OCF Flashcards
What is the different between Rigid and
Mobile Boundary channel?
These channels are those in which the boundary
is not deformable. The shape and roughness
factor is not a function of flow parameter. Mobile
channels are those in which the boundaries
undergo deformation due to the continuous
process of erosion and deposition due to flow.
What Is prismatic and non prismatic channel?
Channels in which the cross sectional shape,
size and the bed slope are constant is termed
as Prismatic channel Natural channels generally
have varying cross section and consequently
are known a Nonprismatic channels.
What do you understand by the most
economical section of a channel?
Maximum discharge for a given cross~ sectional
area.
What Is the normal depth & critical depth of
a flow?
The noonal depth is associated with uniform flow
in a channel. The depth of flow at which the
specific energy is minimum is called critical
depth.
In what ways the open channel flow is
different from the flow in closed conduits?
In open channel, flow occurs under atmospheric
pressure and the component of weight along
the direction of slope provides the driving force
for flow in channels.
In closed conduits, flow occurs above
atmospheric pressure and difference of pressure
along the pipe i.e. pressure gradient provides
the driving force for flow in pipes. Partially full
conduits behave like open channels only.
What Is a hydraulic bore?
Hydraulic Bore: A moving hydraulic Jump is
called as “bore”. Bores can be seen on beaches
as a result of broken waves. Thus hydraulic jump
can be ·seen as the stationary wave seen in a
frame moving with the hydraulic bore.
If the Froude number of approaching flow in
an open channel is less than unity, will (a) a
decrease in channel width and (b) an
increase in its bottom elevation cause the
water surface to rise or fall?
Froude number less than unity implies subcritical flow. If the channel bottom level is
increased, then in sub-critical flow, the flow
depth will decrease. Similarly, if width of the
channel is reduced then for sub-critical flow,
the flow depth will increase.
Explain the Interaction between flow and
alluvial boundaries of an open channel
Channel flow in alluvial soils: Water moVing
with a given velocity and at a certain depth can
carry in suspension only certain amount of Stlt
of specific nature. If this water is not fully loaded
with silt then it will scour the bed and channel
boundaries (if unlined) till it gets fully loaded
with the amount of silt that it can carry. Hence
bed and banks are susceptible to erosion.
Similarly if the flowing water is having excess.
silt then it is likely to be dropped which gets
deposited at the bed and boundaries. Silting
and scouring must be prevented to have a
definite channel regime. Scouring lowers theful
supply level and reduces the command.lt may
also lead to scouring of foundation of hydraulic
structures.
Similarly silting hinders the normal functioning
of a channel. Most of the rivers of North India
flow in alluvial soils.
What do you understand by the back water
effect and afflux?
Backwater Effect: When water flowing in a river
or a canal is obstructed by construction of a
weir or barrage or dam then the depth of flow
rises above the normal flow depth. The length
of the backwater curve is the distance from the
weir or barrage or dam upstream till the normal
depth of flow is established.
Afflux: It is the rise or heading up of water
upstream of the obstruction like weir. darn.
barrage etc
What is super critical and sub critical floW?
If depth of flow in a channel is greater than tht
critical depth or Froude number < 1.0 the floW
is said sub- c ritical or streaming flow.
If depth of flow < critical depth –) super c~iti081 ·
or shooting flow and Froude number> 1.0
What is condition of maximum velocity and
discharge through a circular channel?
If Depth of flow, d = 0.81 x dia of circular chan~
then max. velocity will occur.
If depth, if d = 0 .95 x d ia of circular channel
then maximum discharge will occur.
Which is best section for open channel flow?
ESE 2009
Theoretically circular channel section gives the
minimum wetted perimeter for a given cross
sectional area and hence it is the most efficient
channel section.
Practically trapezoidal sections with curved
bottom corners are used as efficient channel
sections.
Hydraulic mean depth and flow measuring
Instrument.
Hydraulic mean depth Is the ratio of wetted area to wetted perimeter. A Hydraulic mean depth (D) = P Notches and weirs are used for the flow measurement at any section.
What can be the advantage if you transport
water via pipeline Instead of canal?
(ESE 2016)
When water is transported through pipeline then
it is under pressure. This makes possible the
transportation of fluid from lower level to higher
level which is otherwise not possible with
channel flow.
Carrying water through pipes make possible
the transportation of water across ground
depressions.
