9 Jan 2012

The Nilometer

BH suggested that I check out the Nilometer when I was in Cairo, and I did. It's an interesting measuring device that would record the highest level of the Nile as it flooded (the center pillar is marked). That level was used to determine the tax rate on farmers, with higher waters attracting a higher rate and lower waters (with potential for a food shortage) leading to zero taxes.

The Nilometer has not been used since Aswan High Dam (AHD) went into service in 1970, ending flood cycles that had occurred for millennia. Floods damaged property, but they also renewed the fertility of fields, built up the Nile Delta, and flushed water ways for the benefit of aquatic life. Fertility and Delta health are not now declining.

It's my impression that it will make more sense to breach AHD in the future, as the losses from evaporation behind the dam, siltation and lower fertility start to become more expensive relative to the benefits of reliable irrigation. There's a lot of hard infrastructure in the way of normal flooding, but most of it can probably be set back.

Aquadoc also has an interesting post on how higher groundwater levels associated with AHD are damaging buildings near the Nile.

Bottom Line: There are costs to blocking a river above and beyond the cost of concrete.

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