Difference Between Weir and Dam

Man has always been in a constant struggle to make optimum use of the flowing waters of rivers. He has tried to build high brick and mortar structures across the river to control the flow of water so as to use the water for agriculture, drinking, and also for electricity generation. Weirs and dams are two structures that are commonly created across a river for these purposes. Thou most of us are aware of the concept of dams and many of us have actually seen dams, no many know what a weir is. This article will clearly explain the differences between a weir and a dam along with their function and features.

Dam

Dam is a high wall of concrete that is erected across a river to impound water behind the wall and also to increase the flow of water to be used for power generation. The water collected in the reservoir behind the dam is used for distributing to areas that are deficient in water and also for supply of drinking water to the populace in the cities around the dam. The very fact that man has been using such high walls for thousands of years to make use of the uncontrolled water of meandering rivers speaks volumes of the ability and intelligence of mankind to provide water to areas with less water and for drainage in agriculture. One has to see the ingenuous designs of dams in different parts of the world across rivers to really complement the clever use of walls to maximize the potential of flowing rivers. Hoover Dam across Colorado River is one such example.

Weir

Weir is a type of dam that is constructed across a river mainly to control the flow of water. Unlike dams, they are smaller in size and the obstruction they create with the wall across the river has a specially designed opening such as a rectangle or a triangle or V shaped opening that gives more thrust to the flowing water. The structure called weir results in an increase in the water level or head which can be measured upstream, of the structure. Rectangular, triangular and broad crested weirs are more common. Weirs are broad crested if made of timber and concrete and thin crested if the crests are made of thin metal plates.

A weir is also referred to as a low head dam as it is a structure across the stream that causes a build up of water behind this structure. The water collected behind the structure is used for power generation or recreation, though it is also used for making canals to take water to areas that have less water, and for supplying drinking water in the nearby inhabited areas.

Weirs are useful and serve many purposes but they create very forceful hydraulic wave that has been known to kill people through drowning.