Auckland Baptist Tramping Club

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20 walkers turned out for the 10km walk which started at the Horse trek park off Coast Road. The first day the government had allowed groups of 25 to gather. It was good to have the opportunity to reconnect with the wider club members.

Introductions were made on a sunny Saturday morning. The first part of the walk took us to the cell tower with views back towards the south end of Muriwai over the golf course. We then turned north and down the contour to views of Lake Okaihau stopping for a short time. Lake Okaihau- Meaning – Feast of the Winds. The name "Okaihau" name meaning "Feast of the winds", which is relevant to the location of the area on a ridge over 200 m above sea level. Taking the track through the pine forest was an easy dry meandering track back to the Coast Road. Meeting up with the road, the group was able to carry on getting acquainted with friends again after the lockdown.

The easy road walk for about 3km led to a right-hand turn following a horse trail to the dunes that form the length of the playground which is Muriwai beach. Since that Saturday was the first Saturday out of lockdown for groups we walked amongst sunbathers, surfers, swimmers, dogs running free, lead-footed 4x4 drivers, bike’s wheel standing and horse trekkers all with a background of waves racing up and over the black sands which is Muriwai.

We finished the looped walk following the stream back to the car park. Here is an explanation for the rusty water looking stream from Geoff Tremain who comes from an engineering background. He encountered this during my job as an engineer for North Shore City, where the East Coast Bays streams often have iron staining, especially in summer.  It is caused by iron dissolved in the local groundwaters.  Groundwaters are anoxic, and the iron contained in them is in the reduced (Fe2+) form, which is colourless and soluble.  But when it seeps out of the ground and into streams, it is exposed to the air and is oxidised to its Ferric (Fe3+) form, which is brown and insoluble.  It forms a floc of iron hydroxides, which settles to the bottom, or makes the water brown and turbid.  It is most noticeable in summer when the stream flows are reduced, and the iron is not so diluted.   Iron bacteria also feed on the iron deposits, often forming a nasty looking orange-brown ochre slime (see picture).   However, it is completely natural and non-toxic, although stream bed animals and fish do not coexist with it very well if there is too much of it. The same thing sometimes happens with water from bores if the ground is rich in iron.  Once the water meets the air, the brown floc forms, which causes staining and sometimes blockage of pipes.  At Woodhill, the whole area is covered with dunes made of iron sand, so this is where the iron will be coming from in this case.

A great day to be refreshed out of lockdown with great company of people.

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