Auckland Council’s $1.87 Billion Stormwater Deception : How Bad Math could Lead to a Bad Decision

💢 ❓ 👀 💰 Auckland Council’s $1.87 Billion Stormwater Deception : How Bad Math could Lead to a Bad Decision 💢 ❓ 👀 💰

Council is scoping out gold plated, diamond studded, underground detention tanks and telling our elected councillors that the cost of doing this in Glen Innes / Pt England / Panmure area is $2 billion.

I say this is ❗BALONEY❗

Council quoted $2 billion for private developer option versus the council option at $780 million and that 78,600 tanks are needed at 1 tank per 100 m².

This is MISINFORMATION

Here is why:

💧 786 hectares of developable area (conservative at 80%) of which council says 45% is currently impervious. They use a 10 year storm temperature of 2.1 deg C and static estimate method.

Council says this costs $2 billion but standard NZ engineers says council has ‘forgotten’ to adjust for the current houses that are already there — the land is not bare.

💧 So the cost becomes $868 million (using my estimations)

Council says the total impervious area at full build out will be 90%, planners say NO because it is not allowed and Council is using INCORRECT methods to calculate actual impervious area. I will use 70% and assume that council will check the planning rules and legislated monitoring rules.

💧 So the cost becomes $482 million (using my estimations)

Council says the tanks are to be underground, cost $4,650 to supply, and $19,952 to install (these figures are quoted to have come from Alta Consulting NZ). Many developers say the costs are between $2,000 and $6,500 and above ground slim-line tanks are easier and better (I have quotes and so do many others)

💧 So the cost becomes $49 to $130 or $262 million (let us say $130 million)

When I received the official document (LGOIMA), my eyes went directly to the 786 hectares needing 78,600 tanks — I could not believe this would be so wrong and pass through checks.

I asked council to confirm that actual engineer’s had prepared the work and checked it: two have, engineers, one more junior than another both of which are well qualified.

Auckland Council, how to explain presenting such figures to the constituents and potentially influencing their decisions with $2 billion v $130 million?

Some of the Councillors on 5 March didn’t want it to go to discussion!

A key executive reinforced the high cost of $2 billion, then presented a hybrid solution that dropped the council spend to $472 million — this only accentuated the differential.

What the BEST CHOICE is: the council in-ground option or the developer option? Giving out ERRONEOUS INFORMATION may harm decision making. The council solution really the best? Don’t create financial bias.

Please check with Alta Consulting NZ for appropriate cost estimates.

Please recheck your numbers.

Note: we all appreciate the rapid and thorough response to our information requests, that is not unnoticed.