Irrigation Engineering Multiple Choice Questions on “Diversion Head Works – Weir and Barrage”.
1. Into how many groups the gravity weir is sub-divided?
a) 5
b) 4
c) 3
d) 2
Answer: c
Clarification: According to the material used and certain design features, the 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.
2. In gravity weir, the uplift pressure is due to the seepage of water.
a) True
b) False
Answer: a
Clarification: In gravity weir, the uplift pressure is due to the seepage of water below the floor and is resisted entirely by the weight of the floor.
3. The uplift pressure in non-gravity weir is resisted by the bending action.
a) False
b) True
Answer: b
Clarification: In non-gravity type weir the thickness of the floor is relatively kept less, and the uplift pressure is largely resisted by the bending action of the reinforced concrete floor.
4. Which type of weir is suitable for any type of foundation?
a) Sloping Weir
b) Vertical Drop Weir
c) Parabolic Weir
d) Masonry Sloping Weir
Answer: b
Clarification: 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.
5. What type of weir does the diagram represent?
a) Parabolic Weir
b) Gravity Weir
c) Dry Stone Slope Weir
d) Vertical Drop Weir
Answer: c
Clarification: 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 the form of glacis with few intervening core walls.
6. What is the main difference between a dam and weir?
a) Height and Duration of Storage
b) Capacity of Water
c) Material used for Construction
d) Location of the Structure
Answer: a
Clarification: Weir is an obstruction across the 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 the dam is at more height than the weir.
7. What is the difference between a weir and a barrage?
a) Discharge Capacity
b) No Solid Obstruction
c) Storage Capacity
d) Velocity of Flow
Answer: b
Clarification: Barrage is almost a similar structure like a weir, but the difference is that barrage is not a solid obstruction across a river and moreover the heading of the river is controlled by gates alone. The crest level in barrage is kept at low level. During floods the gates are kept for discharge of excess waters and when the flood recedes the gates are lowered, thus solving the silting problem.
8. In which type of weir energy dissipation takes place?
a) Barrage
b) Vertical Drop Weir
c) Sloping Weir
d) Parabolic Weir
Answer: d
Clarification: This weir is similar to the spillway section of a dam. The body of this weir is kept as a low dam. A cistern is provided at the downstream side for energy dissipation of the falling waters from upstream to the downstream side.
9. Which type of weir is of recent origin?
a) Vertical Drop Weir
b) Masonry or Concrete Sloping Weir
c) Parabolic Weir
d) Barrage
Answer: b
Clarification: This type weir is of recent origin. They are much suitable for soft and sandy foundations and are generally used when the difference between the weir crest and downstream river bed is limited to 3 metres.
10. What number of causes is responsible for the failure of weirs?
a) 2
b) 4
c) 3
d) 1
Answer: b
Clarification: Mainly four causes are responsible for the 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 the upstream and downstream side of the weir floor.