This set of Irrigation Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Canal Falls – Location”.
1. Canal drops are provided to _______________
a) dissipate the excess energy
b) increase the driving head of flow of water
c) dissipate excess land slope
d) dissipate inadequate land slope
Explanation: when a canal fall or drop is provided at a suitable section, it brings down the canal bed line. In this process, water comes down with a great force and all the potential energy is converted into kinetic energy. The excess energy of the flow is destroyed with some suitable energy dissipation method.
2. For a canal that irrigates the area directly the fall should be provided at a location FSL outstrips the G.L before the bed of the canal comes into the filling.
Explanation: This is done in case of branch canals and distributary channels which irrigate the area directly, the FSL is fixed and marked at the head of the off-taking channel and outlets. In the case of the main canal which does not irrigate the area directly, the site of the fall is determined by considerations of economy.
3. In case of branch canals and distributary channels, the falls are located with consideration to _________________
a) command area
c) cost economy
d) availability of earth material
Explanation: In the case of branch canals and distributary canals, the procedure is to mark the FSL required on the L-section of the canal. It is done so as to cover all the commanded points that decide the suitable locations for fall in canal FSL and in canal beds.
4. By providing a natural drop in one drop _______________________
a) the quantity of unbalanced earthwork decreases
b) the quantity of unbalanced earthwork increases
c) the quantity of balanced earthwork increases
d) number of fall increases
Explanation: The number of fall decreases and the quantity of unbalanced earthwork increases by providing a larger drop in one step. All these factors have to be worked out before deciding the locations and extent of falls.
5. A canal fall is provided when the available natural slope is flatter than the designed bed slope of the channel.
Explanation: When the ground has a steep slope heavy earth filling is required to construct the canal with a flatter bed slope. The difference between the natural slope and the designed bed slope is adjusted by constructing vertical falls or drops in the canal at a suitable interval.
6. Consider the following statements.
I. Possibility of combining some other structure with a fall eg. regulator, road bridge etc.
II. Cutting and filling are required below and above the fall should not be necessarily equal.
III. The command should not be reduced due to the lowering of F.S.L and the fall may be located below the outlets.
Which of the following statement is correct for site selection of a fall?
a) I only
b) III only
c) I and II
d) I and III
Explanation: The unbalanced earthwork is quite expensive so the excavation and filling on two sides of the fall should be balanced. The considerations of the economy in ‘cost of cutting and filling’ versus ‘cost of fall’ form a basis in deciding the site of a fall in case of the main canal.
Sanfoundry Global Education & Learning Series – Irrigation Engineering.
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