Irrigation Engineering Questions and Answers – Chute Spillway

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This set of Irrigation Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Chute Spillway”.

1. Which of the following is the simplest type of spillway which can be provided independently and at low costs?
a) Ogee spillway
b) Trough spillway
c) Siphon spillway

Explanation: The trough or chute spillway is adaptable to any type of foundations and is the simplest type of spillway. It can be easily provided independently at low costs but it requires ample room adjacent to the dam.

2. If the spillway is constructed in continuation to the dam at one end, it may be called as ________
b) flank weir
c) waste weir
d) temporary weir

Explanation: Saddle weir is the one when the spillway is constructed in a natural saddle in a bank of the river separated from the main dam by a high ridge. Flank weir is the one when the spillway is constructed in continuation to the dam at one end.

3. The spillway which can be adopted with ease on gravity as well as earthen dams is _________________
a) ogee spillway
b) chute spillway
c) both ogee and chute spillway
d) straight drop spillway

Explanation: Straight drop spillway is a low weir and simple vertical fall type structure which may be constructed on thin arch dams or small bunds etc. An ogee spillway is most suitable for concrete gravity dams. Chute spillway can be provided easily on earth and rock-fill dams.

4. The famous Bhakra dam of India is provided with ________________
a) trough spillway
b) ogee spillway
c) shaft spillway
d) siphon spillway

Explanation: Bhakra Dam is a concrete gravity dam on the Sutlej River in Himachal Pradesh of the total height of 226 m approximately. It forms the Gobindsagar Reservoir with controlled overflow chute or trough spillway and four spillway gates for an emergency.

5. The surplus reservoir water after spilling over the crest of the spillway flows on the chute is __________________
a) parallel to the crest in a trough spillway
b) parallel to the crest in a side-channel spillway
c) perpendicular to the crest in a side-channel spillway
d) obliquely to the crest in a chute spillway

Explanation: In chute spillway, after crossing over the crest of the spillway water flows at right angle shoots down a channel or a trough to meet the river channel downstream of the dam. The water after spilling over the crest flows parallel to the crest in a side-channel spillway.

6. Whenever the slope of chute changes from steeper to milder ____________________ curve shall be provided.
a) a concave vertical curve
b) a convex vertical curve
c) a hyperbolic curve
d) a parabolic curve

Explanation: A concave vertical curve is provided whenever the slope changes from steeper to milder. The radius of this curve should be less than 10 times the depth of water (in meters).

7. The side slope of approach channel of chute spillway is ___________________
a) 1:1
b) 1:1 $$\frac{1}{2}$$
c) 1:3
d) 1:2.5

Explanation: An entrance channel also called as an approach channel is trapezoidal in shape with side slopes 1:1. It is constructed so as to lead the reservoir water up to the control structure or low ogee weir.

8. The spillway which may sometimes be called as a waste weir is ______________________
a) an ogee spillway
b) a trough spillway
c) a shaft spillway
d) a siphon spillway

Explanation: A chute or trough spillway is sometimes called as a waste weir. It is called as chute spillway because after crossing over the crest of the spillway water flow shoots down a channel or trough to meet the river channel downstream of the dam. The trough is taken straight from the crest to the river.

9. The portion of a chute spillway which is known as its control structure is ________________
a) low ogee weir
b) chute channel
c) approach channel leading the water from the reservoir to the ogee weir
d) silting basin at its bottom

Explanation: Low ogee weir is required as a control structure in the chute spillway. The entire chute spillway is divided into the entrance channel, control structure, Chute channel or discharge channel, and energy dissipation arrangements in the form of silting basin at the bottom.

10. The type of spillway which is provided on narrow valleys where no side flanks are available is ____________________
a) ogee spillway
b) chute spillway
c) side-channel spillway
d) straight drop spillway

Explanation: The side channel spillway is suitable when the valley is too narrow. When there is no room for provision of chute spillway (as side flanks of sufficient width are required), this type is adopted as it requires limited space. The situation required for the chute spillway and side-channel spillway is mostly the same.

11. Which of the following curve is provided when the slope of the chute changes from milder to steeper?
a) Concave vertical curve
b) Hyperbolic curve
c) Convex vertical curve
d) Straight plan

Explanation: A convex vertical curve shall have to be provided when the slope of the chute changes from milder to steeper. The curvature should approximate to a parabolic shape. A concave vertical curve is provided whenever the slope changes from steeper to milder.

12. Calculate the freeboard for the top levels of the side walls if the mean velocity of water in the chute reach is 3.5 m/s and the mean depth of water in the chute reach under consideration is 4.7 m.
a) 0.60 m
b) 1 m
c) 0.85 m
d) 0.55 m

Explanation: The freeboard to be provided above the top nappe of side walls is generally given by the equation:
F.B = 0.61 + 0.04 Vm. dm1/3 where ‘Vm‘ is the mean velocity of water in the chute reach and ‘dm’ is the mean depth of water in the chute reach under consideration.
F.B = 0.61 + 0.04 x 3.5 x 4.71/3 = 0.84 m.

13. The minimum slope of the chute is governed by the condition that _____________
a) the subcritical flow must be maintained
b) the supercritical flow must be maintained
c) a critical flow must be maintained
d) maybe supercritical or subcritical flow is possible

Explanation: The water flows through the chute channel after spilling over the control structure and the minimum slope is governed by the condition that the supercritical flow must be maintained. The slope should be sufficient to meet the flow requirement from the crest without endangering the stability or heavy excavations.

14. What is the approximate percentage of light reinforcement that is provided in the top of the reinforced concrete slabs at the base?
a) 0.50% of the concrete area
b) 0.45% of the concrete area
c) 0.30% of the concrete area
d) 0.25% of the concrete area