July 2019
The Regional Hazards team at Waikato Regional Council have developed an inundation model to better understand the extent and implications of coastal inundation that might occur in future as result of sea level rise and increased storm events.
The results of this modelling were spatially overlain with current and projected future land use result from WISE.
Analysis Undertaken:
Inundation layers for a range of Reduced Levels (18000 – 5000 mm in 200 mm increments) were modelled to represent a range of possible outcomes from future sea level rise and storm surge events.
The extent and location of land use in Hauraki basin impacted by these levels were assessed both at 2013 and at end of WISE Reference scenario (2064).
The distinction is made between areas that are ‘inundated’ (land is below the Reduced Level [RL] and directly connected to sea – i.e. would require additional stop bank / flood protection infrastructure to maintain land use) and ‘saturated’ (land is at or below the RL and NOT directly connected to sea – i.e. would require drainage infrastructure to maintain land use).
Assessment of extent of inundation impact on infrastructure (Roads) and regional economic activity (Value Add) were also made.
Key Findings:
As water levels increase the area of land use impacted increases from 22,500ha at 1800 mm to 58,400ha at 5000 mm.
Scale of land area potentially impacted by increasing sea level
Under the WISE Reference scenario there is minimal change in the rural land use types in the inundated area. There is some urban land use change around key settlements in line with projected economic growth and population change.
The key ‘tipping point’ for extensive inundation is when existing flood protection infrastructure is exceeded. This analysis assumes that only the current level of flood protection is provided in future.
Dairying is the major land use in the inundated areas (with ~18,800 ha impacted at 1800 mm and ~44,000 ha impacted at 5000 mm). Sheep and beef is the next largest land use impact by area (with ~2,300 ha impacted at 1800 mm and ~5,000 ha impacted at 5000 mm). The regional economic of these area if they became unusable for current land use (and assuming they would not relocated to other parts of region) would for Dairying be 5.4% of regional Value Add at 3000 mm and 6.8% at 5000 mm. For sheep and beef it is significantly less (0.65% of regional Value Add at 3000 mm and 0.78% at 5000 mm).
Impact on urban land uses is smaller in special extent but significant in terms of potential disruption and community cost. Potential impact of projected 2060 land use include:
| Land use (at 2060) | Area impacted at 3000 mm (ha) | Area impacted at 3600 mm (ha) | Area impacted at 5000 mm (ha) |
| Lifestyle | 415 | 472 | 569 |
| Low Density Residential | 126 | 157 | 231 |
| Commercial | 49 | 50 | 64 |
| Manufacturing | 65 | 82 | 119 |
| Community Services | 70 | 90 | 115 |
| Airport | 30 | 30 | 30 |
Most of this urban land use impact occurs in the Thames area, Ngatea and Kerepehi, with issues emerging in parts of Paeroa at the highest levels
The economic impact on urban land uses is not available directly from WISE outputs, but would be considered significant and should be part of any further assessment.
The extent of inundation impact on the Road network is 150km at 1800 mm up to 440km at 5000 mm.
View the Full Report >> (15mb)
Next Steps:
The real power of WISE as a scenario tool would come from modelling possible adaptation strategies. WISE could model a number of adaptation strategies to help better understand the requirements and options for more resilient land use in these areas.