Table. 1 Strengths and weaknesses of different coastal defence options
| Â | Hard measures | Natural measures | Soft measures | Hybrid measures |
|---|---|---|---|---|
Strengths | - Long experience in design and implementation84. - Substantial evidence base about the types, functions, protection mechanisms and capacity, and potential risks of different structures11. - Immediate effectiveness after construction (MA), which makes them suitable for high-risk contexts7. - Possible suitability for areas with limited space13. - Positive economic return on investment (MA) | - Possible self-adaptiveness to changing climate and self-recovery after disasters9. - Provision of multiple co-benefits, including climate change mitigation and risk reduction (MA), human wellbeing and biodiversity conservation9. - No investment costs and very high economic benefits22. | - Possible self-adaptiveness to changing climate and self-recovery after a disaster9. - Provision of multiple co-benefits, including climate change mitigation and risk reduction (MA), human wellbeing and biodiversity conservation9. - Restored habitats are more effective in risk reduction with time7. - Positive economic return on investment (MA) | - Flexibility in combining hard and soft measures, which allows for innovative context-specific practices when designing coastal defence11. - Provision of multiple co-benefits, including climate change mitigation and risk reduction (MA), human wellbeing and biodiversity conservation9. - Greater confidence in shoreline protection by harnessing the advantages of both hard and soft measure25. - Suitable for contexts characterised by low-to-high risk urgency (MA). - Positive economic return on investment (MA) |
Weaknesses | - Lack of self-adaptiveness to changing climate11. - High environmental risks (e.g. structures damage natural habitats or degrade water quality)13. - Failure to provide co-benefits associated with climate change mitigation, human wellbeing and biodiversity conservation (BL). - Possibility of creating perceptions of false safety to local communities11. | - High vulnerability to the rapid degradation of natural coastal habitats worldwide21. - Substantial recovery time following degradation by natural or human processes7. - Insufficient for high-risk coastal zones7. - Significant space requirement for implementation, which makes them possibly unsuitable for dense urban areas11. | - Long time requirement to reach maturity and provide risk reduction benefits equivalent to hard structures50,51. - Effectiveness is highly dependent on ecosystem type (Fig. 2) and ecological support of the local environment59. - Lack of suitability for areas that cannot support ecosystems11. - Significant space requirement for implementation, which makes them possibly unsuitable for dense urban areas11. - Distinct human-nature interactions during implementation59. | - Limited implementation due to knowledge, expertise, and experiences globally (BL). - Substantial effort requirement from different stakeholders (e.g. academics, policy-makers, private sector, local communities) to design the best hybrid measure in a given context59. - Negative environmental impacts of the grey infrastructure component7. - High uncertainty over operational parameters and effectiveness during implementation7. - Distinct human-nature interactions during implementation59. |
