Engineering Geology Multiple Choice Questions on “Geological Investigations and Silting”.
1. What is the shape of valley usually preferred for a reservoir?
a) U-shaped
b) V-shaped
c) Flat lands or plains
d) U or V-shaped
Answer: d
Clarification: The valley could be a U-shaped glacial valley, or a V-shaped river valley or a broader synclinal valley. Flatlands and plains cannot make convenient places for reservoirs.
2. During which condition, permeability of rocks have to be given more importance?
a) When general water is much above the top reservoir level
b) When general water table is much below the minimum water level
c) When general water table and top water level of the proposed reservoir are almost same
d) When general water table is slightly above the top reservoir level
Answer: b
Clarification: When the general water table is much below the minimum water level in the reservoir, permeability of the rocks along the base and the flanks is taken into consideration.
3. Which is the ideal condition for a reservoir?
a) When general water is much above the top reservoir level
b) When general water table is much below the minimum water level
c) When general water table and top water level of the proposed reservoir are almost same
d) When general water table is slightly above the top reservoir level
Answer: c
Clarification: The general water table of the area and the top water level of the proposed reservoir are almost the same. This is an ideal situation ensuring a no loss no gain condition but generally not available on a large scale.
4. Heavy load of sediments to reservoirs would reduce __________
a) Flow of water in that area
b) Effective storage
c) Total life of reservoir
d) Total life and effective storage of reservoir
Answer: d
Clarification: The run off and slope wash would contribute heavy load of sediments to the reservoir after every rain. This would obviously decrease the effective storage capacity of the reservoir on one hand and its total life on the other hand.
5. Which among the following need not be given prime importance during geological investigation?
a) Groundwater conditions
b) Wind conditions
c) Structural constitution
d) Trend and rate of weathering
Answer: b
Clarification: Since reservoirs are essentially water storage basins, the area should possess such geological characteristics that favour holding of water in the basin so created. Such characters are: topographic suitability, ground water conditions, permeability and structural stability and also trend and rate of weathering.
6. Removal of silt is usually __________
a) Time consuming
b) Energy consuming
c) Money consuming
d) Time, energy and money consuming
Answer: d
Clarification: Removal of silt or methods of sedimentation control may be so much time and energy and money consuming that the economy of the project is sometimes threatened. These facts prove the complicated nature of the problem.
7. The major problem in a reservoir over time which may affect the storage capacity is __________
a) Leakage
b) Silting
c) Reduction in rainfall
d) Weathering of side slopes
Answer: b
Clarification: Sedimentation of reservoirs with the passage of time is the most important problem to solve in reservoir design. Uncontrolled sedimentation will lead to the indirect failure of the project by gradually reducing the storage capacity.
8. Pick a method to control silting.
a) By grouting
b) By reducing water level
c) Construction of check dams
d) By constructing lining on the rock foundation
Answer: c
Clarification: Important methods of treatment include better reservoir designs, installation of check dams at the inlet points and water-shed improvement by forestation on an extensive and intensive scale.
9. De-silting methods are very expensive.
a) True
b) False
Answer: a
Clarification: Removal of silt after fixed intervals by dredging and similar methods are also practised in many cases. All these are, however, very costly methods and any one or more of them are adopted in combination after careful analysis of cost benefit ratio.
10. Flatlands and planes can make convenient places for reservoirs.
a) True
b) False
Answer: b
Clarification: The valley could be a U-shaped glacial valley, or V-shaped river valley or a broad synclinal valley. Flatlands and plains cannot make convenient places for reservoirs.