Test: Irrigation Engineering- 1 - SSC JE MCQ

Wetted perimeter is given by 

Where Q = discharge in cumec

Wetted perimeter 

Electrical Conductivity (EC):

It is the reciprocal of the Electrical Resistivity. Quantitively the electrical resistivity is the resistance, in ohms, of a conductor, metallic or electrolytes, which is 1 cm long and has a cross-sectional area of 1 cm² at 25^oC.

Units:

EC = Reciprocal ohms/cm or mhos/cm.

Watershed canal: The canal which is aligned along any natural watershed is called a watershed canal.

Contour canal: A contour canal is an artificially-dug navigable canal which closely follows the contour line of the land it traverses in order to avoid costly engineering works such as boring a tunnel through higher ground, building an embankment over lower ground, or constructing a canal lock (or series of locks) to change the level of the canal. Because of this, these canals are characterized by their meandering course.

Side slope canal: A side slope canal is that which is aligned at right angles to the contours i.e along the side slopes.

Branch canal: An offtakes from the main canal is known as branch canal.

Dischage over an Ogee spillway is given by:

H_e = Total head upstream of the crest.

L = crest width

C_d = coefficient of discharge

C = constant, which is equal to

Sodium carbonate lining consists of 10% clay and 6% sodium carbonate. This lining is not durable. Asphalt lining is prepared by spraying asphalt (i.e. bitumen) at a very high temperature (about 150⁰C) on a subgrade to a thickness varying from 3 mm to 6 mm.

Berm: The narrow strip of land at the ground level between the inner toe of the bank and the top edge of the cutting is known as berm. The berms provide additional strength to banks and thus make it safe against breaches. The berms when fully formed performed the following functions:

i) Provide a bigger water way

ii) Protect the bank from erosion because of wave action

iii) Reduce the absorption losses and prevent leaks

iv) Provide a scope for future widening of the canal

v) Bring the saturation line within the embankment

Critical velocity of flow (V_o) given by Kennedy is 

Where, m = critical velocity ratio

D = Depth of water over the bed portion of a channel in meters

A land is said to be waterlogged when the air circulation is stopped in the root zone of the plant due to the rise in water table.

The main causes of waterlogging are as follows:

i) Inadequate drainage facilities

ii) Over and Intensive irrigation

iii) Presence of impermeable strata

iv) Nature of soil

v) Seepage from canals

vi) The topography of the land

Using the relation 

Δ → depth of water required (cm)

D → Duty (hectares per cumec)

B → Base period (days)

Δ = 100 cm,   B = 100 days

D = 864 hectares per cumec

For a smooth entry into the water, the regulators should be positioned at an angle that allows for a gradual and streamlined descent. This angle is typically less than 90 degrees, as an angle greater than 90 degrees would cause a more abrupt and potentially disruptive entry.

Discharge over a rectangular crest of a sarda fall is given by:

Where, L = Length of the crest in meters

B = top width of the crest in meters

H = depth of water in meters

Lysimeter is used to measure evapotranspiration. By recording the amount of precipitation that an area receives and the amount lost through the soil, the amount of water lost to evapotranspiration can be calculated.

The duty is defined as area irrigated in hectare when unit discharge flows for a base period B. It is measured in hectare per cumec.

If a channel is excavated with smaller width and flatter bed slope, then flow takes place and bed slope increases due to deposition of silt. With increase in bed slope, the depth of channel may also vary but width of channel remains same because channel is usually cohesive and resists erosion.

Final Regime: This is the ultimate state of regime attained by channel when the slope, width and depth are also adjusted as per requirement. Resistance of sides are overcome due to continuous action of water.

True Regime:  Practically, true regime is never attained.

Lacey’s theory is not applicable to initial regime. True regime is not attained, hence this theory is applicable to final regime channels.

The success of any irrigation enterprise depends on the efficiency of distributing sufficient supply of water to the irrigator. Each irrigator has to receive certain quantity of water proportionate to his extent in a canal system at the proper time to ensure him a good crop. This distribution of water is carried out by means of outlets otherwise called modules. Hence, proper design of an outlet, is of most importance not only to the canal engineer but to the irrigator also.

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 rabi crops are sown around mid-November, after the monsoon rains are over, and harvesting begins in April/May. The crops are grown either with rainwater that has percolated into the ground, or with irrigation.

The major rabi crop in India is wheat, followed by barley, mustard, sesame and peas.

Water that percolates through earth dams and their foundations can carry soil particles that are free to migrate. The seepage forces tend to cause the erodible soil to move towards the downstream face of the dam and can cause failure of the dam which is known as piping failure. Downstream sheet pile is used to control failure due to piping.