This set of Irrigation Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Navigable Waterways Requirements”.
1. What is the minimum depth of water required for safe and economical navigation?
a) 1 m
b) 2 m
c) 2.7 m
d) 4.2 m
Explanation: The availability of sufficient water depth in the waterway is the chief requirement for navigations and for safe and economical navigation, a minimum depth of 2.7 m is generally required. Lesser depth in the rivers completely eliminates the possibility of towing the ships and causes an increase in the unit cost of transport and a depth of 3.7 m is generally desired in the final development.
2. The transit time required by a barge tow moving upstream in a navigable river increases if the flow velocity is more.
Explanation: The flow velocities should be low as high velocity causes a substantial reduction in the true speed for tows moving upstream. This increases the time of transit and cost of transport per kilometer. The speed of the barge tows in still water is almost 2.8 m/sec.
3. The belt conveyor forming an essential part of a ladder dredger used for excavating river sand deposits is used for _______________________
a) excavation of sand
b) transporting excavated sand to the surface over small distances
c) transporting excavated sand to the surface over large distances
d) transporting excavated sand to the surface over all distances
Explanation: Ladder dredger has an endless chain of buckets for bringing the excavated material up to the surface and the cuttings carried by buckets are discharged on a belt conveyor. The material is then disposed of through a stacker conveyor at the rear of the dredger which is limited in length to about 100 m or so.
4. The dredger which excavates sand deposits of a river and discharges the excavated material with water over long distances is called a _________________
a) ladder dredger
b) suction dredger
c) dipper dredger
d) upper dredger
Explanation: Dipper dredgers are used on small projects and are merely floating power shovels. Ladder dredger is used when the excavated materials are to be discharged at a considerable distance from the dredge. The disadvantage of the suction dredge is that it cannot operate in rocky or Shoulder River reaches.
5. Lock and dams constructions for creation of a series of slack-water pools along a river for promoting its navigability is adopted only when ________________________
a) the river is perennial
b) the river carries heavy sediment load
c) the available water in the river is quite less
d) the available water in the river is quite large
Explanation: This arrangement is generally adopted where existing site conditions are not favorable for adopting open channel methods. The water is required for lockage, sanitary releases, evaporation, percolation, etc and the requirement is much less than that of open channel procedures. Hence, it is adopted when the water available is less.
6. Timber is generally transported in our country through ________________
a) rail routes
b) road routes
c) air routes
d) water routes
Explanation: Very heavy items like cargo are also packed on wagon trains or trucks is lifted and transported through water transport. Besides the fact that it is the cheaper mode of transport, it is also used for recreational boating. The imports and exports are done by means of water routes.
7. What is the oldest and cheapest mode of transporting cargo?
a) Rail routes
b) Road routes
c) Air routes
d) Water routes
Explanation: Water transport is cheaper because the coefficient of friction on the water is small. On the water, one horsepower can pull 4 tonnes while on road and rail, it can move approximately 0.15 tonne and 0.5 tonnes respectively.
9. Ships or steamers can pay to carry cargo in Indian waterways extending to about ____________________
a) 500 km
b) 2500 km
c) 10,000 km
d) 40,000 km
Explanation: There is about 15,000 km length of navigable waterways in India and most of them are in bad conditions due to poor silting and maintenance. Most of it is fit only for boating and the streamers can ply only for about 2500 km length. For the total navigable length of about 15,000 km, about 8000 km is on rivers and 7000 km is on canals and backwaters.
10. The alignment of the waterway should be________________
d) irregular alignment
Explanation: A highly irregular alignment increases the circuitry or length in excess pf airline distance which the barge tow must travel. The existing channels generally have a length of about 50% greater than the air-line distances. Hence, the alignment should be as straight as possible.
10. The rivers carrying huge sediment load can be corrected with the help of sal-balli spurs.
Explanation: The rivers carrying little sediment load can be corrected by properly placed impermeable spears or jetties. When the rivers carry heavy sediment load, it can be corrected by permeable spurs called sal-Balli spurs driven at some suitable distance center to center in rows across the river currents. This slows down the current and promotes silting in the dyked area.
11. Which of the following dredger is not suitable for rocky or boulder river reaches?
a) Suction dredger
b) Ladder dredger
c) Dipper dredger
d) Both ladder and dipper dredger
Explanation: In suction dredgers, the suction head is provided with jets or rotating blades so as to cut or loosen the bed material and the suction openings through which the soil and the water mixture enters into the suction pipe. It cannot operate on rocky or Boulder River reaches. These dredgers can make cuts of about 10 m width through sand bars in order to achieve wider cuts.
12. The fuel consumption in water transport decreases as the depth of water between the bottom of the ship and the bottom of the river increases.
Explanation: The fuel consumption in water transport also depends on the available draft. When the clear depth between the barge and the river reduces, an increased drag force is developed which increases the consumption of fuel. If the clear space is increased from 0.6 to 1.5 m or so the fuel consumption can be reduced by about 25%.
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