Hydraulic Parameters and Shear Stress And Stream Power

1. 19-07-2020 LMT 1

2. Open Channel flow is also called as – free Surface flow / gravity flow.
EXAMPLES : -
is a technology
and applied science using
engineering, chemistry, and
other sciences involving the
mechanical properties and
use of liquids
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3. Hydraulic Parameters
• Depth(d) of the channel, Width(w) of the banks and Velocity(v) of the water.
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4. • It can be measured by various
methods:
• Current meters
• Various Floats (light weight
wooden block or ball)
• By empirical formulae, etc.
• It is a ratio of width(w) and area
(A)of a cross section.
d = A/w
Hydraulic Parameters
• Depth(d) of the channel, Width(w) of the banks and Velocity(v) of the water.
• The width of the river is the
distance between the two points
on your side of the river times
the tangent of the angle. This can
also be solved by using any two
points on your bank of the river.
• Velocity(v) will change along the
course of any river, and is
determined by factors such as the
gradient the volume of water, the
shape of the river channel and
the amount of friction created by
the bed, rocks and plants.
• To measure the velocity :
Stream Discharge
The flow of water through
a stream channel is called stream
discharge. In most countries, it is
measured in cubic meters per
second. The following equation
defines stream discharge
mathematically:
Q = V x W x D
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5. Results according to Mannings equation obtain from each will be different
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6. Laminar/ uniform Turbulent non-uniformTo know whether flow is Laminar or
Turbulent:
REYNOLD’s NUMBER EQUATION
It is a ratio between the products of average velocity (v) and depth (d)
to the kinematic viscosity (द्रव्याचा चचकटपणा (विरघळेल पदार्थ जसे salt, minerals in river).
= rho – density of water
= mew – viscocity
Constants
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7. Types of flows in Fluvial -hydraulics
Types of flows
Laminar/ uniform
Turbulent non-
uniform
Streaming Flow/
Sub-critical flow/
Low flow regime
Shooting flow/
super-critical/
High Flow regime
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8. • Laminar flow - water flow in the stream is not altered in its
direction. Water flows as parallel molecular streams. (Such
type of flow is very rare in nature.)
• Turbulent flow - water flows as discrete eddies and whirls.
Caused by channel topography and friction with the river
bed
Other type of flow (given by engineers)
• Helical flow - spiral flow in a stream. Caused by channel
shape. Meandering channels cause this type of flow. Helical flow has an
important role in sediment transport and deposition, and in the creation
of point bars.19-07-2020 LMT 8

9. The open channel hydraulics is categorized as critical or sub-critical or super-
critical based on the Froude number Fe. Froude number is given by the
relation:
Froude’s number Fe or Fr.
Or Fr = v2 / g.D
Ratio between the square of mean velocity to the product of
acceleration due to gravity and depth of the water is called as
Froude number .
Fr < 1 = Streaming (stable flow) = Sub
–critical = Low flow regime
Fr > 1 = Shooting (turbulent flow) =
Super –critical = high flow regime
Fr = 1 = Critical flow (ideal condition)
= Critical flow
Shooting flow/
super-critical/
High Flow regime
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10. Shear Stress And Stream Power
• Shear Stress (t) is a measure of the force of friction from a
fluid acting on a river bed during the flow.
In the case of open channel flow, it is the force of moving
water against the bed of the channel.
• Stream Power is a combination of velocity and shear stress
• Hence the stream power is a basis of many sediment
transport formulae applied for modeling of sediment
deposition and erosion in rivers and reservoirs.
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11. Shear Stress
• Shear stress in fluids- Rivers
shear stress required to
mobilize sediments
delivered to the channel.
When the shear
stress equals the
critical shear stress, the
channel will likely be in
equilibrium.
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12. Stream power
Stream power is the rate of energy dissipation against the bed
and banks of a river or stream per unit downstream length. It is
given by the equation:
where Ω is the stream power, ρ is the density of water
(1000 kg/m3), g is acceleration due to gravity (9.8
m/s2), Q is discharge (m3/s), and S is the channel slope.
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13. Assignment: Different types of cross sections observed in nature
Which type will form
turbulent flow?
Which type has lowest
depth?
Which type has maximum
velocity?
Which type shows
meandering cross
section?
Which type of section
must be hilly areas?19-07-2020 LMT 13

14. Thank you
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