This set of Irrigation Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Design of Modern Weirs and Barrages”.
1. Into how groups the design of a barrage is divided?
Explanation: The complete design of a barrage or a modern glacis weir is divided into two groups, namely hydraulic design and structural design.
2. Hydraulic design when used on the permeable foundations, the design is classified into two groups.
Explanation: When a hydraulic design is used for a weir on the permeable foundations, then the design is classified into two aspects, namely design for subsurface flow and design for surface flow.
3. How many types of aspects are determined by using the hydraulic design in design for a weir?
Explanation: The hydraulic design of a weir involves determining the section of the weir, details of upstream cutoff, crest, glacis, floor, downstream cutoff, and protection works of upstream and downstream.
4. Khosla’s method of independent variables is useful in hydraulic design.
Explanation: The method of independent variables given by Khosla can be used to determine the uplift pressures exerted by the seeping water on the floor of the weir.
5. Which factor should be kept in safe limits to avoid failure of structure?
a) Seeping Pressure
b) Exit Gradient
c) Side Slopes
d) Velocity of Flow
Explanation: To ensure the safety of the structure or to say to protect the structure from failure due to piping, the exit gradient should be kept within the safe limits.
6. By how many factors the design of protection works is based?
Explanation: The protection works are needed both on the upstream and downstream side to prevent the scour hole which is travelling close to the pucca floor of the weir and to relieve the uplift pressure. So, in order to achieve this, the protection arrangement consists of an inverted filter and launching apron.
7. The inverted filter used in protection arrangement, protects the weir from what?
a) Silting Action
d) Leakage Problems
Explanation: It helps in reducing the possibility of piping by allowing the flow of seepage water through it, without allowing the foundation soils to be lifted up. Therefore the filter consists of layers of materials of increasing permeability from bottom to top.
8. How many factors govern the design a weir or a barrage?
Explanation: The information or rather say the data pertaining to these factors, namely high flood levels for the river at the weir site, river cross section at the weir site, stage discharge curve at the weir site, and maximum flood discharge for the river at the weir site are to be collected before designing a weir or barrage.
9. On par with retrogression factor, how many other certain factors are to be considered?
Explanation: Apart from retrogression, other factors like crest levels, afflux, waterway and discharge per meter, and pond level are to be decided while designing a weir or a barrage.
10. What is the name given to the first effect created by the construction of a weir?
a) Crest Damage
Explanation: Whenever a weir is constructed the first effect will be that the downstream bed of the river goes on eroding, continuously causing a progressive lowering of downstream levels. So, therefore this progressive lowering of downstream levels is known as retrogression of downstream levels or retrogression.
11. What is the basic cause of retrogression?
a) Flood Levels
b) Seepage Pressure
c) Silt Carrying Capacity
d) Fault in the Design of Protection Works
Explanation: The main cause of retrogression is the silt carrying capacity of the channel. This is explained as when a weir is constructed the upstream side losses it silt carrying capacity due to the formation of shoals and islands. So, therefore in order to fulfil the increased demand of the silt carrying capacity of the channel in downstream side progressive erosion takes place on downstream side leading to retrogression.
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