This set of Irrigation Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Location of Spillway”.
1. The safety valve of a dam is its __________________
a) drainage gallery
b) inspection gallery
d) outlet sluices
Explanation: A spillway is essentially a safety valve for the dam and must be properly designed. It should have adequate capacity to dispose off the entire surplus water from upstream to downstream at the time of the arrival of the worst design flood.
2. An ungated spillway starts functioning as soon as the water level in the reservoir crosses the __________________
a) maximum reservoir level
b) minimum reservoir level
c) maximum conservation level
d) full Supply level
Explanation: Maximum conservation level is nothing but normal pool level which is the maximum elevation to which the reservoir water surface will rise during normal operating conditions. This is equivalent to the elevation of the spillway crest or the top of the spillway gates, such uncontrolled spillways are only guided by the available water head.
3. Which of the following is the simplest type of spillway and may be constructed on small bunds or thin arch dams?
a) Straight drop spillway
b) Ogee spillway
c) Shaft spillway
d) Siphon spillway
Explanation: Straight drop weir or Overfall spillway is a low weir and simple vertical fall type structure. It is the simplest type of spillway and can be constructed on small bunds, thin arches, etc. The downstream face of the spillway may be kept vertical or slightly inclined.
4. The spillway can be best built independently of the dam when there is _________________________
a) deep narrow gorge with steep slopes
b) deep narrow gorge with gradual slopes
c) wide gorge with a gradual slope
d) wide valley with moderate slopes
Explanation: The spillway can be best built independently of the dam where there is a deep narrow gorge with steep banks separated from a flank by a hillock with its level above the top of the dam. A concrete or an earthen dam can be constructed across the main valley and a spillway can be constructed independently into the saddle under such circumstances.
5. Which of the following is a secondary safety arrangement?
a) Safety valves
b) Spillway gates
c) Subsidiary spillway
d) Energy dissipaters
Explanation: If at the worst condition the water rises above the maximum reservoir level it will overtop such an embankment. A secondary safety arrangement known as subsidiary dam or emergency spillway or breaching section is generally provided on large dams for the disposal of excess water, especially on earthen and rock-fill dams.
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