Horizons Regional Council, in collaboration with Wanganui District Council, has recently finished maintenance work on South Spit in order to strengthen existing erosion control downstream of Wanganui Airport.
Horizons group manager operations Allan Cook says works comprised of extending and strengthening a number of existing permeable piled groynes, which are wooden structures that help control river alignment.
“River flow had progressively been eroding the sand dune beyond the old groynes, thereby reducing their effectiveness. We’ve used almost a thousand tonnes of rock, carted in from Waitahinga, to extend the groynes and thereby protect the spit,” says Mr Cook.
“We’ve also repaired approximately 100 metres of the hardwood ‘walings’ on the existing groynes which have been in place since the mid 1950’s. Those structures have performed very well over the years, and given the huge amount of flood-borne debris they have collected and shed, they have required surprisingly little repair work.”
Mr Cook says it’s crucial to maintain the various structures that have been designed to protect the South Spit.
“We need to maintain the present alignment of the river downstream of Landguard Bluff and ensure it continues to flow out to sea through the moles. A recurrence of the South Spit breach that occurred in the late 1940’s would seriously impact on recreational and commercial use of the river and its harbour and could compromise flood protection at Balgownie,” he says.
The work was completed by local contractors ID Loader Ltd and took approximately 5 weeks.