Following the November 2016 earthquake, the Hurunui District Council commissioned Kirk Roberts Consulting to undertake an assessment of the extent of cliff instability in the Motunau Beach area.
The council’s Regulatory Committee has today received this report.
The assessment has found that while the November 2016 earthquake sequence has had some short term impact on cliff stability at Motunau Beach, coastal erosion is considered to be the primary cause of long term cliff instability in the area.
The report states that the long-term predicted conservative rate of erosion is 0.8m per year, which remains consistent with predictions prior to the earthquake.
Hurunui District Council’s Regulatory Services Manager, Judith Batchelor, says that while seismic activity increases the likelihood of cliff collapse, coastal erosion (wave action) is considered the primary cause of long-term cliff instability.
“The good news from this report is that the November earthquake sequence has not impacted on the long-term erosion rates predicted for the Motunau Beach area. However, there are still clearly risks posed to coastal properties due to cliff instability.”
“Coastal erosion is hard to predict as the coastline does not erode at the same pace in all places. It is likely to erode more during stormy years and less in other years. This report supports the existing coastal hazard lines which is reassuring,” she said.
One of the recommendations made in the report is that ongoing monitoring of the cliff face and beach area should be maintained. Environment Canterbury is currently looking to improve their existing beach and clifftop monitoring at Motunau using new drone technology.