into other research areas (eg. flora and fauna). This multi-disciplinary approach is helping to build up a fuller understanding of the interdependent nature of the development of these type of systems. This will help inform stakeholders on how to improve future coastal management.

This project links directly with the ongoing longer-term monitoring programme (10+ years) in the neighbouring long-term MR site of Pagham Harbour, with data comparisons being undertaken.

This project is still on-going; however, initial published results show that:

• Coastal MR sites evolve at a different rate to estuarine sites as the sediment supply is less
• During the first few years following breach, sub-surface piping at the edge of the drainage features collapse creating surface drainage paths that can form the start of embryonic channels.