Nature-Based Engineering: A Review on Reducing Coastal Flood Risk With Mangroves

Abstract

Integration of mangroves in projects to reduce coastal flood risk is increasingly being recognised as a sustainable and cost-effective alternative. In addition to the construction of conventional hard flood protection infrastructure, mangroves not only contribute to attenuating flood events (functionality), they also recover in, and adapt to, a changing climate (persistence). The implementation of mangroves in flood risk reduction, however, remains complex. This is because the innate functionality and persistence of mangroves depend on a range of environmental conditions. Importantly, mangroves may collapse when environmental impacts or climatic changes exceed key system thresholds, bringing uncertainty into a situation where failure could endanger lives and livelihoods. The uncertainties in mangrove functionality and persistence can be dealt with by (1) improving insights in how ecological and physical processes affect mangrove functionality and persistence across scales, (2) advancing tools to accurately assess and predict mangrove functionality and persistence, and (3) adopting an adaptive management approach combined with appropriate engineering interventions to enhance mangrove functionality and persistence. Here, we review existing evidence, monitoring techniques and modelling approaches from the viewpoint of mangrove functionality and persistence. Inspired by existing guidelines for Nature-based Solutions (NbS) to reduce flood risk, we provide an operationalization for this new approach. In addition, we identify where further research efforts are required for the practical application of mangroves in coastal flood risk management. Key aspects in the variability and uncertainty of the functionality and persistence of mangroves are their failure and recovery mechanisms, which are greatly site- and storm-specific. We propose five characteristic damage regimes that result in increasing reductions of mangrove functionality as well as post-storm recovery periods. Further research on the quantification of these regimes and their thresholds is required for the successful integration of mangroves in coastal flood risk management. Ultimately, the key challenge is the development of adaptive management strategies to optimise long-term mangrove functionality and persistence, or their resilience. Such adaptive strategies should be informed by continued mangrove functionality and persistence assessments, based on continued monitoring and modelling of key mangrove thresholds, and supported through well-established guidelines.

Implications of Coastal Conditions and Sea‐Level Rise on Mangrove Vulnerability: A Bio‐Morphodynamic Modeling Study

“…In addition to more complex hydrodynamics, vegetation attributes such as mangrove stem density and the aboveground root system also affect sediment accretion over the vegetated flats (Kumara et al., 2010 ; Quartel et al., 2007 ; Xie et al., 2020 ), which eventually determines the overall functionality of mangrove forests and their capacity to provide coastal protection against the risk of flooding (Gijsman et al., 2021 ). Previous research has highlighted that dense mangrove vegetation contributes to sediment accretion in the seaward region of the forest, limiting landward sediment accretion and resulting in strong spatial variations in bed level changes, in turn controlling profile shape.…”

Green Nourishment: An Innovative Nature-Based Solution for Coastal Erosion

“…Once being eroded or buried, the seagrass can no longer provide protection to the coast, which is not accounted for at the moment. The green nourishment proposed in this study could be combined with other nature-based solutions, such as beach nourishment, salt marsh construction (i.e., the Marconi project at Delfzijl Netherlands; Hu et al, 2015Hu et al, , 2021Baptist et al, 2021) and mangrove development (Gijsman et al, 2021), to mitigate the coastal erosion.…”

Tale of Two Cities: How Nature-Based Solutions Help Create Adaptive and Resilient Urban Water Management Practices in Singapore and Lisbon

“…Currently, Singapore has an estimated area of 8.1 square km of mangrove forest coverage, equivalent to 1.1% of the country's total land area [15] (Figure 5). This combination of hard and soft engineering solutions could be effective to mitigate coastal erosion and to protect the coast from sea level rise [34]. With the recognition of the importance of these coastal ecosystems, mangrove restoration in Singapore is being actively undertaken through multi-stakeholder and collaborative projects such as the Coastal Protection and Restoration of Mangrove Biodiversity at Pulau Tekong and Restore Ubin Mangroves Initiatives (R.U.M) on Pulau Ubin [35,36]…”