Wednesday, 15 August 2018

WHITIANGA WEATHER

Coastal erosion to be considered in new Shoreline Management Plan

The storm on Sunday 15 July, coupled with a set of king tides, caused significant damage to the Mercury Bay coastline. The Captain Cook memorial in Cooks Beach toppled into the water, the erosion at Flaxmill Bay, already threatening Purangi Road, worsened and some of the dune plantings at Buffalo Beach in Whitianga washed away.

Coastal erosion has been a problem in Mercury Bay for the past four decades. Climate change, a variety of development activities and the ocean’s natural cycles are all being considered as possible causes of the erosion. These possible causes will be explored in a Thames Coromandel District Council Shoreline Management Plan (SMP) that will be developed over the next three years. The SMP will part of TCDC’s Coastal Management Strategy that was adopted on 27 June.

Development of the SMP is the responsibility of Jan van de Vliet, TCDC’s newly appointed coastal engineer. “The purpose of the SMP is to look at all of the Coromandel’s coastline and work out what can reasonably can be done to counter the effects of erosion and inundation while working with nature as much as possible,” he says. “Everything really is on the table, from the increased use of soft options like sand push-ups and dune plantings to groynes, rock walls and other hard structures.

“The plan will also consider the possible boundaries of the ocean’s natural cycles, in essence forecasting when and where erosion will stop and beach build-up will start to occur again. We won’t be considering pockets of coastline in isolation. The reason is because it’s simply not possible to implement a solution in one area without effecting some changes in another area.”

Jan says in addition to Mercury Bay, the west coast of the Coromandel Peninsula is at the moment a coastal erosion hotspot. “While we’re working on the SMP, we’ll continue with soft options to protect the coastline, but where certain trigger points are reached, we’ll have to consider hard or managed retreat options,” he says. “The most obvious trigger points for hard options will be where infrastructure like roads is in danger. The hard options we’ll look at include, among others, rock walls and backstop walls.

“There are already some soft options in place in parts of Mercury Bay and we’re monitoring those to see how they hold up. It’s important to work with nature where possible and let’s not forget that hard options are very expensive and don’t look pretty.

“Backstop walls are a hard option we’ll consider much more carefully. A backstop wall sits behind the dunes and the sand can rebuild in front of it. It’s a way to recreate dune frontage while still having something in place to stop the erosion.”

Allan Tiplady, TCDC Area Manager North, says that the dune planting programmes that are currently in place will continue. “Despite the fact that some of the dune plantings along Buffalo Beach have been taken away by the waves in the storm of 15 July, we firmly believe that well-established dune vegetation is a viable solution to coastal erosion,” he says.

“The dunes plantings that have washed away at Buffalo Beach, next to the existing rock wall and in front of the Mercury Bay Boating Club, were all relatively new plantings. The plantings that were done four and five years ago, closer to the Taputapuatea spit held up well in the storm.

“We will have a planting day at the Taputapuatea Spit at the end of August.”

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The Mercury Bay Informer is a highly popular community newspaper, based in Whitianga. The paper is distributed throughout the Coromandel Peninsula, coast to coast from Thames to north of Colville.