Dirt Nerd

Mar 23, 2009 19:35

So here's something I've been contemplating. We have all heard/read about how the Nile river floods yearly (or did until the Aswan was built anyhow). And how the annual flood deposited a rich layer of silt on the soils of the Nile valley, fertilizing the fields. How this was so essential to the functioning of Egyptian society and agricultural economy that their entire calendar and yearly cycle of festivals was built around it.

So here's my question. Where was all that silt coming from? Silt is basically soil washing down from somewhere higher up in the watershed. This is naturally occurring in most watersheds but normally in most ecological contexts you would expect it to be more gradual than this. Also, an annual flood that big suggests a lack of water-holding capacity upstream... which is something that you can see as a result of deforestation or destruction of wetlands; also when lands have lost much of their soils already. So it makes me wonder what was going on upstream in the headwaters of the upper Nile. Maybe the upper watershed really was just a naturally barren, erosive country. Maybe it became so erosive during that period because of land use by the Nubians of Sudan. Maybe desertification from the progression of the Sahara was exposing the lands upstream to erosion and contributing to the flooding. An erosion event that big doesn't seem sustainable over the time span of millenia, so it makes me wonder how long it had been happening, and if there was any shift in this pattern over the span of history. And did any of this factor in to the political dynamics between the Nubians and Egyptians over the centuries?

This is the sort of stuff that I get curious about. And why dionysusdevotee calls me a dirt nerd. :)

land, history, environmental

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