Those Dunes!

Piha seems to be out of step with the rest of New Zealand, including other parts of Auckland, when it comes to dune conservation.  Council statutory plans, and the Local Board’s own 2018  ‘Great Big Blue Waitakere’publication identify our West Coast dunes as being under threat and needing to be protected with measures to address trampling and human disturbance with fencing and appropriate planting.  Yet the Waitakere Ranges Local Board, Piha R&R and a small group of locals seem to be  hell-bent on opposing effective dune conservation, either on the grounds that planting has altered the surf and caused the beach to widen or on the grounds that some individuals believe that myth, and are upset.

The 2013 Dahm  Management Plan, which is the blueprint for Piha dune management, clearly spells out the natural causes of the dramatic changes we are seeing on the beach with the accumulation of vast amounts of sand moving in from the south.

Recently, a Piha resident (X substituted for his name) put a somewhat abusive post on Facebook that again attacked CoastCare for causing these changes.  An offended member of our community (not the CoastCare Trust) sought a response from Jim Dahm, who was also attacked in the post.  Jim’s response gives an interesting summary of the changes that have taken place over the last 120 years.  His reply follows……

Sand dunes on Whatipu Beach. Photo credit: Dunc Wilson

Sand dunes on Whatipu Beach. Photo credit: Dunc Wilson

Jim Dahm’s response to Piha resident X

X needs to understand and learn to live with nature instead of always wanting to fight and control. This is a wild and very dynamic coastline subject to powerful natural forces. These forces are not going to pay any attention to X and his abusive bluster.

The current trend for seaward advance has been occurring for decades and will likely continue for many more decades. There is a huge pile of sand at Whatipu that has accumulated over the last 100-120 years, and it going to move northwards.

We know (from stories told by local Maori to Percy Smith, which he published in the late 1800s) that this huge plug of sand was once located south of the Manukau entrance. It formed a large sand plain extending right back to the Waikato River entrance (then located where Sunset Beach is now). We also know from hydrographic charts and historic shoreline surveys that this huge plug of sand moved northwards across the Manukau entrance in the 1800s and 1900s, causing significant changes to the channels and banks as it did so. We also know from historic data and current reality that the arrival of this sand built up a huge sand plain at Whatipu in the 1900s, fronting what were sea cliffs as recently as only the 1800s. This sand plain is very similar in nature to that which once existed south of the entrance, as described by local Maori to Percy Smith. And we know from the work of NIWA and others, that large volumes of sand are moving northwards and building Piha and other beaches seaward. In recent years, this sand even appears to have reached as far as Muriwai and the long-standing historic erosion trend there (evident until the last 5-10 years) has now reversed.

I understand the concern with the historic (1991) localised work around the small stream entrance towards the south end, as it seems that was done without adequate consultation and agreement. I largely (though not entirely) concur with Justice Turner’s criticism.

However, any idea that this work was somehow responsible for the development of the dunes at Piha is utter nonsense. Sand dunes are clearly part of the natural beach system at Piha and have formed naturally along the full length of the beach. And at all similar beaches along this coast. There were dunes at the southern end of Piha at the time of the earliest available photos and no doubt earlier. These dunes were seriously damaged by wind erosion associated with poorly managed human use from the 1930s onwards; this is documented with photos in my report. Yes, these dunes have grown seaward as the beach has built seaward, due to sand moving northwards from Whatipu. And that trend of beach and dune advance will likely continue for some time – there is still a lot of sand at Whatipu! All Piha Coastcare have done and all that they ever plan to do, is repair human damage to those natural dunes and restore the natural vegetation that would otherwise exist. The serious wind erosion damage to dunes at the south end of Piha prior to Coastcare is very evident in historic photos. The incredible achievements of the Coastcare team are a credit to them, especially in the face of ongoing bullying and abuse from angry men raging against the tide.

Piha is a wild natural beach on a wild coast and that is its appeal, it is well beyond human control. Those who want to control it (or damage it!) so it will always provide them with surf breaks or views or anything else would be well advised to go somewhere else; unless they want to spend the rest of their lives in futile rage.

Jim Dahm


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