1. Water Conveyance and Control
M. U. Kale
Asstt. Prof.
CAET, Dr. PDKV, Akola

2. Water Conveyance and Control
Terminology
Open channels:
An open channel is defined as any conduit in which water flows with a free-water surface.
Pipe Flow :
It is a flow with no free water surface

3. Terminology Steady flow: It is the flow that does not change with time
Unsteady flow:
It is the flow that changes with time at a channel cross section

4. Terminology Uniform flow:
When a channel flow is steady and the mean velocity is the same at each succeeding cross-section, then flow is called as uniform flow.
Non Uniform flow:
When the mean velocity changes from cross section to cross section, the flow is called as non-uniform.

5. Types of channel Unlined Channel –
These are earthen channels without any coating on it’s bottom and sides.
Lined channel –
These are earthen channels with coating (of cement plaster, concrete, stones etc.) on it’s bottom and sides with the purpose of reducing water losses as seepage and percolation

6. Advantages of Unlined Field Channels
These are understood and accepted by farmers.
They can build and maintained by unskilled persons and require no special equipment or material.
Low initial cost
Build with stable slide slopes and with strong banks.
Permissible Slope of earth channels-
A channel slope about 0.1%, but silting may take place in the channel if slope is less than 0.05%
Assignment - Example 5.1

7. Lining of Channel
Water losses in water courses and field channel may occur
by seepage,
by breaches along the channel through rat holes,
by ponding of water in depression and irregularities in the channel sections and
by evaporation.
The loss by seepage depends on the length of the water course, its wetted perimeter and the intrinsic permeability of the strata through which the channel passes.
Earthen channels require continuous maintenance to control moss and weed growth and to repair damage by livestock, rodents and erosion.
Earthen channels are lined with impervious material to prevent excessive seepage and growth of weed in channels.
Materials commonly used for lining of water courses and field channels are
concrete and brick
stone masonry.

8. Channel Cross Section Channels are mainly of three cross sections
Trapezoidal
Rectangular
Semi-circular
The most efficient cross section for an open channel is one having
Minimum wetted perimeter and maximum hydraulic radius
Semi circle is most efficient cross section as the wetted perimeter would be minimum and its hydraulic radius maximum. It is given by
b = 2 d tan (ө /2)
In which
b = Bed width; d = Depth of flow
ө = The angle between the side and horizontal
Rectangular cross section having a depth of about half its width has been economical i.e. d = b/2
Most lined channels are trapezoidal in shape.

9. Water Conveyance through open channel

10. Design of open channel flow
Wetted perimeter: It is the sum of the length of that part of the channel sides and bottom which are in contact with water.
p = b + c + c
Area of cross section: It refers to the area of the wetted section of the channel.
a = (b+t) d / 2
Hydraulic radius: It is the ratio between the cross sectional area of the stream and its wetted perimeter.
R = a/p
V  (R)0.5
Hydraulic slope: It is the ratio of its vertical drop ‘h’ for a length ‘l’ of the channel.
S = h/l
Free-board: It is the vertical distance between the highest water level anticipated in the design and the top the retaining banks .

11. Estimation of velocity of flow in open channels
Discharge Capacity of Channel is given as
Q = a v
Where, Q = Discharge rate, m3/sec
a = Cross sectional area, m2
v = Mean velocity in the channel, m/sec
Mean velocity of flow is a function of
i) hydraulic roughness of the channel,
ii) hydraulic radius and
iii) hydraulic slope.
V = f (n, R, S)

12. Estimation of velocity of flow in open channels
Mean velocity of flow is determined by using following relationships.
Chezy’s formula -
Manning’s formula –
Darcy-Weisbach formula -

13. Estimation of velocity of flow in open channels
In which : v = Mean Velocity, m/sec. R = Hydraulic radius, m S = Hydraulic Slope, dimension less g = Acceleration due togravity,m/sec2 f = Darcy-Weisbach roughness coefficient or friction factor, dimensionless c = Chezy’s roughness coefficient n = Manning’s roughness coefficient

14. Structures to control erosion in irrigation channels
Drop Spillway
Pipe Spillway
Chute Spillway

15. Structures to control erosion in irrigation channels
Drop structure –
This structure is used to discharge water in a channel from a higher level to a lower level.
It is open drop type structure.
This structure is used when drop is less than 03 m.

