Right click on each image and select "Open in new tab" - you can then magnify the images.

S12/12/1972 Sourced from http://retrolens.nz and licensed by LINZ CC-BY 3.0
29/09/1977 Sourced from http://retrolens.nz and licensed by LINZ CC-BY 3.0
19/08/1980: Sourced from http://retrolens.nz and licensed by LINZ CC-BY 3.0
Extent of drains: 19/08/1980: Sourced from http://retrolens.nz and licensed by LINZ CC-BY 3.0
Above aerial, with statement from Ray Shine, dated 30 January 2017, who owned Omaranui Station mid 80s to mid 90s: "No extra drains were dug in my time. This aero photo is true to wat (sic) I recore (sic - recall)"