Dam outlet works lecture 2

ENERGY DISSIPATORS
17/2/2014 1
PREPARED BY V.H.
KHOKHANI,ASSISTANT PROFESSOR,
DIET.

Water flowing over a spillway
acquires a lot of kinetic energy
because of the conversio of the
potential energy into kinetic
energy.
If the water flowing with such a
high velocity is discharged into the
river it will scour the river bed.
If the scour is not properly
controlled it may extend backward
and may endanger the spillway and
the dam.
17/2/2014
PREPARED BY V.H.
DIET.
2

In order to protect the channel bed
against scour, the kinetic energy of
the water should be dissipated
before it is discharged into the d/s
channel.
17/2/2014
PREPARED BY V.H.
DIET.
3

17/2/2014
PREPARED BY V.H.
DIET.
4

Commonly measures adopted
1. By developing a
hydraulic jump
2. By using different
types of buckets
17/2/2014
PREPARED BY V.H.
DIET.
5

Hydraulic Jump :
Hydraulic Jump is the sudden rise of
water that takes place when the flow
changes from supercritical flow state
to the subcritical state.
When a stream of water moving with
a high velocity and low depth (i.e.
supercritical flow) strikes another
stream of water moving with low
velocity and high depth (i.e sub-
critical flow), a sudden rise in the
surface of water takes place. This
phenomenon is called Hydraulic
jump.
17/2/2014
PREPARED BY V.H.
DIET.
6

17/2/2014
PREPARED BY V.H.
DIET.
7
High velocity water with low
depth strikes low velocity
water with high depth
Rise in
water

17/2/2014
PREPARED BY V.H.
DIET.
8
y1
y2

For different discharges q,
we can obtain different y2.
if we plot graph of these q
and y2 it is known as jump
height curve
17/2/2014
PREPARED BY V.H.
DIET.
9

For different discharges q,
we can obtain different y2’
from actual observation of
tail water depth. if we plot
graph of these q and y2’ it
is known as tail water
rating curve
17/2/2014
PREPARED BY V.H.
DIET.
10

There is five condition
governs type of energy
dissipator
17/2/2014
PREPARED BY V.H.
DIET.
11

When JHC =TWRC or both
coinside
17/2/2014
PREPARED BY V.H.
DIET.
12

17/2/2014
PREPARED BY V.H.
DIET.
13

This is the stable condition
Jump will ocurrs at toe of dam
Simple horizontal filter is provided
with small rise
17/2/2014
PREPARED BY V.H.
DIET.
14

17/2/2014
PREPARED BY V.H.
DIET.
15

17/2/2014
PREPARED BY V.H.
DIET.
16

Provide ski jump
Provide sloping apron below bed
Provide subsidary dam with baffle
wall
17/2/2014
PREPARED BY V.H.
DIET.
17

17/2/2014
PREPARED BY V.H.
DIET.
18

17/2/2014
PREPARED BY V.H.
DIET.
19

17/2/2014
PREPARED BY V.H.
DIET.
20

17/2/2014
PREPARED BY V.H.
DIET.
21

Provide sloping apron such that
jump will ocurrs on apron
Roller bucket
17/2/2014
PREPARED BY V.H.
DIET.
22

17/2/2014
PREPARED BY V.H.
DIET.
23

Sloping apron with stilling basin
Sloping apron partially above
partially below river bed
17/2/2014
PREPARED BY V.H.
DIET.
24

Dam outlet works lecture 2

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Dam outlet works lecture 2