Which of the following statement is correct for sprinkler irrigation method?
In this method Irrigation water is applied to the land in the form of spray. The sprinkler irrigation is used for all the crops except rice and jute and for almost all the soils except very heavy soils with very low infiltration rates.
In this method, borders and field channels are not required and hence more land is available for cropping.
Capacity of an irrigation tank depends on:
The rate at which water can be extracted from the tank is known as capacity of the tank. Capacity of irrigation tank depends on the type of crop and its duty.
Acidic soils are reclaimed by:
Due to the presence of injurious salts like Na2CO3, Na2SO4 and NaCl, Soil will become saline which lead to efflorescence and if it continuous for a longer time then the soil will become alkaline. These soils are reclaimed by leaching, crop rotation, providing sub surface drainage area, addition of gypsum etc.
On the other hand, acidic soils can be reclaimed by basic salts such as limestone.
The Lacey’s silt factor for a particular alluvium is 2.0. This alluvium would comprise:
Lacey’s silt factor is given by:
A check dam is a:
Check dams are small barriers built across the direction of water flow on shallow rivers and streams for the purpose of water harvesting. The small dams retain excess water flow during monsoon rains in a small catchment area behind the structure.
The check dam
- could be designed to create small reservoirs
- reducing the velocity of flow in the channel
- can counteract erosion
- avoid silting
- increases groundwater recharge
The base width of a solid gravity dam is 25 m. The material of the dam has a specific gravity of 2.56 and the dam is designed as an elementary profile ignoring uplift. What is the approximately allowable height of the dam?
For elementary profile of the dam,
Base width of the dam is given by:
When uplift is ignored, C =0
At a certain point in the floor of weir, the uplift pressure head due to seepage is 4.5 m. If the relative density of concrete is 2.5, the minimum thickness of floor required at this point to counteract the uplift pressure is:
Minimum thickness of floor required is,
In a river, silt excluder and silt ejector are constructed:
Silt excluders are constructed on the bed of the river, upstream of the head regulator. While silt ejectors are constructed on the bed of the canal and a little distance downstream from the head regulator.
As, Silt excluders remove silt from the water before it enters the canal and silt ejectors extract the silt from the canal water after the silted water has travelled a certain distance in the off-take canal.
The most economical method of soil conservation is to:
Afforestation means planting trees. As we know, the roots of the trees help to hold the soil layer firmly, it is evident that it helps not to make the soil loose and prevents erosion.
Thus by planting more and more trees, the top layer of the soil becomes less prone to erosion by wind, water etc. Hence it prevents erosion and helps in soil conservation.
Note: Contour bunds and check bunds are basically water harvesting techniques.
Outlet discharge for a particular crop is given by:
The duty at the head water course is called as “outlet Discharge factor”.
The ratio between the area of the crop irrigated and the quantity of water required during its entire period of growth is known as duty. Duty is measured in hectares per cumec.
Outlet factor =
The alignment of a canal:
i) The canal which is aligned along the *water-shed line* is known as ridge canal. Canal can also be aligned along contours of the country, right angle to contours of the country but the most economical is ridge canal. The advantage of this type of canal is that it can irrigate the areas on both the sides.
ii) As per financial perspective of the country, canal should not be located near-by our valuable properties because of problems in flood like situations.
iii) It should be so aligned such that minimum number of cross drainage work is required.
The loss of head per unit length of the creep is called:
According to Bligh’s creep theory, the percolation water creeps along the base profile of the apron with the sub-soil. The path traced by the percolating water is known as creep length and the head loss per unit creep length is known as hydraulic gradient or percolating coefficient.
In a river, spurs are provided:-
Groynes or spurs are constructed transverse to the river flow extending from the bank into the river. This form of river training works performs one or more functions such as:
i) Training the river along the desired course to reduce the concentration of flow at the point of attack,
ii) Creating a slack flow for silting up the area in the vicinity and protecting the bank by keeping the flow away from it.
Groynes are adopted for river bank protection works. When it is placed inclined downstream in the direction of flow in the river, it is designated as which one of the following?
A drop in canal bed is generally provided if:
Canal fall is solid masonry structure which is constructed on the canal if the natural ground slope is steeper than the designed channel bed slope.
If the difference in slope is smaller, single fall can be constructed. If it is of higher then falls are constructed at regular intervals.
If the discharge required for different crops is 0.6 cumecs in the field and the capacity factor and time factors are 0.8 and 0.5 respectively, then what is the design discharge of the distributary at its head?
If D is the depth of scour below original bed, then the width of launching apron is generally taken as:
Heavy scour of the river bed at curved heads and shanks of guide banks can cause undermining of stone pitching thereby resulting in failure of guide banks. Such a failure can be prevented by providing launching apron beyond the toe of guide banks. The width of launching apron is generally taken as 1.5D.
The ratio of the water stored in the root zone during irrigation, to the water needed in the root zone prior to irrigation is called:
i) Water Conveyance Efficiency, (ηc)
where, Wf = Water delivered to the field
Wr = Water delivered from the reservoir
ii) Water Application Efficiency (ηa)
where, Ws = Water stored in the root zone
Wf = Water delivered to the field
iii) Water use Efficiency (ηu)
where, Wu = Water use consumptively.
Wf = Water delivered to the filed
iv) Water storage Efficiency (ηu)
where, Ws’ = Actual water stored in the root zone
Wf = Water needed to store to bring the water content up to field capacity.
v) Water distribution Efficiency, (ηd)
where, y = Average numerical deviation in the depth of water stored from the average depth of irrigation stored
d = Average depth during irrigation
vi) Consumptive use Efficiency (ηcu)
where, Wcu or Cu = Water used by plant consumptively.
Wd = Net amount of water depleted from root zone.
A constant centre (in plan – view) arch dam is best suited for:
Thession’s polygon is used for determination of: