What is a Hydropower Archimedean screw?

One of the early forms of renewable energy generation is the Archimedean Screw. They've been used for thousands of years to move water and other materials from a lower elevation to a higher one. Essentially a screw inside a tube, the Archimedean screw is operated by placing the bottom in the water or material you wish to transport (typically grain, sand, sewage, or even fish) and rotating the screw. The screw picks up material and moves it to the top of the tube. The screw can be powered by anything – in ancient times they were turned by hand or by cattle power, and in more modern times are powered by electricity. 

Just as you can use power to move water up the Archimedean screw, you can reverse the process to generate power by moving water down the screw. The water at the top of the screw moves down, rotating the screw as it travels, and that rotation can generate electricity. This makes Archimedean screws an alternative model for generating hydroelectric power – typically called screw turbines or Archimedean turbines. Though not as popular as traditional hydroelectric installations, Archimedean turbines can operate in rivers with a relatively low flow, and work using a low head (the drop between where the water enters the turbine and where it leaves), making them well suited to smaller installations. They are also widely regarded as friendly to wildlife, as fish can pass through them more safely than through traditional hydroelectric installations.