Sea level rise will hit hard

A rising sea level is predicted to put many areas in and around Timaru under water over the next century.

A shoreline that pushes deep into the Washdyke industrial estate and puts the port, sewerage ponds and properties around Caroline Bay at risk are some of the dramatic scenarios in reports provided by the Timaru District Council as it seeks residents’ views on how it should approach climate change over the next 10 years.

The council’s draft Long Term Plan, open for public consultation, features three climate change options – do the minimum, do more (preferred) and do even more. The council is proposing a dedicated climate change unit that will cost about $320,000 a year.

According to the specialised reports, most of Timaru’s coastline is at risk.

One report, by Jacobs Engineering Group in July 2020 and commissioned by Environment Canterbury and the council, details the effect sea level rise will have by 2070 and 2120 with different ranges reflecting various magnitudes of sea level rise.

South of Timaru, the railway line will ‘‘most likely be compromised by erosion over a 100-year timeframe under all sea level rise scenarios,’’ with parts of the track compromised in the next 50 years.

The rock wall protecting the Pareora freezing works will also likely need to be maintained to prevent it being compromised, exposing the buildings behind.

Between 2070 and 2120 it is likely the back of the beach by Saltwater Creek will be encroaching on the channel, which ‘‘is likely to impact on the drainage capacity of the channel and ability to continue to use the northern outlet to discharge the creek to the ocean’’.

Erosion at Patiti Point, already causing major problems for buildings and sporting clubs in the area, is predicted to continue, with the report saying by 2120 ‘‘the cliff line is most likely to lie within the current footprint of the cycle track at the south-east corner’’.

South Beach is one of the few places the report says likely won’t see serious erosion, with slightly more sediment accumulating than the amount removed by erosion. The beach is expected to grow slightly over the next 100 years.

Caroline Bay is also expected to grow, but much more significantly. Despite a predicted erosion of around 110 metres by 2120, the beach is expected to accumulate sand by a much higher rate, leading to a net growth at the beach by up to 130m over the next 50 years and up to 290m in the next 100 years.

The report says that at the northern end of Waimataitai Bay, road ends of Richmond St, Climie Tce and Moore St could be affected within 50 years, and ‘‘most likely will be eroded within 100 years without continuation of the protection works’’.

‘‘Only small sections of these roads are likely to be compromised by erosion, and maintenance of the [wall] structure would provide protection in the future.’’

The most dramatic erosion is predicted for the Washdyke Lagoon, which will ‘‘most likely be completely reduced to a wetland within 100 years’’, with the sewerage network and train line affected, and the shoreline lying within the industrial estate at the northern end.

North of Timaru, the wastewater treatment plant and oxidation ponds at Aorangi Rd will ‘‘likely begin to be affected within a 100-year time frame with the back of the beach being projected to be at the edge of the seaward edge of the ponds’’.

The coastal stopbanks that protect Milford Huts are ‘‘most likely to be compromised by erosion within a 50-year period’’. The report says the settlement itself could be affected ‘‘within a 100-year time frame if the banks are not maintained or relocated’’.

Further coast issues are also in a June 2020 report from the National Institute of Water and Atmospheric Research (Niwa), which forecast the increasing reach of damage from strong storm events as sea levels rise.

The report says that the ‘‘significant inundation’’ that can reach up to 1km inland in the low-lying coastal plains north of Timaru, at the moment, could extend to the low-lying area bordering the Rangitata River and Pareora River.

The Timaru port is also listed as at-risk, with waves from an extreme storm event ‘‘expected to overtop the port facility’’.