Ian and Rob have been tracking down some history of the Williamson pond.
 
This is the approximate dateline:

1944 no evidence of any stream or erosion - just normal part of sand dunes and coastal lines. This is pre-settlement times.
 
1974 – Williamson Road pipes laid and extended through what is Ocean Road across the park and through the coastline.
1985 – Coastline was scouring badly so pipes were cut back to where they are today, a hole was dug and with that sand the large dune to the left (closer to the Surf club) was formed. The discharge in storms would fill the hole and be retained by the hill in the dunes and then soak out through the sand.
1997 – a little vague but after Bola the hill was partly washed away and scoured back to the pipe discharge. The Vee was formed. To overcome this a weir was built
2017 – after these floods the weir had been damaged so a second one was built back 3m and higher. Sometime later the swale to the section beside the last house on Seaview was formed to stop King tide surges rushing over the top. Apparently logs got washed onto the grass. Steve from Viola says. Pipes from Williamson under Ocean and to the concrete were upgraded in diameter – we understand in readiness for the current proposed upgrade of pipes down Williamson.
 
Pre settlement the image shows us little coastline scouring and no stream. (1944 image as shown)
 

That is the history as far as we have got.

1944 photo before Causeway and before sedimentation.
 

2023 Moanu Anu Anu now the dark side of Whangamata

This extract from P13 Environment Waikato 2008/12 Coastal sedimentation paper
Whangamata Harbour
• Whangamata Harbour catchment contains 43 per cent plantation forest, 30 per cent
native forest and 11 per cent pasture.
• The most recent estuary sediment core study estimated that pre-European
settlement sedimentation rates were between 0.10 and 0.18 mm/year in
Whangamata Harbour. From the 1940s until the 1990s the average sedimentation
rate was estimated at 5 mm/year but may have been as high as 15 mm/year in
some areas of the estuary, such as near the Moanaanuanu Causeway.
• A rapid expansion of mangroves and a decrease in seagrass has been observed
around the same time as the rise in sedimentation rates. Mangrove coverage has
tripled and seagrass almost halved over the last 50 years.
• The estimate for sediment yield from the Hicks and Shankar model (5048
tonnes/year – for the entire 52km2 catchment) is much lower than the estimate for
sediment deposition (14,622 tonnes/year – for just a 22km2 sub-catchment). The
sediment deposited in the estuary has been identified as catchment derived