Coastal erosion cause for concern
A small South Canterbury river mouth settlement is under threat with coastal erosion shrinking the lagoon that protects the community.
Environment Canterbury South Canterbury natural hazards team member Chris Fauth spoke about coastal erosion areas at the Timaru District Council’s environmental services meeting last week with a heavy focus on the Milford Huts. The Milford Huts is a small river mouth settlement located at the Ō pihi River mouth, seven kilometres south of Temuka.
‘‘We obviously have a couple of major hut communities right out the coast, the South Rangitata and the Milford. They’re affected by a range of coastal issues at varying degrees,’’ Fauth said.
‘‘It [South Rangitata] has its issues, it is prone to coastal inundation, there is erosion there, they have issues with flooding when the mouth becomes blocked.
‘‘Generally speaking this one here is somewhat less vulnerable than the Milford Huts.’’
Fauth said on average two metres of land is being lost to erosion a year in South Canterbury, which is also shrinking the lagoon protecting the Milford Huts. ‘‘As the lagoon reduces in size the buffering effect it has in terms of protecting it from the sea is obviously reducing as well.’’
He said the lagoon had got so small it could be one tide cycle between ‘‘things looking okay’’ and then the lagoon was high enough to be a threat.
Erosion at Timaru’s Patiti Point was the feature of a University of Canterbury study in 2020 which revealed accelerated erosion over a three-year period.
The erosion forced the South Canterbury Deerstalkers’ Association to move its building to a safer spot. Fauth also said the Milford lagoon was in a dire situation as because of land use practises, the lagoons where unable to shift, which is what would have happened before, naturally.
‘‘So they [the huts] are kind of getting squeezed in on both sides, and the future without any sort of change in the practise of what we do now is that they’ll just be lost [the huts],’’ he said.
‘‘If [the waves] get over the beach and the lagoon’s full, they can continue through without really breaking, and then they’ll start breaking on the coastal bank which is right up hard against the huts and that puts that bank at a real risk of being breached.
‘‘And should a breach occur then you’re looking at quite a dangerous situation for anyone in that community.’’
With the shrinking lagoon and the erosion issue, things for the community could change within one tide cycle, he said.
‘‘What will become difficult is when, you know we’re heading that way [losing the settlement], it’s harder and harder to give good warning, and that’s what I’m talking about those tidal cycles, particularly like from the river, because they are also prone to river flooding, you generally have some time,’’ he said.
Fauth said the lagoon could be half full in the evening, and then a quick change of sea conditions could fill the lagoon overnight.
‘‘And that situation is only just going to worsen through time, so it’s a real one for the future – what to do with this community and how to protect it.’’
The presentation from Environment
Canterbury also included coastal erosion points at the South Rangitata Huts, Ō rari River Mouth, Horseshoe Bend Lagoon, Waitarokao/Washdyke and a railway line south of Timaru.
The potential dangers at Timaru’s Redruth if Saltwater Creek floods was also mentioned.
‘‘Some communities particularly at Milford, and to a lesser extent South Rangitata Huts, will become increasingly vulnerable to pressure resulting from coastal hazards. [It is] inevitable that these will need to be addressed,’’ he said.
Environment Canterbury and Timaru District Council officers will continue to work with landowners on coastal areas about how to manage coastal erosion and re-establish stop banks, as private landowners are responsible for maintaining stop banks.