Water lot we got…

Right. The general consensus seems to be that we’re done with winter now and the good news is that Cape Town’s dams are full to bursting. Not literally though, I hope.

dams

Yes, you read right: our dams are 104.5% full right now, with just Wemmershoek letting the side down with its paltry 99.9%. “Big Boy” Theewaterskloof is looking especially resplendent on 107.5%, no less.
How can this be? Well, it’s not like the water rises above the dam wall and is held there by a giant meniscus or anything (although that would be really cool to see). The extra 7.5% is due to the difference between the intended capacity of the dam and the actual amount of water it can safely hold, as described here:

Man-made dams are artificial catchment areas and, by definition, are storage areas for water. When the dammed water reaches a level that indicates the maximum water that that dam can hold (before being put under stress by additional water pressure), a drum gate opens automatically to prevent over-pressure. The drum gate is designed to keep the dam at the maximum of the storage level – the so-called ‘full’ level – but often the ‘full’ level is well below the dam walls max capacity, for safety. So, as the water level begins to rise, the water level above the ‘full’ level is marked, and typically ends at 10% (or 110% if you like) above ‘full’. At this point, the water pressure is considered to be dangerous and sluices are opened to let water out. These sluices are carefully controlled to make sure that the river below the dam wall does not breach it banks and ruin expensive weekend homes! I think that saying the dam is 107% full is meaningless, and misleading, even though it an engineering necessity.

Either way, despite the fact that we are closing in on 1,000,000,000,000 litres of stored water, it’s still sensible to use it carefully, as the City points out:

It is important to bear in mind that the time to save water is when there is water to save, and we should therefore not become complacent about our water saving efforts. Cape Town will never be in the position of having sufficient water to waste, and we must continue to be vigilant.

Right you are. Not that my garden will need any more watering for about a month given the last couple of weeks.

More water

If you have been in or around the Western Cape over the past couple of weeks, you can’t have missed the rain we’ve been having. It’s caused floods, landslides, death and misery. However, on the bright side, it has also filled up our dams nicely.

Hoorah!

But it was only when I read the City’s weekly dam level figures, published each and every Monday, that I realised just how much it had filled up our 6 local dams.

It’s the last two columns you want to look at – this week versus last week – indicating that the percentage storage in our dams has increased by 7.7% in just 7 days. That’s good news, as we need the water for our long dry summer (remember that?).

7.7% is quite a lot, incidentally. I’ve been doing some rudimentary calculations (while fuelled by Diemersfontein pinotage) and it appears to me that we have almost 69 billion more litres stored than we had this time last week. 68,609,000,000 litres to be exact.
That’s enough to fill 27,443 Olympic size swimming pools, although if you were to actually do that, I wouldn’t be allowed to water my garden in February.

So don’t.