Managed realignment as a tool for compensatory habitat creation – A re-appraisal

Managed realignment has been used to compensate for loss of mudflat and saltmarsh habitat associated with several important port developments in the UK and other parts of northern Europe. It is also closely linked to flood risk management strategies in England. This paper explores some the outcomes of such measures in the Humber Estuary (UK) and considers the implications for future decision-making. The position of realignment sites within the tidal frame means that they will almost invariably form saltmarsh in estuaries with high levels of suspended sediment. The same outcome can be expected elsewhere but the time involved is much longer. Furthermore, realignment sites can only ever replace habitat within the upper levels of the tidal frame and consequently losses of habitat at lower elevations cannot readily be replicated.This analysis argues that whilst realignment is a viable means of addressing certain types of habitat loss it cannot be regarded as a universal solution. More thought needs to be given to the long-term evolution of realignment sites as habitat for feeding migratory waterfowl. This conclusion has an important bearing on the delivery of no net loss of functionality within estuaries designated under UK and European legislation for the migratory waterfowl that they support. It does not exclude managed realignment as a component of compensatory habitat creation. Realignment continues to offer the main means of creating new inter-tidal habitat. There will, however, be circumstances where offsetting measures cannot be relied upon without sites being considerably bigger and conforming to a more complex suite of design parameters. This paper offers a provisional checklist of where and when realignment is appropriate as an offsetting measure.

► The rate of saltmarsh development within managed realignment depends upon sediment supply.
► Only the upper levels of inter-tidal habitat can be created by managed realignment.
► This means that lower level mudflats cannot be replaced by managed realignment.
► Bigger realignments will provide longer-term solutions but even these are time-limited.
► Realignment has restricted application in the context of the EU Birds and Habitats Directives.