The stretch of river above or below a hydraulic structure (dam). The section below the dam is called the downstream section and the section above the dam is called the upstream section.

Bjef (fr. bief) - Part of a river, canal, reservoir or other body of water adjacent to a hydraulic structure. The principle of a spillway. Structures that may have an overflow are dams, sluices, hydroelectric power stations and others. There is an upstream headwater and a downstream tailwater on the other side of the structure. The upstream side is often a reservoir. A backwater formed by two or more water-retaining structures and located in a watershed section of a water system or watercourse is called a separate backwater.