Firstly, I apologise for being a little slow on the uptake to understand and convey this, but I had to wade through talk about Hectare equivalents, 100-year security of supply, environmental flows etc. However, I now believe that I understand how the dam allocations work (or don’t work).

Who Owns The Water Behind The Waimea Dam?

From all the pretty graphics and charts, you may be under the impression, as I was, that the dam reservoir holds water capacity in three allocations; as apportioned to irrigators, environmental flow, and urban supply. And you might assume that each party owns its share of the water occupying the allocated storage capacity.

You might have been right with that assumption had there been three pipes exiting the dam. If the irrigators had a pipe that we could meter then we could shut them off when they consumed their allocation, and when the fish drank their water from the environmental flow pipe we could shut them off, and council could manage the share allocated to urban water supply via another pipe. In this scenario, the allocation percentage might make sense.

But. . . that is not the scenario that we have on the table. In the current scenario, all of the water stored behind the dam belongs to one party. Believe it or not, the fish own all the water.
Let me explain.

Because we only have one tap on the dam, and it feeds directly into the river, the only measure of control that we have is the river flow level. When the river level drops to a point that the fish dictate is unhealthy (or slightly before) we start to release water in the dam. We continue to release water from the dam in quantities that maintain happy fish until such point as there is no water left in the dam (other than a minimum level that we are required to retain), or until such time as the natural flows increase to a point where we can stop releasing from the dam.

At the point where the dam runs dry, if the drought has not broken, the fish will be unhappily flapping their fins on a hot dry river bed, the irrigators will have prunes not apples (I know apples don’t turn to prunes but you get the equivalent idea) and desperate urban supply water users will be standing on street corners in the dark of night buying bootleg water from smugglers bringing water across electorate lines. Armageddon reigns as described in the no dam scenario headlines. Fortunately, these events only occur in a greater than 1 in 60 year drought event. Although global warming proponents may find this a slightly more alarming statistic.

What all that means is that in this broken model for a dam, it doesn’t matter how many hectare equivalents council urban water club signs up for (whether one or one hundred thousand) the result is the same. Just as it doesn’t matter how many hectares the irrigators sign up for, which is probably why they over sold the need initially and then drastically reduced their intended subscription when it came to apportioning costs. In other words, the more dam debt council assumes does not translate to greater security of supply to urban water users.

Remember the fish own the water and dictate when supply is turned on, how much flow is required, and for how long the flow runs until the dam is drained (if required). The irrigators who are next in line, because their pumps are positioned above the urban water take at the mouth of the river, will use their over-allocated consents to legally pump until their hearts are content (or their permit allows). They will continue to pump while water flows down the river from the dam at a level that keeps the fish happy further exacerbating the need to release more water to keep the fish happy, until the dam runs dry. There is no mechanism to stop them pumping once their “share” of the dam reservoir is empty – and why should they, because they have a dam to pay for, and the fish will drink all the water anyway if they don’t use their share.

To top it all off, while the fish are happy drinking and the irrigators are happy pumping, the urban water users will also continue washing their cars and watering their lawns until the day that the dam runs dry.  There is no incentive for urban users to cut back on water use because the dam they paid for will be releasing water to feed the irrigators (who won’t cut back) and the thirsty fish who likewise need to maintain their share flowing into the sea (we don’t want the rising sea levels to run dry after all).

So you see, it doesn’t matter who pays for what share of the dam, the fish own the water and while they are happy everyone else can use as much as they please (or are daily consented to take). That is why this model is broken. There is no incentive for anyone to conserve water at any point before the dam runs dry.

If, on the other hand, we were to look at a “plan B” option, such as the water reservoirs built on the side of the river for urban supply, then we have a different model. Water use would continue as normal until the fish said cut back. At that point, the irrigators would have to start cutting back to maintain river flows and happy fish, and urban water users would have to either start cutting back and/or start supplementing their supply from the reservoir. In this scenario, there would be an incentive for urban supply users to start reducing their demand because they only have a finite supply in store once the river drops to minimum flow.

The bonus with this model is that there is a finite supply available for urban water users that the fish cannot drink and the irrigators cannot get their pumps into. What urban suppliers pay for urban suppliers get exclusive use of. This is a security of supply model as the reservoirs can be as big as money will allow and need drives.

I am not advocating the “Plan B” as a more cost-effective model, or to have the same benefit to the fish (as clearly there is none), but it does have some merit when it comes to ensuring a security of supply. It also has the advantage of being more likely to be constructed to the P95 (95% certain it can be built on budget) than the dam scenario – but that is fodder for another post.

This post is just to help you understand what your money spent on a dam will get you, and how happy you will make the fish.