Sunday, April 3, 2011

Coastal protection: costs and benefits of managed realignment

Researchers have examined two cases of managed realignment in the UK, whereby coastal areas are deliberately flooded to recreate protective salt marshes. They demonstrated that a sequential decision support system (DSS) can be combined with an ecosystem services approach to provide a robust economic valuation of managed realignment’s benefits. For the case studies analysed, the benefits of managed realignment were found to outweigh costs in the long-term.
Tidal ecosystems are being lost as they are squeezed between rising sea levels and man-made coastal defences. Managed realignment – deliberately weakening sea defences – can benefit coastal regions, but only under specific conditions. Its aim is to restore areas of tidal habitat in the form of salt marshes, which provide a natural barrier to coastal flooding, reducing the cost of maintaining sea walls and other coastal defences. However, managed realignment can be costly in other ways as land is lost and people are displaced by the returning sea, so a thorough analysis is essential before any scheme is put in place.
The researchers modelled the potential costs and benefits of managed realignment in two case studies over periods of 25, 50 and 100 years. The first case study was an existing study of the Humber estuary, which is 147km long and contains a number of important wildlife habitats. The second case study was a new study of the Blackwater estuary, a 20km long estuary in the south east of the UK.
The researchers first developed a conceptual framework for valuing ecosystem services provided by the estuaries, which they applied in combination with a sequential DSS. The sequential DSS ensured that the economic valuation of ecosystem services considered a number of different factors, including the varying spatial distribution of ecosystem services, complex relationships between estuary characteristics, threshold values (the point at which an ecosystem tips into an alternative state), small changes and ensuring the studies avoided double-counting costs and benefits. A cost-benefit analysis was conducted for each estuary and the results were presented as a series of ‘net present values’ (NPVs).
They found that the NPV for managed realignment in both estuaries was positive, thanks to the ecosystem services they provide. Positive NPVs show that over time, the economic benefits (including ecosystem services) of managed realignment outweigh the costs. Services identified included recreation, enhanced carbon sequestration and, in the Blackwater estuary, fish nursery benefits.
The Humber estuary’s NPV was positive for timescales longer than 25 years. Thus the results suggested that managed realignment in the Humber estuary would be of benefit, but only in the long-term.
The Blackwater estuary case study showed a much stronger benefit from MR over all of the timescales tested. For example, under one of the managed realignment scenarios, the NPV for Blackwood was £156.21million, compared to the Humber’s £3.79million. The analysis also identified costs common to most managed realignment schemes, such as the cost of implementation and the loss of agricultural land.
However, the researchers caution that their study only considered using managed realignment in agricultural areas, where it would not affect many homes or urban areas. The benefits may be significantly less where it could put larger numbers of people, property and other assets at risk. Managed realignment schemes therefore need to be valued on a case-by-case basis.
Source: Luisetti, T., Turner, R. K., Bateman I. J., et al. (2011) Coastal and marine ecosystem services valuation for policy and management: Managed realignment case studies in England. Ocean & Coastal Management. 54: 212-224.

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