No flooding here…

At the risk of sounding like a cracked record, I note that once again, summer urban flooding makes the newspaper, when not a drop of runoff has left our property during or after this afternoon’s intense downpour.  Our tank is now a bit over half-full, and the two raingardens remain close to empty, with plenty of capacity to absorb any more storms that are coming tonight.

In oddly related news, earlier this week, the state government spruiked the new permanent minimum annual water order from the Wonthaggi desalination plant, as meaning “better water security for Melbourne and better plant management”.

Funny story, the need for ‘better plant management’ line.  The government placed their first order from the plant for 50 gigalitres last year when the dams briefly fell below 60% full (leaving us with a paltry five-years of water supply in our dams, to which the desal order would add about a month’s supply).  Trouble is, they couldn’t manage to turn the plant on, it having been in maintenance mode for four years.  They had to bring in a convoy of diesel generators to get it going (so much for the long-forgotten promises that the plant will be carbon-neutral), and having started delivering the ordered water the other day, the deadline for them to deliver the 50 gigalitres will be tight.

But that’s neither here nor there: let’s look at the economics of this water order. Four years in, the government have ordered 50 gigalitres, with a new, ongoing commitment of 15 gigalitres per year (~0.8% of the storage capacity of Melbourne’s water supply reservoirs) from now on.  That means about 15 gigalitres/year since the day the plant officially became operational.  The cost of the desal plant to Victorian taxpayers has been reported as $620 million per year (this has probably changed since they varied the contract to extend the period of payment, but it is indicative, and doesn’t include the additional costs of the first 50 gigalitre order, or pumping costs to get the water to Cardinia Reservoir).  15 gigalitres at $620 million dollars = $41 per kilolitre, a long way from the $2–3 per kilolitres that desal proponents have claimed.

So what has the desal plant got going for it?  It provides us with some water at $41 per kilolitre, burning large volumes of diesel thereby creating a lot of carbon emissions in the process. And it reduces the incentives for the people of Melbourne to use more sustainable sources of water that could more effectively increase the security of our large network of reservoirs, while improving the liveability of our city and the health of our rivers and bays.

Here’s a go at a similar economic assessment of our stormwater retention system.  At most, it is costing us $380 per year in interest payments (at most the system added $8,000 to the cost our renovations; energy costs are negligible – our renovated house is using about 50% of the electricity that it used to use).  It is providing us with ~44 kilolitres of water each year = $8.60 per kilolitre: already looking like a clear winner compared to water from Wonthaggi. But any balanced assessment needs to also factor in the other costs and benefits provided by any water source.  Our system provides several community and private benefits that need to be discounted from the (already relatively cheap) cost per kilolitre:

  1. Contribution to urban flood mitigation
  2. Urban cooling
  3. Urban food production (our raingardens require near-zero maintenance)
  4. Protection of rivers and bays

All of these must reduce the (real, community) cost of $8.60 kilolitre of our system.  In contrast, the reduced incentives for Melbournians to pursue these benefits on their own properties, the increased carbon emissions and the additional pumping costs, add to the $41 per kilolitre for desal water.  And yet, government departments continue to struggle to make an economic case for stormwater management that will truly protect our waterways and bays….

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