> My work-in-progress novel [[Temple Mage|Temple Mage]] was inspired by a documentary I showed my students about Egypt. It touched on the [political crisis](https://click.mailerlite.com/link/c/YT0xNDc5NTQ3MzAxMjE4MjI3MzcyJmM9bTljNiZiPTM4MDg2NTA2NCZkPXYwbDdjNG8=.M1n5IAGZS08yLTSWQbvbLWnmNUyWY3U0OOwaJ5i0gOI) between [[Egypt]] and [[Ethiopia]] over the environmental impact of the Grand Ethiopian Renaissance Dam. > > In [[Temple Mage|Temple Mage]], the dam's creation isn't announced, so I had to figure out what clues would be noticed downstream in a region where flooding is seasonal, since the water level dropping wouldn't happen in a meaningful way. ## Fun Facts - Unstable rivers (i.e. ones that aren't dammed) are [more likely](https://geobites.org/saving-sandbars-in-the-grand-canyon/) 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](https://www.nps.gov/articles/ncpn_flowandveg.htm) and leads to sharp riverbanks instead of smooth floodplains. - Over 2/3rds of the [world's longest rivers have dams](https://www.nationalgeographic.com/environment/article/worlds-free-flowing-rivers-mapped-hydropower); the [one with the most storage capacity is in Zimbabwe](https://www.water-technology.net/features/feature-ten-largest-dams-in-the-world-reservoirs/) 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](http://www.bluefish.org/modammed.htm). - Plankton is more likely to grow [downstream in a dammed river](https://www.researchgate.net/publication/305423341_The_response_of_phytoplankton_and_zooplankton_to_river_damming_in_three_cascading_reservoirs_of_the_Tana_River_Kenya) because the sediments that block light get stuck in the dam's reservoir. - More erosion happens in the deltas of dammed rivers because there's [no sediment to replace](https://www.nature.com/articles/srep14745) what gets washed downstream -- it gets stuck in the dam. ## Flow Volume River flow volumes [impact the reproduction and growth of aquatic species](https://www.americanrivers.org/threats-solutions/restoring-damaged-rivers/how-dams-damage-rivers/) 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](https://chamisa.freeshell.org/dam.htm) by making it significantly colder, which impacts the fish. ## Variable Yields 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](https://www.internationalrivers.org/sites/default/files/attached-files/world_commission_on_dams_final_report.pdf) 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](http://awsassets.panda.org/downloads/wwf_seven_sins_of_dam_building.pdf). ## Dam Fish 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](https://www.watereducation.org/aquapedia/anadromous-fish-restoration). Interestingly, the Nile has few, if any, anadromous fish. It does have the air-breathing lungfish, which requires [special fishing techniques](https://aquafishcrsp.oregonstate.edu/sites/aquafishcrsp.oregonstate.edu/files/09ind07au_prospects_potential_.pdf) 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. ## Impervious Core The [first known dam was a failure](https://watershed.ucdavis.edu/shed/lund/dams/Dam_History_Page/History.htm) so bad that the Egyptians didn't try to dam the Nile for several 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.