Glenn-Marie Lange

The effectiveness, costs and coastal protection benefits of natural and nature-based defences

There is great interest in the restoration and conservation of coastal habitats for protection from flooding and erosion. This is evidenced by the growing number of analyses and reviews of the effectiveness of habitats as natural defences and increasing funding world-wide for nature-based defences–i.e. restoration projects aimed at coastal protection; yet, there is no synthetic information on what kinds of projects are effective and cost effective for this purpose. This paper addresses two issues critical for designing restoration projects for coastal protection: (i) a synthesis of the costs and benefits of projects designed for coastal protection (nature-based defences) and (ii) analyses of the effectiveness of coastal habitats (natural defences) in reducing wave heights and the biophysical parameters that influence this effectiveness. We (i) analyse data from sixty-nine field measurements in coastal habitats globally and examine measures of effectiveness of mangroves, salt-marshes, coral reefs and seagrass/kelp beds for wave height reduction; (ii) synthesise the costs and coastal protection benefits of fifty-two nature-based defence projects and; (iii) estimate the benefits of each restoration project by combining information on restoration costs with data from nearby field measurements. The analyses of field measurements show that coastal habitats have significant potential for reducing wave heights that varies by habitat and site. In general, coral reefs and salt-marshes have the highest overall potential. Habitat effectiveness is influenced by: a) the ratios of wave height-to-water depth and habitat width-to-wavelength in coral reefs; and b) the ratio of vegetation height-to-water depth in salt-marshes. The comparison of costs of nature-based defence projects and engineering structures show that salt-marshes and mangroves can be two to five times cheaper than a submerged breakwater for wave heights up to half a metre and, within their limits, become more cost effective at greater depths. Nature-based defence projects also report benefits ranging from reductions in storm damage to reductions in coastal structure costs.

Natural Capital, Total Wealth and Sustainable Development in Namibia

A country’s income and economic well-being depend on its wealth, where wealth is defined in the broadest sense to include produced, natural, human and social capital. Recognising this, international agencies have begun to shift their emphasis from economic development as Gross National Product (GNP) growth to economic development as a process of ‘portfolio management’ that seeks to optimise the management of each asset and the distribution of wealth among different kinds of assets. In resource-rich economies such as Namibia, building national wealth requires that natural capital be transformed into other forms of capital. However, there has been growing concern that economic growth, especially in resource-rich developing countries, has been achieved by liquidation of natural capital without adequate provision for replacement of these assets for future generations. Several studies have attempted to measure total national wealth or changes in wealth but have been seriously hampered by a lack of data, especially for natural and human capital. Using newly available accounts for natural capital in Namibia, total national wealth accounts are constructed and used to assess its development paths, comparing it to its neighbour, Botswana, for which total wealth are also available, albeit not for as long a time series. In Namibia’s pre-independence period (before 1990), there was significant liquidation of capital, natural and produced. With new policies and a new investment environment since independence, Namibia has slowly started to rebuild its national wealth although per capita wealth has not recovered to the level of 1980.