Growing with the flow: Investigating nature-based approaches to mitigate flooding in the Pacific Islands

Human activities are pushing planetary boundaries, causing both climate and biodiversity crises. Flooding is now the most common naturally-triggered disaster worldwide and is predicted to worsen in many regions. Recently, nature-based solutions (NbS) have gained increased attention as an approach to address these challenges. NbS can reduce flooding through attenuation, reducing erosion and increasing infiltration, whilst supporting, enhancing, and protecting ecosystems - often referred to as ‘Natural Flood Management’ (NFM). However, much remains unknown about NFM effectiveness, including how resources can be optimised, particularly at catchment scale. Many Pacific Islands are vulnerable to flooding, exacerbated by changes in land cover and population increase, and sea level rise. Currently, there is a limited body of work on the role and diversity of NbS in reducing fluvial and pluvial flooding in tropical island contexts. This thesis reviews and evaluates current practice and introduces new quantitative and qualitative methodologies to support decision-making processes with applicability worldwide. Modelling NFM is a key challenge, but recent advances in remote sensing, flood modelling software and computational power enable new insights. Here, source-to-impact flood analysis is applied to better identify where NFM can reduce flooding the most in a catchment. Sensitivity analyses were undertaken, and a range of scenarios were modelled, including changing rainfall patterns, NFM scales and NFM intensities, using a new numerical method which, using the software HEC-RAS, analyses how NFM effectiveness varies when applied to any site in a catchment to understand impacts on NFM effectiveness. The key findings of this modelling were that NFM can increase lag time, reduce peak flows (with the magnitude of flow change being proportionally greater for smaller events) and additional peak flow reduction benefit may be gained when NFM implementation is undertaken in combination across multiple sites. This new numerical method is also compared for the first time to the most frequently used tool for choosing NFM sites, that is, multi-criteria analysis, which highlighted the importance of land cover and infiltration parameters. Finally, given a gap in literature on temporal NFM dynamics, a discussion on how NFM changes with time is provided. The research also applies a socio-cognitive model to NFM, using the Risk-Attitude-Norms-Ability-Self-Regulation (RANAS) approach. This method was used to better understand flood and catchment practitioner NFM approaches through interviews, in Fiji and the Cook Islands. NFM enabling factors were identified including funding, technical knowledge and cultural aspects, including traditional and local knowledge in Pacific Island geographies. This thesis builds on a growing body of research demonstrating how NbS can be applied more effectively, particularly in remote and tropical regions that are highly vulnerable to climate change and where data access can be challenging. The research highlights the importance of integrating NFM with wider catchment benefits and community decision making, whilst offering practical recommendations to support implementation.

Grantor dc:publisher

UNSW, Sydney

Year dc:date

2025

Author dc:creator

• Earl, Eleanor

• Pacific Islands
• Nature-based
• flooding
• catchment
• anzsrc-for: 400513 Water resources engineering
• anzsrc-for: 4101 Climate change impacts and adaptation
• anzsrc-for: 4102 Ecological applications
• anzsrc-for: 4515 Pacific Peoples environmental knowledges
• anzsrc-for: 41 ENVIRONMENTAL SCIENCES

Statement dc:rights

• open access
• CC BY 4.0
• free_to_read

Licence

• https://purl.org/coar/access_right/c_abf2
• https://creativecommons.org/licenses/by/4.0/

Language dc:language

en

Identifier

https://doi.org/10.26190/unsworks/31987

OAI identifier oai:identifier

oai:unsworks.library.unsw.edu.au:1959.4/106923