Whaka Īnaka: Causing Whitebait
Designing ecology into coastal infrastructure, from baseline surveys and multi-criteria analysis through to the design of bespoke habitat features, fish passage assessment, consent application support, presentation of expert evidence, and construction advice along 4.4 km of Wellington Harbour shoreline.
2016–2026
context
The Eastern Bays of Te Whanganui-a-Tara/Wellington Harbour, from Point Howard to Eastbourne, have been defended by concrete seawalls and rock revetments for several decades, with coastal defence structures present in some areas since the early 1900s. By the 2010s, many of the existing structures were beyond serviceable life: a patchwork of aging walls that did not provide adequate protection against storm surges and waves, and could not accommodate projected sea level rise. Marine Drive, the only road connecting the Eastern Bays suburbs to the Hutt Valley, was increasingly vulnerable to flooding and closure due to storm surges. In addition, the community had sought a continuous shared path along this shoreline for over 30 years, as there was a lack of connectivity to wider walking and cycling networks. In 2016, Hutt City Council assembled a multidisciplinary team to replace the seawalls, build coastal resilience, and deliver the shared path, a project later gifted the name Tupua Horo Nuku by mana whenua in 2022.
challenge
- Seawalls covered 87% of the 4.4 km project length, but virtually nothing was known about the intertidal ecology of these structures. Before any design decisions could be made, EOS needed to characterise benthic communities across the entire project extent.
- Selecting the optimal seawall type required balancing coastal processes, intertidal and terrestrial ecology, avifauna, landscape, cultural values, urban design, consentability, durability, and cost – a genuinely multi-criteria decision where ecology needed to be integrated alongside engineering and other considerations.
- Translating ecological recommendations into buildable design features – textured concrete surfaces, constructed tide pools, drilled rock pools, colonised rock reuse protocols – required ongoing cross-discipline collaboration to ensure habitat features would not compromise structural integrity or longevity.
- Proposed beach nourishment had the potential to impact on subtidal ecology, but with no existing information on the subtidal area we had to first characterise the subtidal community of the beach areas before we could provide relevant guidance aimed to minimise the potential effects.
- Fourteen piped stream outlets along the 4.4 km project length discharge to Wellington Harbour, several with confirmed or likely populations of banded kōkopu and other diadromous native fish. Seawall extensions, pipe modifications, and proposed beach nourishment all had the potential to impede fish passage, requiring a discrete assessment to identify risks and mitigation for the resource consent application.
our role
EOS Ecology was the coastal ecology lead for Tupua Horo Nuku from inception in 2016 through to completion of the detailed design. Our role spans the full design lifecycle: baseline intertidal and subtidal surveys, baseline intertidal habitat mapping, multi-criteria assessment of seawall designs, fish passage assessment, authoring AEE reports for resource consenting, design of bespoke intertidal habitat enhancement features, expert witness evidence at the consent hearing, and authoring the Seawall and Revetment Habitat Plan to guide the construction phase.
how we approached it
- Undertook comprehensive intertidal and subtidal surveys in 2016 and 2017 across 29 intertidal seawall sites, 31 intertidal beach sites, and 47 subtidal sites – establishing for the first time the ecological values of the Eastern Bays shoreline and nearshore subtidal areas. We ensured our survey methods and data would also be suitable to form the basis of any ‘before’ monitoring dataset to track the long-term ecological success of the project; thereby improving efficiencies and reducing long-term monitoring costs.
- Led the intertidal ecology scoring within the Multi-Criteria Analysis, evaluating eight seawall options across ecology, coastal processes, landscape, cultural values, and cost, contributing to the selection of curved concrete seawalls for 84% of new structures.
- Designed bespoke eco-engineering features – a custom concrete surface texture pattern inspired by local seaweed species (Macrocystis pyrifera and Hormosira banksia), pre-cast constructed tide pools for curved concrete seawalls, drilled rock pools for rock revetments and protocols for salvaging colonised rock from the existing shoreline – and guided use of large pre-cast constructed tide pool units for rock revetments.
- Assessed freshwater fish passage at fourteen piped stream outlets across the project area. including the classification of catchments as ‘confirmed’, ‘possible’, or ‘unlikely’ for fish presence, and the recommendation of site-specific mitigation measures to inform the resource consent conditions.
- Provided advice and guidance around how best to implement beach nourishment without impacting on subtidal ecology.
- Authored key AEE reports on both intertidal and subtidal ecology. The AEE reports were accepted with no Section 92 requests for further information. Presented expert witness evidence at the joint GWRC/HCC hearing, with consent approval following.
- Authored the Seawall and Revetment Habitat Plan (SRHP), a key document consolidating all ecological design specifications as prescriptive, construction-ready guidance so ecological intent is preserved throughout the build.
outcome
Construction commenced August 2022, and progressed bay by bay until completion in April 2026. The value of embedding ecology throughout design was clearly demonstrated by the adaptability of the design during construction: original pre-cast tide pool specifications were adapted on site to pools cast directly into the seawall surface, producing a structurally stronger connection – a change possible because the SRHP gave the construction team sufficient understanding of the ecological requirements. Textured surfaces and tide pools are being rapidly colonised by intertidal biota, with primary succession underway on completed sections. We have submitted a journal article (McMurtrie et al. (2026)) to the NZ Journal of Marine and Freshwater Research as a peer-reviewed account of the cross-disciplinary design process. Our survey data and monitoring methods have also formed the basis for the long-term monitoring of the project, with the first ‘after’ survey of completed structures having taken place in summer 2025/26, providing comparison against pre-construction baseline data collected by EOS before construction commenced.
wider impact
- A nationally significant case study in eco-engineering of coastal defence structures demonstrating how ecological input, integrated from project inception through construction, can enhance the biodiversity value of hard-engineered coastal infrastructure.
- The bespoke seawall texture design demonstrates that eco-engineering features can be integrated into coastal defence structures without compromising engineering performance, visual character, or construction programme. This is directly applicable to the many New Zealand coastal communities facing seawall upgrades under projected sea level rise.
- The first project in Wellington to incorporate textured surfaces and constructed tide pools into seawall design to improve intertidal habitat values. Greater Wellington Regional Council described our work as setting ‘the standard for similar projects where armouring of the shoreline cannot be avoided’ (Dr Megan Oliver, GWRC).
Ecology-led Coastal Infrastructure Design
Coastal communities across Aotearoa New Zealand face the same challenge: aging seawalls that need upgrading to meet climate projections, with the opportunity to enhance ecological values in the process. EOS brings two decades of intertidal ecology expertise and a demonstrated track record of embedding ecological design into coastal defence from concept through construction. If you’re planning seawall upgrades or coastal resilience projects, talk to us about integrating ecology from day one.