16. Structures to control erosion in irrigation channels
Pipe Drop Structures
Water can be safely discharged from higher level to lower level by providing a pipe drop.
This type of structure allows discharge of water through pipeline, leaving the bund or dam undisturbed.
Vitrified sewer pipes or concrete pipes made with bell joints or corrugated metal pipes are used as through conduit.
This structure is used when drop is more than 04 m ().

17. The velocity of flow of water in pipe drop spillways may be calculated from the following relationship obtained by applying the Bernoullis theorem:
Where
H = Difference in elevation between the water level at the upstream and downstream ends of the structure, meters
v = Velocity of flow in the pipe, meter per second
f = Coefficient of friction for the pipe (usually to be about 0.01)
l = Length of pipe, meters
g = Acceleration due to gravity, meters per second (9.81m/sec2)
d = diameter of pipe, metres
K1 K2 = constants (for pipe drop K1 =0.5, K2 =0.25)
Assignment - Solve examples 5.3

18. Structures to control erosion in irrigation channels
Chute Spillway
The chute spillway consists of an inlet channel and outlet section.
The structure may be made of concrete or stone or bricks laid in cement mortar.
It is constructed on steep slope. It is used where head drop is fairly large (5 to 6 m).
To minimize the problem of settling and undermining, chute spillway is constructed on foundation on solid ground or on fill that has been carefully compacted.
Chute channel are usually rectangular in cross-section
The length of the stilling basin varies from 1.0 to 1.5 meter under the normal range
The depth of the stilling basin is about 10cm below the bed level of the down stream channel

19. Water Control and Diversion Structures
Check gates,
Portable check dam,
Diversion boxes,
Turnout boxes,
Siphons and
Pipe turnouts

20. Water Control Structures
a) Check gate
It is sluice gate.
It is operated with the help of handle.
It is used to control the flow of water (depth of water) in the channel downstream
Check gates placed at intervals along the channel keep a satisfactory water level for applying water to field.

21. Water Control Structure
a) Portable Check Dam
They are placed in an irrigation channel to form an adjustable dam to control the elevation of the water surface upstream.
A check structure consists of a masonry or metal wall built across the channel provided with a suitable check gate.
Precast reinforced concrete check gates can be made in a form made of steel metal and provided with a slot farmers.
Plate steel gates or wooden boards may be used as stops for check gates.
To obtain a watertight seal, specially designed rubber strips are used.

22. Diversion Structures Diversion-
In carrying water to different farms or to different parts of the same farm it is necessary for the water course or the main channel to divert the stream in the proper channel.
Turnouts-
When water is to take from a lateral channel into a field distribution channel or form a channel into a field it is used. They may be portable or built-in. The most common turnouts are box, spiles and siphon tubes.
Box Turnouts

23. Diversion Structures Spiles- Siphon tubes-
The are made up of bamboo, concrete, baked clay pipes.
The size varies from 2.5cm to 10cm or more depending upon flow.
Siphon tubes-
They convey water over the channel bank into a field or furrow.
They are made of plastic, rubber or steel metal (aluminium or mild steel) and are commercially available in different sizes like from 2.5cm to 7.5cm.
Spile
Siphon Tubes

24. Structures at channel crossing
It is often necessary to carry irrigation channels across roads, hillsides and natural depression or drainage ways.
The following structures are used for above purpose
Flumes
Culverts
Inverted siphons

25. Structures at channel crossing
Flumes -
Flumes may be made of open channels or pipes which are often supported by pillars or may be affixed to bridges.
Steel, concrete or vitrified clay pipes are used.
The open channels, when used , are semi-circular metal pipes or rectangular or trapezoidal wooden channels.
If timber is used, it should be treated with a preservative like creosote oil to extend its life.

26. Structures at channel crossing
Culverts
The structure consists of masonry headwalls at the inlet and outlet ends connected together by a buried pipeline.
The earth covering over the pipe should not be less than 30cm, but preferably about 45cm.
At the outlet of the culvert a stilling basin of the type described under erosion control structures is usually required to prevent erosion downstream.
Low cost culverts made of concrete pipes of adequate capacity may be constructed for ditch crossing.

27. Structures at channel crossing
Inverted Siphons
It is more economical when a channel has to cross a wide depression or where the road surface lies close to the field surface.