Raising the water level in a river can also allow boats and ships to navigate areas that would otherwise be inaccessible. ... A weir is a small dam built across a river to control the upstream water level. Weirs have been used for ages to control the flow of water in streams, rivers, and other water bodies.

How do weirs control flow?

A weir /wɪər/ or low head dam is a barrier across the width of a river that alters the flow characteristics of water and usually results in a change in the height of the river level. ... There are many weir designs, but commonly water flows freely over the top of the weir crest before cascading down to a lower level.

How do weirs stop flooding?

Weirs stop natural processes and impact river channels in two main ways; Upstream – Sediment transport is interrupted by the weir, sediment (e.g. gravel) accumulates upstream. ... The river begins at one elevation and incises downward through its bed while leaving its floodplain behind [higher]) throughout its course).