## Tuesday 21 August 2018

### A simple landfill calculation

That this one comes up so often speaks poorly of our basic numeracy and sense of scale. There's basically no chance that landfills expand to take up any substantial part of the country.

This is the kind of back-of-the-envelope thing that everybody should be able to do in their head.

Kate Valley services Christchurch. It has 1000 hectares total, only a tiny part (37 hectares) of which is actual landfill - the rest is forest buffer and the like. But let's call it 1000 hectares. It has a 35 year life expectancy. The Christchurch area is about half a million people. Let's keep all the numbers round to make life easier - we're looking for order of magnitude stuff here really.

If Kate Valley can handle 500,000 people's trash in a 1000 hectares for 35 years, then it could handle a million people's rubbish for 17.5 years. A thousand hectares divided by 17.5 is about 57 hectares per year per million population.

Let's be conservative and round that on up to a hundred hectares per million population per year. It makes the numbers easier. I'm pretty sure that Kate Valley covers the whole Canterbury region of about 600,000 people, so I should be rounding down instead. But it really isn't going to matter, and I can't be bothered to check fiddly details.

New Zealand's land area is about 26 million hectares. Let's restrict ourselves to agricultural, non-arable land. Basically land that isn't in crop but can be accessed. There's about 10 million hectares of agricultural, non-arable land. I ruled out arable land because it's more expensive and y'all have some kind of potato fetish that if anybody proposes doing anything on ground that could be growing potatoes, your heads explode because importing potatoes is somehow worse than importing anything else. So we won't include that land in the calculations. Pukekohe is safe. But I'd expect there's a pile of other land that could be used that I'm not including too. 10 million hectares is a nice round number for easy order-of-magnitude calculations.

Let's suppose that New Zealand's population doubled to 10 million people. Those ten million people would be using a thousand hectares per year. That's another easy round number.

There are a thousand thousands in a million, and ten million hectares to play with, so it would take about ten thousand years to use up all of the non-arable agricultural land for landfill. Those are numbers big enough that it's impossible for errors in my rough figures above to much matter. If the use rate is double what I'd put up, then it's 5,000 years instead of 10,000 years.

"But we'll run out of land!" arguments never have an appropriate sense of scale. Nor do they ever have any appreciation of basic economics. If scarcity did start biting, land prices would bid up. In the landfill case, that would mean tip fees would go up - and markets would do their usual thing. So don't come away from this with the dumb-take that Crampton figures that all the paddocks should turn into landfills. I'm pointing out rather that land is far from scarce and putting some ballpark numbers on it for a sense of scale. And if land ever started becoming scarce, the price system already deals with scarcity.

Addendum: I've switched to screencaps from Twitter's embed code because too many folks have started nuking their accounts and making my old posts that embed them look like bomb sites.

#### 1 comment:

1. Also, land fill isn't wasted land.

A number of landfills have become parks, or especially sports fields. There's a nice one in north Hamilton.

You take a fairly useless gully and smooth it flat. You end up increasing land!

A fair chunk of Manhattan is recovered from the sea this way.