Flood resilient structures

Traditional building constructed on stilts, “Kanganaman Village – East Sepik Province – Papua New Guinea” photograph by Rita Willaert, CC BY-NC-SA 2.0 via Flickr.

The threat of climate change involves more frequent and severe events. Flooding is the most common natural hazard worldwide. In many parts of Te Moananui Oceania, flooding is a prominent hazard, especially in related to storm surges and sea level rise (Barnett, 2011). NIWA (National Institute of Water and Atmospheric Research New Zealand) show that since 1950, weather-related natural disasters have directly affected more than 3.4 million people in the Te Moananui Oceania region, and that ten of the fifteen most extreme events in the region reported over the past half-century occurred in the last fifteen years (Blackham et al., 2015).

There are various strategies used in construction that can prevent, mitigate, or adapt to the effects of more severe flooding. These include:

Sacrificial ground floors

Sacrificial ground floor constructions are buildings with a lower level designed or modified in a way that allows it to be flooded without causing damage to the overall structure (Cabato et al., 2022). These levels are constructed using materials that can withstand water exposure and can be easily cleaned or repaired after a flood event. 

Elevated construction

Elevated constructions are raised on tall foundations, piles, or stilts above the level of regular flood events (Narayan et al., 2020). This prevents floodwaters from entering the inhabited parts of the building. This strategy is especially relevant in areas of Te Moananui Oceania where sea level rise and storm inundation are major threats, and where semi-permanent buildings are often constructed using local materials, making them adaptable to having new elevated foundations.

Floating buildings

Floating buildings are designed to rise and fall with water levels. These are exceptionally resilient to flooding, often being anchored to a fixed point but able to move vertically to adapt to changing water levels, ensuring that the living spaces remain above the water (Penning-Rowsell, 2020). Floating buildings are relevant in areas with water level fluctuations but generally calm water, such as protected tidal zones, lagoons, or flood plains.

Name of NbS

Flood-resilient structures

Type of NbS

Engineered interventions

Location

  • Urban
  • peri-urban
  • rural

Flood-resilient structures can occur in any context. In urban areas, these structures protect communities susceptible to flooding or can allow construction on marginal land known to flood. In peri-urban and rural areas, flood-resilient structures mean that valuable land for agriculture and other uses is protected from development and that housing can be located in areas less useful for other activities.

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Case Study

Solomon Islands Village Shelters

Framing for a village shelter under construction. Photo from Kaunitz Yeung Architecture, 2024.

Relationship to Indigenous knowledge

Indigenous flood-resilient structures appear globally. There are specific examples of floating Indigenous architecture of the Ma’dan in Iraq and the Uros in Peru for example (Julia Watson, 2020). Despite intimate knowledge and relationships with the ocean, floating architecture is limited in Te Moananui Oceania. Pile elevated structures appear in some parts of Te Moananui Oceania, and research suggests their more widespread use historically in Te Moananui Oceania, with origins in the Lapita culture in Southeast Asia, likely as a response to malaria-causing mosquitoes and other immediate dangers, alongside promoting better ventilation in humid climates (a result of being raised off the ground) (Zamolyi, 2015).

In Fiji, pile foundations over time evolved into raised mound foundations in response to material, climatic, and socio-cultural factors. An architecture that maintains an elevated pile form across several Te Moananui Oceania cultures is the storehouse (Lewis, 2014). A prominent example of this is the Pātaka (Māori raised storehouse). Sacrificial ground floors are a recent development but can be seen in contemporary homes in Kiribati for example.

It is important to note that for some Indigenous people, flood events may not be considered a ‘disaster’, and that before Western scientific studies, Indigenous peoples’ knowledges recognised that floods played a crucial part in maintaining the health and wellbeing of all (human and more-than-human) who dwelled within waterscapes (Parsons & Fisher, 2022). Considering this, flood-resilient structures represent ways to construct or adapt buildings that allow people to remain in place as the preferred response, rather than retreat (Crichton et al., 2020; Narayan et al., 2020), but also to adapt to climate change and other anthropogenic changes that exacerbate the frequency and severity of floods. 

