Salmon runs & water flows
One of the anchor points in the history of the fantasy universe of Verraine was originally inspired by the controversy over the Grand Ethiopian Renaissance Dam, which I learned a bunch about because of a documentary I watched with my students. I wound up doing a lot more research into how dams worked than I expected, which is what originally set me on the path to finding better notetaking software and led me to Obsidian. Given that, I thought it might be fun to revisit that research this week, while I'm visiting my parents in the swampy lands of Georgia (USA) and trying to take things a bit easy since it's supposed to be a vacation.
- Unstable rivers (i.e. ones that aren't dammed) are more likely to have sandbars.
- Stable rivers have more riverbed vegetation like reeds because unstable flows don't scour the roots. This is one of the ways that dams can be bad for rivers, because it reduces diversity and leads to sharp riverbanks instead of smooth floodplains.
- Over 2/3rds of the world's longest rivers have dams; the one with the most storage capacity is in Zimbabwe and although none of the top ten biggest dams are in America as far as I can tell, the Colorado River Basin is the most heavily dammed river in the world.
- Plankton is more likely to grow downstream in a dammed river because the sediments that block light get stuck in the dam's reservoir.
- Conflicts often focus on dams; the Ethiopian v. Egyptian tension is hardly unique. In addition to all the hydroelectric dams that get targeted in times of war, fights over dams are still very common in the Middle East. The Italian city-states battled over water, there's a lot of political tension in the American southwest over water allocation, etc.
- More erosion happens in the deltas of dammed rivers because there's no sediment to replace what gets washed downstream – it gets stuck in the dam.
River flow volumes impact the reproduction and growth of aquatic species the way seasonal temperature variations in the air trigger changes in deciduous trees. They can also lead to weird temperature fluctuations from unusually deep or shallow areas, which can mess with the hormonal triggers in various organisms – including algae, which bloom and block the flow of sunlight to deeper vegetation. And that doesn't even take into account how dams that release from the bottom instead of the top (like modern hydropower dams) significantly disrupt the temperature of the river by making it significantly colder, which impacts the fish.
Dams often underperform their projected agricultural impact evaluation because it's hilariously hard to predict the value of future commodities. My original source for this was this pdf that has since been removed but I might have it in my archive at home if anyone wants. In the mean time, it's alluded to by this report about things that are easy to mess up when building a dam.
Most salmon are "anadromous." They hatch in freshwater, migrate to the ocean, then return to fresh water to reproduce. It's one of the reasons dams are problematic for them, and why salmon runs exist. Interestingly, the Nile has few, if any, anadromous fish. It does have the air-breathing lungfish, which requires special fishing techniques to hunt. It is native to Ethiopian wetlands and inhabits the seasonal wetlands. During the dry season, it lies dormant in the soil after swampy lake beds dry up. It's “hunted” instead of netted like most fish in the Nile. Some folks are trying to get people in Uganda to eat more lungfish because they do better in a world that has to worry about dams and climate change.
The first known dam was a failure so bad that Egyptians didn't try to dam the Nile for thousands of years afterward. The second, however, despite being made of dirt instead of stone, worked well enough. The Mesopotamians built their with a watertight clay core and then covered it with a massive pile of dirt. Probably nothing fancy, but it helped prevent erosion and control floods. This was vital to Mesopotamian civilization's rise and also later its fall, due to excessive salination caused by their irrigation efforts over time.
📗 If you found this interesting, you may also enjoy this past edition about building dams as a fishing technique, or this article about ancient infrastructure, which touches on similarities between fishing weirs and the huge traps ancient hunter-gatherers used to hunt whole herds of gazelles at a time. For a great fantasy novel that uses dams & water rights as a major plot point in the political situation, check out the Imager Portfolio series by L. E. Modesitt, Jr.
💚 If you learned something from this overview, consider forwarding it to a friend and encouraging them to sign up for more overviews of my research into obscure history and science.
🌊 Do you have a favorite story about dams, especially the building of one or impacts of one going up or down? Please reach out — I'd love to hear about it, either via email or in a comment where other readers can see.
Note: There are a couple of affiliate links & codes scattered around, but these always come from links I was already recommending and usually I share them because they benefit you too (i.e. getting you extra time on trials).
Check out one of these related posts
Cloth records, syllabic scripts, and bone calendars.
Antiseptic poop, agricultural poop, & the surprising value of eating poop.
Quick facts about historical cleaning methods from around the world, from lotus leaves to bronze knives.