Test: Design of Canals - Civil Engineering (CE) MCQ

An inundation canal is a canal which gets its supplies only when the water level in the river from which it takes off rises during floods.
Inundation canal

• An inundation canal is the one which gets its supplies only when the water level in the river, from which it takes off rise during floods.
• These canals are not provided with any headworks for diversion of river water to the canal but obtain their supplies through open cuts in the bank of the river, which are called "heads."
• The inundation canal are therefore non-perennial canals and the flow in these canal depend on the periodical rise of water level in the river.

Feeder canal

• A feeder canal is the one which is constructed only to feed another canal.
• No. direct irrigation is carried out from a feeder canal.
• It is also known as feeder.
• One of the important examples of feeder canal is Indira Gandhi feeder canal.

Ridge canal or watershed canal

• A ridge or watershed canal is the one which is aligned along the ridge or the natural watershed line.
• When the canal runs on a watershed it can irrigate areas on both sides and hence a large area can be brought under construction i.e. the canal has a higher command area.
• Further no drainage can intersect a ridge line or watershed, as all the drainage flow away from the ridge line, a ridge canal does not cross drainage line and hence for this canal cross drainage works are not required to be provided.

Contour canal

• A contour canal is the one which is aligned nearly parallel to the contours of the country.
• It can irrigate area only on one side. As the ground level on the other side is higher it is not necessary to construct a bank on the side. Such a canal with only one bank is know as single bank canal.
• When both the banks are provided it is know as double bank canal.

Design a regime channel for a discharge of 90 cumecs and silt factor of 1.3 using lacey theory

• Velocity as per the lacey theory
  
• Hydraulic mean depth
  
• wetted perimeter
  P = 4.75 √ Q = 4.75 √90 = 45.062 m
• Area of rea=ctangular channel = B × 

Now, Hydraulic mean radius = 
Area = 1.97 × 45.062 = 88.77 m²
1.5 BD = 88.77 
D = 88.77/1.5B = 59.18/B
The area of the rectangular channel, A = B × D and the perimeter for the same is given by P = 2D + B
From the equation of perimeter, we can write
45.062 = 2 × D + B
45.062 = 2 × D + 88.77/D
2 × D² - 45.062 × D - 88.77 = 0
Solving the above quadric equation we get
D = 2.181 and 20.34 m
20.34 m is not possible, so the design depth of the section will be 2.181 m
And we know, A = B × D
88.77 = B × 2.181
B = 40.701 m is the width of the section
Slope as per lacey is given by

S = 2.19 × 10^-4 = 1/4566 ≈ 1 in 4566
NOTE: None of the given options exactly match the correct answer, so we have to go for the most appropriate answer in this case, which is option A

As per IS 10430 : 2000, the maximum permissible velocity in different types of canals is given below in tabulated form: 

The velocity is limited to avoid scouring in canals.

Alignment of the canal

• Irrigation Canals are generally aligned along the ridge line. The main purpose of aligning a canal is to make sure that the water reaches the field by gravity.
• Irrigation Canals are generally aligned along the ridge line as it ensures gravity irrigation on both sides of the ridge.

Navigation Canal

• A navigation canal is constructed to provide various navigation facilities.
• The velocity of flowing water should be small for easy movement of small ships and barges in the direction of the flow of water as well as in the opposite direction.

Additional Information
Ridge Canal

• It is also called a watershed canal.
• Aligned along the ridge or natural watershed line.
• Can irrigate areas on both sides of the ridge.
• Cross-drainage work not requires.
• They are economical.

Contour Canal

• Aligned nearly parallel to the contours of the country.
• Can irrigate areas only on one side.
• Cross-drainage works are required.

Side Slope Canal

• Aligned roughly at right angles to the contour of the country.
• It is neither on the watershed nor in the valley.
• In can irrigate areas only on one side.
• It is roughly parallel to the drainage of the country, so cross-drainage works are not required.
• It has a very steep bed slope.

Lacey's scour depth is given by:

Where, q = Discharge per meter width, f = silt factor

Calculations:
Given, q = 3 cumec, f = 1.2

Important Points
Various formulas deduced by lacey is given below:

Based on Alignment Canals are classified into 3 categories. These are:
1. Ridge Canal, 2. Contour Canal and 3.  Side Slope Canal
Their characteristics are given below:

Lacey's scour depth is given by:

Where, q = Discharge per meter width, f = silt factor
Calculations:
Given, q = 3 cumec, f = 1.2

Important Points
Various formulas deduced by lacey is given below:

Whenever the available natural ground slope is steeper than the designed bed slope of the channel, the difference is adjusted by constructing vertical drops or falls in the canal beds at suitable intervals.
The main aim of constructing fall is to destroy the surplus energy build-up due to the difference in Energy head at the drop location.
Various types of famous falls are: Ogee falls, Trapezoidal notch falls, Well type falls, Sarda Type falls, etc.

Inundation or Diversion irrigation:
It is a type of irrigation system in which a large quantity of water flowing in a river during the flood is allowed to flood or inundate the land to be cultivated.
Inundation canals usually flow only during the summer months and bring in a large quantity of silt beneficial to crops.
Inundation irrigation is done by a canal taking off from a river in flood without any diversion work.
When the water available at higher level is supplied to lower level by the action of gravity only, then the type of irrigation is called flow irrigation.
When the dam is constructed across a river to store water during monsoons, so as to supply water in the off-taking channels during period of low flow, then it is termed as storage irrigation.
In Combined scheme, Dam is constructed across a river to form a reservoir, the stored water is used to produce electricity apart from irrigation purpose.

As per Lacey’s theory-
Hydraulic radius (R) is given by,

Where,
V is the flow velocity
f is silt factor
Calculation:
Given,
v = 1.5 m/s, f = 1
Hydraulic mean radius,

= 5.625 m
Important Points
Following relations are used in Lacey's Theory
The velocity of flow is given by V = 
Where,
f = silt factor = 1.76√d and d = average size of soil particles in mm.
Q is discharge , Area of the section is given by A = Q/V
Perimeter is given by, P = 4.75√Q
Bed slope(S), is given by S =