For those who may not be conversant with the history Ellerslie Racecourse, along with surrounding areas, has always been on low lying Lava Caves that flood, hence why it was set aside for a Racecourse Reserve/ Domain and not housing etc.
Lake St John, also known as Waiatarua was drained a number of years ago and much of that land is prone to ongoing flood plane issues to this day.
Let commonsense, as they used in Superintendent Robert Graham's era, prevail and leave well alone.
Do remember it was those associated with the wider Retirement / Aged Care industry, including Property Speculators in the 1980's/ 1990's, that failed to factor into account the area where Lake St John was/ is, is prone to flooding what's now called Remuera Gardens Retirement complex a stones throw from Ellerslie Racecourse land.
Information that surfaced subsequent, and prior to, that development would have seen that complex never to have received Consent.
No amount of "Drainage" of the land will ever stop water flowing through underground Lava Caves... as those who live and work in the Ellerslie Region know and understand (Thank you to all those who are now sadly deceased, ( including the wonderful Norm, Trevor, Clarry and Gladys and family who worked alongside Robert Graham and others) and those of you in advancing years who have passed on your Wisdom over the years passed through the generations for your useful insight on our travels)
One to this day knows there's flooding / drainage issues in the area when it rains heavily.
I think we all know about the Healthy Waters Plans and that of Auckland's Water shortages, all of which incidentally have come about through covering up Natural Water Bores/ Springs with concrete..
Note this Report includes diagrams of the area
Drainage of Lake St John / Waiatarua (Report on ) J.B. Thompson, Chief Drainage Engineer 1917
Laid on the Table of the House of Representatives by Leave
https://paperspast.natlib.govt.nz/parliamentary/appendix-to-the-journals-of-the-house-of-representatives/1917/I/999