WHY IT MATTERS
EXTREME RAINFALL HAS ALREADY OCCURRED
On an 800m² property, 300mm rainfall equals: 240,000 litres ≈ 7 shipping containers of water
Where did it all go?
- About a third will have collected and been redirected into legal stormwater drains.
- The rest will have flowed over lawns and gardens - or infiltrated the soil.
- Some will have flowed to the roadside.
- Some will have flowed over neighbouring properties.
- The process goes on unnoticed
- The effects are real.
This scale of rainfall is not theoretical. It has already occurred.
- During the January 2026 storm event, lives were lost in the wider region.
- Extreme rainfall can carry fatal consequences.
Reducing landslide risk is a practical responsibility.
HOW WATER BEHAVES DURING HEAVY RAIN
Two different but related processes
occur during intense rainfall:
- Flooding occurs when rainfall intensity exceeds the ground’s ability to absorb water.
- Water flows across surfaces and accumulates as it flows downhill.
Slope stability decreases when excessive infiltration raises soil moisture. As moisture builds, soil strength reduces ; soil weight increases.
Some natural infiltration is necessary for plant life and seasonal cycles.
However, during heavy rainfall:
- Ponding
- Prolonged saturation
- Concentrated subsurface injection (soak holes)
- Scouring and erosion
All increase risk.
In intense events, water should move efficiently to lawful drainage systems rather than linger on and in the ground.
CUMULATIVE MOISTURE MATTERS
Traditionally:
- Summer dries slopes
- Winter restores moisture
But when summers are wetter, slopes may enter winter already carrying elevated moisture levels.
Each additional storm compounds
the soil moisture loading. Landslide risk increases.
STRUCTURES
ARE
LINKED
Retaining walls hold soil. They do not remove water.
Rainfall above or behind a retaining wall drains through to the base, or runs over the top.
Retaining wall drains only run when the retained soil is already wet and heavily loaded
Some retaining walls depend on lower slopes or lower walls for support.
If lower ground weakens due to saturation, then linked structures may lose stability.
Water links properties.
WHY
ACT
NOW?
- Insurance markets respond to frequency and severity trends.
- Buyer confidence is influenced by perceived long-term stability.
- Maintaining physical resilience supports economic resilience.
Being “rain ready” is about understanding water behaviour before the next extreme event.
SLOPES ARE INTER-CONNECTED
- On sloping land, rainfall does not remain within property boundaries.
- Surface runoff and below-ground water links neighbouring properties.
- Managing water responsibly on one property reduces risk for those below — and also for those above.
- Rain Ready Omokoroa recognises that slope stability is shared.
Shared slopes require shared responsibility.
