Area upstream of a dam where water is or can be stored for a long period of time (several weeks and sometimes months). A large reservoir can regulate (or alter) the flows in the downstream river section.
Type of hydroelectric facility where no or little water is stored. A dam is built to cause water to pond upstream, ensuring the river water is high enough to enter the pipes leading to turbines. A run-of-river facility has little ability to regulate (or alter) the flows in the downstream river section.
The excess water, from precipitation or spring melt, which isn’t retained in the ground and flows into the surrounding streams.