> Blocking water with a dam is a well understood problem
I feel like we still have some problems with dam building, because they keep failing. We struggle to get the building material (in particular, sand). Concrete is pretty awful in terms of CO2. Dams of all sizes cause problematic changes to the rivers they're on, and block flows of fish and other animals. Smaller low head weirs and dams kill humans.
Lots of time, money, and effort is going into removing smaller dams and low head weirs.
I feel like we still have some problems with dam building, because they keep failing. We struggle to get the building material (in particular, sand). Concrete is pretty awful in terms of CO2. Dams of all sizes cause problematic changes to the rivers they're on, and block flows of fish and other animals. Smaller low head weirs and dams kill humans.
Lots of time, money, and effort is going into removing smaller dams and low head weirs.