ENERGY DISSIPATORS stilling basin A stilling basin is defined as a structure in which a hydraulic jump used for energy dissipation is confined either partly or entirely. Certain auxiliary devices such as chute blocks, sills, baffle walls, etc. are usually provided in the stilling basins to reduce the length of the jump and thus to reduce the length and the cost of the stilling basin. Moreover, these devices also improve the dissipation action of the basin and stabilize the jump. Chute Blocks : These are triangular blocks with their top surface horizontal. These are installed at the toe of the spillway just at upstream end of the stilling basin. They act as a serrated device at the entrance to the stilling basin. They furrow the incoming jet and lift a portion of it ab0ve the floor. These blocks stabilise the jump and thus improve its performance, these also decrease the length of the hydraulic jump. Basin Blocks or Baffle Blocks or Baffle Piers : These are installed on the stilling basin floor between chute blocks and the end sill. These blocks also stabilise the formation of the jump. Moreover, they increase the turbulence and assist in the dissipation of energy. They help in breaking the flow and dissipate energy mostly by impact. These baffle blocks are sometimes called friction blocks. Sills and Dentated Sills : Sill or more preferably dentated sill is generally provided at the end of the stilling basin. The dentated sill diffuses the residual portion of the high velocity jet reaching the end of the basin. They, therefore, help in dissipating residual energy and to reduce the length of the jump or the basin. particular location of these blocks mainly depends upon the initial Froude number (F1) and the velocityof the incoming flow. The stilling basins are usually rectangular in plan. These aremade up of concrete. [A] U.S.B.R. Stilling basins : [B] Indian Standards Basins : 1. Horizontal apron - Type-I 2. Horizontal apron - Type-II 3. Sloping apron - Type-Ill 4. Sloping apron - Type-IV Type I basin (F1 between 2.5 to 4.5) Provide chute blocks and end sill Length of basin = 4.3 y2 to 6.0 y2 Width of chute block = y1 Spacing = 2.5 y1 Height of chute block = 2y1 Length of chutes = 2y1 U.S.B.R. Type-II basin for F1 greater than 4.5 and v1 less than 15 m/sec.: U.S.B.R. Type-Ill basin for F, greater than 4.5 and V1 greater than 15 m/sec : Chutes and dentated sills provided Baffle is not provided because of –velocity is high and cavitation is possible. [B] Indian Standards Basins : 1. Horizontal apron - Type-I 2. Horizontal apron - Type-II 3. Sloping apron - Type-Ill 4. Sloping apron - Type-IV 1. Horizontal apron - Type-I 2. Horizontal apron - Type-II 3. Sloping apron - Type-Ill 4. Sloping apron - Type-IV 1. Horizontal apron - Type-I 2. Horizontal apron - Type-II 3. Sloping apron - Type-Ill 4. Sloping apron - Type-IV IS Type-Ill basin is usually provided with a sloping apron for the entire len

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

15. Arrange
ments
Height Width Length Locatio
n
spacing
s
Chutes
(1)
2Y1 Y1 2Y1 At toe 2.5 Y1
Baffel (3) NA NA NA NA NA
End sills
(4)
1.2 to 3 y1 2 in 1
slope
Througho
ut
spillway
section
At the
end of
basin
NA

18. Arrange
ments
Height Width Length Locatio
n
spacing
s
Chutes
(1)
Y1 Y1 2Y1 At toe y1
Baffel (3) 1.5 to 3.3
Y1
0.75 h3 2.3 TO
2.8 y1
0.8 y2
from toe
0.75 h3
End sills
(4)
1.2 to 3 y1 2 in 1
slope
Througho
ut
spillway
section
At the
end of
basin
NA

22. Arrange
ments
Height Width Length Locatio
n
spacing
s
Chutes
(1)
Y1 Y1 2Y1 At toe y1
Baffel (3) NA NA NA NA NA
End sills
DENTAT
ED END
SILLS (4)
O.2 Y2 0.02 Y2 0.15 Y2 At the
end of
basin
NA0.15
Y2

25. USBR
TYPES
FR NO VELOCIT
Y
PROVISI
ONS
I 2.5 TO 4.5 NA CHUTES END SILL
II MORE
THAN 4.5
LESS
THAN 15
CHUTES BAFFLE
END SILL
III MORE
THAN 4.5
MORE
THAN 15
CHUTES DENTATE
D SILL

27. Arrange
ments
Height Width Length Locatio
n
spacing
s
Chutes
(1)
2Y1 Y1 2Y1 At toe 2.5 y1
Baffel/ba
sin blocks
(3)
0.8 to
3.3 Y1
0.02 y1 Height of
blocks
0.8 y2
from toe
Height of
blocks
Dentated
sills (4)
0.20 y2 0.02 y2 Height of
sills
At the
end of
basin
Height of
sills