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Climate change benefits
  • Sea level rise
  • Storm surge
  • Freshwater flooding

Flood-resilient structures can directly address the impact of flooding, especially in increasingly urban environments across Te Moananui Oceania. The impacts addressed include sea level rise, storm surge, and freshwater flooding (Blackham et al., 2015; Kiddle et al., 2021). Importantly, using flood-resilient construction methods protects people and property from harm. They also enable marginal land to be utilised, protecting valuable agricultural land from development. 

Flood-resilient housing does not necessarily mitigate climate change, aside from the potential implementation of other sustainable construction measures, nature-based or biomimetic strategies (MacKinnon et al., 2022) and the reduction of the need to repair or rebuild structures after major flooding events.

In atoll islands like Kiribati and some in French Polynesia, floating structures have been suggested as a solution to projected sea level rise and loss of land (RNZ, 2018). There remains many issues around feasibility, sovereignty, geopolitics, and environmental sensibility with such proposals (Mawyer, 2021; Saddington, 2021).

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Societal / socio-cultural benefits
  • Climate change adaptation
  • Disaster risk reduction

Flood-resilient buildings can assist communities in climate change adaption through the modification of existing, or the building of new flood-resilient structures. Flood-resilient construction methods can be employed even for existing buildings, where modification may be more affordable than constructing a new building (English et al., 2018). These strategies can also be used in community buildings to provide a place of refuge, reducing risk for entire communities alongside providing other amenities (Riise & Adeyemi, 2015). Flood-resilient structures require less repair or cleaning after a flood event, reducing the social and economic impact, as well as disruption to day-to-day life (Barsley, 2019; English et al., 2018).

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Ecological and biodiversity benefits
  • Disturbance prevention (erosion, storm damage, flooding etc.)
  • Social justice and equity
  • Recreation and tourism

The benefits of flood-resilient buildings extend beyond flood damage and risk reduction, contributing also to disturbance prevention, and reducing the impact of floods on the built environment and surrounding ecosystems. Elevated constructions and floating buildings reduce the contact between floodwater and structures, reducing the potential for damage, and therefore reducing physical pollution from man-made debris, and pollution from other contaminants of waterways and Oceans. Flood-resilient buildings can address social justice and equity issues by ensuring all community members, especially people who live in vulnerable areas or those who do not have land tenure, have access to flood-safe housing or community buildings to take refuge in. Reducing the impact of floods also reduces displacement and the economic burden related to recovery after a flood event (Barsley, 2019). 

There are numerous examples of elevated construction being used for the construction of tourism accommodation in Te Moananui Oceania, where lodging is built out over sheltered lagoon water, and although these promote recreation and tourism, there is limited research about the direct ecological impacts of these structures.

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Bure house on a rock-face mound (yavu)” (Elkharboutly & Wilkinson, 2022) preventing flooding or overland flow from entering and damaging the building. Photograph from Elkharboutly & Wilkinson, (2022).
Maori storehouse, picture taken around 1950s in Whakarewarewa”. Public domain via Wikimedia Commons
Residential houseboats (fixed floating houses). Seen Middelburg, Netherlands” photograph by W. Bulach, CC BY-SA 4.0 via Wikimedia commons.

Technical requirements

  • Legislative, local planning
  • Materials, floating – stable, resilient
  • Connection to services
  • Sheltered water

There are legislative and local planning requirements that could be barriers to the construction of some flood-resilient structures. Floating construction can have additional requirements. Lack of access to emergency services, limited green space, and minimal setbacks can pose challenges when required to meet local planning laws (Penning-Rowsell, 2020). Materials for strategies like floating structures and elevated construction might be limited in some areas of Te Moananui Oceania, requiring significantly sized timbers to construct pile foundations, or specific materials being required for floating foundations that are stable and buoyant to be imported. Floating constructions also pose specific technical requirements when being connected to services like power, and sewerage, as connections need to be flexible to move with the rising and falling of floodwaters. Floating and elevated structures require sheltered water if they are to be built over an existing water body. Some proposals in Te Moananui Oceania have suggested utilising the sheltered lagoons of atoll islands (RNZ, 2018).

