A 2016 Tonkin & Taylor report on the erosion of the banks of the Tamaki Estuary in Wai O Taki Bay suggested a 3-5 m/100 year range rate of retreat. I took some photos in 2013 so wanted to see if the prediction looked right for the last seven years.
My best guess would be about 30cm of loss over the seven year period suggesting the prediction to be about right.
The report suggested a ‘Do nothing’ option which was adopted by the Local Board. The exposed banks are at least 100m long and average about 2m high. If we lost 30cm of bank over the last seven years that’s 60 cubic meters of clay and top soil. Wet excavated clay weighs 1,826 kg/m³, so more than 100 tones of life choking sediment dumped into the Tāmaki Estuary and the Hauraki Gulf (on our watch).
This report has been submitted to the Maungakiekie-Tāmaki Local Board.
Update September 2022. I was invited to present this report to the Local Board a year later. It was well received and has been recorded in their minutes.