On successive days (21, 22.1.26) the Otago Daily Times ran stories describing unusual markings on roads and pavements that have turned out to be associated with potential Dunedin City Council plans to upgrade the Forbury Rd stormwater drain (sometimes euphemistically referred to as an aqueduct) that nowadays struggles to fully intercept runoff from the St Clair hills during heavy rainfalls to the detriment of some streets in a corner of South Dunedin.
This is primarily a consequence of urban development in the more fashionable hill suburb over recent decades.
The initial slightly quirky article, somewhat facetiously but nevertheless accurately, referenced DCC’s "chequered history" in respect of South Dunedin flooding issues. The second article has raised serious concerns.
In January 2025 the council opted to adopt what it chose to call its three short-term alleviations (I have referred to them here as "STAs") to mitigate flooding.
There were highly optimistic but doubtful claims of their benefit.
STA 1 involves upgrading the pipe described above. The concept at least has merit but is years overdue. A year after the work was finally approved, we are now told that survey work has yet to be completed.
The second newspaper article also revealed DCC’s view that STA 2, a new pump setup in the Hillside Rd/Orari St area, is "complex" and that construction is "likely to be a number of years away yet".
That is not short-term alleviation; it’s a continuation of long-term neglect.
STA 3 is the smallest, involving the installation of a relatively short pipe from the Andersons Bay Rd area to the pump station.
Councillors were told at their January 2025 meeting that the project had its genesis nearly 15 years of inaction ago in the often-referenced report South Dunedin Integrated Management Plan (Opus/URS 2011). They were told that that report indicated the pipework would achieve a 13% reduction in flooding across the catchment.
This outcome would seem highly optimistic considering the number of "bottlenecks" known across the long-neglected drainage system. Despite this, it would appear that no-one checked out the report’s detail.
It turns out that the 13% figure was derived via a "preliminary" simplistic one-dimensional modelling process.
When Opus/URS ran a more accurate two-dimensional model they reported that "reduction in predicted property flooding was almost imperceptible".
This was clear for all to read on page 177 of the report. Are we to assume that no-one at DCC bothered with the detail? Or is there another explanation?
To summarise, one of DCC’s three short-term alleviation projects is reportedly years away, one reportedly achieves imperceptible benefit and the third might get started sometime next year. That will be 12 years after the 2015 flood.
Contrary to this reality, ODT readers were told (3.10.25), on the first anniversary of the latest flood debacle, that the works would "make a huge difference to South Dunedin", and that "in three years’ time the situation will be different".
It is to be hoped that the newly elected council will urgently reverse this ongoing avoidance of reality and prioritise urgently needed comprehensive solutions along the lines of those recommended by their own consultants in 2017.
Perhaps South Dunedinites should take a leaf from the book of Surrey St residents and refuse to continue to be treated as second-class citizens by City Hall.
— Retired engineer Neil Johnstone is an associate of the Surrey St Flood Action Group.