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Issues and Barriers

  • Lack of particular skills
  • Lack of sheltered water areas
  • Prohibitive costs
  • Legislative, local planning
  • Finance and insurance

Issues and barriers to flood-resilient structures include a lack of specific skills locally. Most modern floating buildings have been developed for European countries, particularly the Netherlands (Penning-Rowsell, 2020). Flood-resilient buildings built over water bodies still require relatively sheltered water, like lagoons, lakes, or river deltas, and this is especially true for Indigenous knowledge-based or vernacular examples of architecture (Julia Watson, 2020). The frequency and severity of weather events in most of Te Moananui Oceania is a barrier to construction over water bodies, where storm inundation is likely in open water and storms are becoming more intense (Blackham et al., 2015). Costs to adapt buildings that have utilised other construction methods may be too expensive for many people to implement without support. This is equally true for technology relating to the construction of new floating constructions. 

Legislation and local planning laws can be prohibitive, as flood-resilient buildings might not be able to fulfil all requirements or may be outside of some criteria, such as minimum setbacks, or access requirements (Penning-Rowsell, 2020). These can also be restrictive in terms of securing finance and insurance (Penning-Rowsell, 2020).

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Opportunities

There are opportunities for utilising all three forms of flood-resilient structures described here in Te Moananui Oceania. Resilient structures against freshwater flooding can enable more effective construction in marginal areas, such as riparian zones, or river floodplains. Existing structures in many parts of Te Moananui Oceania are regularly of lightweight timber construction (Austin, 2001), so there is potential for the elevation of existing structures onto piles or raised foundations to make them more resilient in areas already inhabited and prone to flooding. In peri-urban areas, these strategies mean agriculture and other valuable landscapes could be maintained and enable housing on marginal land. Elevated structures also have other nature-based benefits, such as improved natural ventilation.

Financial case

The cost benefit of flood-resilient structures is not immediately seen. Benefits mostly come after a significant flood event, and relate to reduced costs for clean-up, repair and replacement of structures damaged in floods (English et al., 2018). All three strategies aim to reduce the damaging impact of flood water on the structure. Because each strategy is unique, costs vary significantly depending on many factors, including locality, availability of materials, local expertise, and size.

Floating buildings can vary in cost, from costing between $USD100 – 400 per m2 for a floating adaption strategy retrofitted to an existing building (English et al., 2018), to high-end residential architecture which can cost more than $USD3770 per m2 (Coutts, 2018). Other costs associated with floating buildings include ongoing mooring/lease fees, increased financial and insurance costs, and connection to city services (Penning-Rowsell, 2020).

Elevated construction costs also vary, with a low-cost option including simply elevating an existing building on piles. NIWA (2023) in Aotearoa New Zealand suggests that raising existing timber-framed houses on piles is economic for buildings up to three stories. Some traditional buildings in Te Moananui Oceania are already built using elevated construction, and therefore the knowledge and skill exist locally. Despite this, these buildings require more in material, time, and labour to construct because of the additional foundation height.

Sacrificial ground floors may be the most economic strategy if they are a simple modification of an existing ground floor. This involves rearranging the living spaces in the house to be on higher levels and using water-resistant materials (Cabato et al., 2022). Equally, specifically designed sacrificial ground floors might employ extensive earthworks and more costly water-resistant materials, so have the potential to be expensive compared to other strategies.

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Luxury Tahiti resorts” photograph by Roderick Eime, CC BY-ND 2.0 via Flickr
Amphibious house” floating residential house, diagram from BACA Architects (ASK FOR PERMISSION)
Elevated structure, Kiribati. Photo by Pedersen Zari, 2023.
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Further resources: