According to material used and certain design features, gravity weir is sub-divided into three groups. They are vertical drop weir, sloping weir, and parabolic weir. Sloping weir is again classified into two groups, namely masonry slop weir and dry stone slope weir.

In gravity weir, uplift pressure is due to seepage of water below floor and is resisted entirely by weight of floor.

In non-gravity type weir thickness of floor is relatively kept less, and uplift pressure is largely resisted by bending action of reinforced concrete floor.

This type of weir is suitable for kind of foundation because it is provided with or without crest gates, cutoff piles are provided at both upstream and downstream, to protect against scouring aprons are provided at both up and down streams, and at downstream to relieve uplift pressure graded inverted filter is provided.

The figure represents a sloping weir made up of dry stone or rock fill. It also represents body walls at both upstream and downstream sides and rock falls laid in form of glacis with few intervening core walls.

Weir is an obstruction across river to raise its water level and divert into new channel. It can also store water for short duration of time of short supplies, known as storage weir. The only main difference between dam and weir is that dam can store water comparatively for longer duration than weir and dam is at more height than weir.

Barrage is almost a similar structure like a weir, but difference is that barrage is not a solid obstruction across a river and moreover heading of river is controlled by gates alone. The crest level in barrage is kept at low level. During floods gates are kept for discharge of excess waters and when flood recedes gates are lowered, thus solving silting problem.

This weir is similar to spillway section of a dam. The body of this weir is kept as a low dam. A cistern is provided at downstream side for energy dissipation of falling waters from upstream to downstream side.

This type weir is of recent origin. They are much suitable for soft and sandy foundations and are generally used when difference between weir crest and downstream river bed is limited to 3 metres.

Mainly four causes are responsible for failure of weirs. They are piping, rupture of floor due to uplift, rupture of floor due to suction caused by standing wave, and scouring at upstream and downstream side of weir floor.