Geohazard Engineering
Stabilising eroding river banks, coastal cliffs, and riparian bluff faces across New Zealand — working from above to protect waterways and sensitive environments.
New Zealand's rivers and streams are dynamic systems, and the bluffs and banks that define their margins are frequently unstable. Ongoing fluvial erosion at the toe of a slope removes material that is providing passive resistance to slope movement above — leading to progressive instability, bluff retreat and eventual failure. Roads, bridges, farm buildings, utility infrastructure and residential properties located near riverbanks and stream margins face this risk across the country, from the braided rivers of Canterbury to the meandering streams of Northland and Waikato.
Riparian bluff instability is distinct from other forms of slope failure because it involves an ongoing, active process at the base of the slope. Permanent stabilisation requires addressing not just the slope itself, but the erosive mechanism that is driving the instability. Solutions that ignore the toe erosion problem will not provide durable protection regardless of what is done higher on the slope.
APPLICATIONS
GSI NZ CAPABILITY
THE GSI DIFFERENCE
Step 1
We assess the bluff or bank face from above and, where required, via rope access or boat — characterising the failure mechanism, material properties, and erosion drivers. The assessment informs both the engineering design and the consenting strategy.
Step 2
Stabilisation solutions are designed to suit the specific environment, material conditions, and required design life. Typical solutions include soil nail reinforcement using fiberglass nails in corrosive environments, shotcrete or bioengineered surface protection, and drainage where groundwater is a driver.
Step 3
Works are carried out from above wherever possible, with minimal disturbance to the waterway, coastal, or riparian area. Temporary access tracks and site infrastructure are removed on completion, restoring the site to its pre-construction condition.
CASE STUDY
Following Cyclone Gabrielle, GSI NZ was engaged to stabilise a failing cliff face on the Ruamahunga River in the Wairarapa. The site had no road access — the only viable approach was helicopter-supported operations from the cliff crest.
GSI NZ crews manually removed approximately 750 m³ of unstable debris from the face before installing 492 soil nails across three zones using lightweight wagon drill rigs. Shotcrete was applied for surface containment, and biocoir matting was placed across disturbed areas to control erosion while vegetation re-established. All temporary infrastructure was removed on completion, leaving no permanent footprint in the riparian environment.
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492 soil nails and 750 m³ removed, helicopter-only access on the Wairarapa coast.
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2,647 soil nails across 8 slip sites, West Auckland emergency response.
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118 rock anchors and Geobrugg TECCO mesh, helicopter-access stabilisation north of Auckland.
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Riparian erosion left unchecked threatens infrastructure, farmland, and waterways. Our engineers design solutions that hold — engineered for New Zealand conditions.
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