Sedimentation fields: human activity, maintenance and the implications for successful saltmarsh restoration

Saltmarsh habitat provides important ecosystem services such as water quality regulation, carbon sequestration, and flood defence. Marshes are also experiencing significant losses globally. One method of restoring saltmarsh habitat is the use of structures such as sedimentation fields to enclose areas of mudflat and encourage sediment deposition. Sedimentation fields offer opportunities for restoration in areas that are unsuitable for other, more common, restoration methods such as managed realignment. They can also provide protection for fixed engineered defence structures such as sea walls. However, sedimentation fields have predominantly been studied using numerical models or with a focus on vegetation colonisation. Therefore, it remains unknown whether the restored habitat can become self-sustaining through biophysical feedback processes accelerating vertical marsh buildup or whether there is a need for continued maintenance to prevent erosion of the deposited sediment.

 

This study presents findings from an empirical investigation of Rumney Great Wharf, Wales. Sedimentation fields were constructed here between 1989 and 2005, but since 2010 no maintenance has been carried out with fencing being eroded and lost. This allows for assessments of whether the restored area is self-sustaining or if continued maintenance is required. We show that 87% of the total area enclosed by sedimentation fields experienced erosion between May 2023 and 2024. This is despite sediment trap measurements indicating the potential for sediment to accrete at more than 9 cm/year. Trends in sedimentological processes are contextualised using depth, current velocity, wave action, and suspended sediment data. Our findings are evaluated in terms of the requirements for further research into sedimentary processes operating in sedimentation fields.

 

Using the insights gained from our study, we discuss the need to consider sedimentation fields as a continuation of human activity influencing natural processes, rather than the removal or reversal of the influence of prior human activity. We emphasise the need for transdisciplinary approaches to (i) develop further understanding of the interactions between physical and biological processes to enhance ecosystem functioning in sites restored using sedimentation fields, and (ii) to inform the design of future schemes. Further research is needed to fully justify the implementation of future sedimentation field construction, identify suitable locations for such schemes and inform their management, and to ensure such schemes provide a nature-based solution to coastal management challenges.