Table Of Contentइंटरनेट मानक
Disclosure to Promote the Right To Information
Whereas the Parliament of India has set out to provide a practical regime of right to
information for citizens to secure access to information under the control of public authorities,
in order to promote transparency and accountability in the working of every public authority,
and whereas the attached publication of the Bureau of Indian Standards is of particular interest
to the public, particularly disadvantaged communities and those engaged in the pursuit of
education and knowledge, the attached public safety standard is made available to promote the
timely dissemination of this information in an accurate manner to the public.
“जान1 का अ+धकार, जी1 का अ+धकार” “प0रा1 को छोड न’ 5 तरफ”
Mazdoor Kisan Shakti Sangathan Jawaharlal Nehru
“The Right to Information, The Right to Live” “Step Out From the Old to the New”
IS 7365 (2010): Criteria for hydraulic design of bucket
type energy dissipators [WRD 9: Dams and Spillways]
“!ान $ एक न’ भारत का +नम-ण”
Satyanarayan Gangaram Pitroda
““IInnvveenntt aa NNeeww IInnddiiaa UUssiinngg KKnnoowwlleeddggee””
“!ान एक ऐसा खजाना > जो कभी च0राया नहB जा सकता हहहहै””ै”
Bhartṛhari—Nītiśatakam
“Knowledge is such a treasure which cannot be stolen”
IS 7365: 2010
Hkkjrh; ekud
ckYVh Vkbi mtkZ {k;dkjdksa dh nzopkfyr
fMtkbu ds ekin.M
(nwljk iqujh{k.k )
Indian Standard
CRITERIA FOR HYDRAULIC DESIGN OF BUCKET TYPE
ENERGY DISSIPATORS
( Second Revision )
ICS 93.16
4
6
_
9
0
© BIS 2010 0
2
S:
B U R E A U O F I N D I A N S T A N D A R D S C
HI
MANAK BHAVAN, 9 BAHADUR SHAH ZAFAR MARG P
A
NEW DELHI 110002 GR
E
N
HI
S
N
March 2010 Price Group 11 U
S
Dams and Spillways Sectional Committee, WRD 9
FOREWORD
This Indian Standard (Second Revision) was adopted by the Bureau of Indian Standards, after the draft finalized
by the Dams and Spillways Sectional Committee had been approved by the Water Resources Division Council.
This standard was first published in 1974. The first revision was taken up in 1985 to reflect the latest practices
prevailing and to utilize the knowledge gained during the use of the standard. This revision has been taken up to
utilize the experience further gained during the use of this standard.
Energy dissipator at the toe of spillway of a hydraulic structure is necessary to minimize erosion of strata
downstream of the structure. For this purpose there are different types of energy dissipators, such as hydraulic
jump, impact, jet diffusion, interacting jets, hollow jet and multiple ski-jump. Generally bucket type energy
dissipators are being used for energy dissipation in medium and high dams.
Hydraulic behaviour of bucket type energy dissipator depends on dissipation of energy through:
a) interaction of two rollers formed, one in the bucket, rolling anti-clockwise (if the flow is from the left to
the right) and the other downstream of the bucket, rolling clockwise; or
b) interaction of the jet of water, shooting out from the bucket lip, with the surrounding air and its impact
on the channel bed downstream.
Bucket type energy dissipators can be either:
a) roller bucket type energy dissipator, or
b) trajectory bucket type energy dissipator.
For the purpose of deciding whether a particular requirement of this standard is complied with, the final value,
observed or calculated expressing the result of a test or analysis, shall be rounded off in accordance with IS2:1960
‘Rules for rounding off numerical values (revised)’. The number of significant places retained in the rounded off
value should be the same as that of the specified value in this standard.
IS 7365 : 2010
Indian Standard
CRITERIA FOR HYDRAULIC DESIGN OF BUCKET TYPE
ENERGY DISSIPATORS
( Second Revision )
1 SCOPE b) interaction between the jet and surrounding air,
c) diffusion of the jet in the tailwater,
This standard lays down criteria for hydraulic design
of bucket type energy dissipators. d) impact of the channel bed, and
e) pre-formed plunge pool.
2 TERMINOLOGY
3 SYMBOLS
For the purpose of this standard the following
definitions shall apply. The symbols used in the standard are defined as given
below:
2.1 Solid Roller Bucket — An upturn solid bucket
(see Fig. 1A) is used when the tailwater depth is much a = vertical distance from the lip level to the
in excess of sequent depth and in which dissipiation of highest point of the centre of jet, in m;
considerable portion of energy occurs as a result of
d = critical depth, in m;
c
formation of two complementary elliptical rollers, one
d = depth of scour below tailwater level, in m;
in bucket proper, called a surface roller, which is anti- s
clockwise (if the flow is from the left to the right) and Ds = horizontal distance from spillway crest axis to
the other downstream of the bucket, called the ground the point of maximum probable scour, inm;
roller, which is clockwise. d = depth of flow entering bucket, in m;
1
2.2 Slotted Roller Bucket — An upturn bucket with d2 = sequent depth, in m;
teeth in it (see Fig. 1B) is used when the tailwater depth d = height of tailwater above bucket invert, inm;
3
is much in excess of sequent depth and in which the
d = tailwater level minus bucket lip elevation,
4
dissipation of energy occurs by lateral spreading of jet
in m;
passing through bucket slots in addition to the
F = Froude number of jet entering bucket;
formation of two complementary rollers as in the solid j
bucket. v
= a
2.3 Trajectory Bucket/Flip Bucket — An upturn solid gd1
bucket (see Fig. 1C) is used when the tailwater depth F = discharge parameter;
D
is insufficient for the formation of the hydraulic jump,
q
the bed of the river channel downstream comprises = · 103
sound rock and is capable of withstanding, without gH3/2
1
excessive scour, the impact of the high velocity jet.
g = acceleration due to gravity, in m/s2;
The flow coming down the spillway is thrown away
h = height of roller above bucket invert, in m;
from toe of the dam to a considerable distance b
downstream as a free discharging upturned jet which h = height of surge above bucket invert, in m;
s
falls into the channel directly, thereby avoiding H = depth of overflow over spillway, in m;
excessive scour immediately downstream of the
H = reservoir pool elevation minus bucket invert
spillway. There is hardly any energy dissipation within 1
elevation, in m;
the bucket itself. The device is used mainly to increase
the distance from the structure to the place where high H2 = spillway crest elevation minus bucket invert
velocity jet hits the channel bed, thus avoiding the elevation, in m;
danger of excessive scour immediately downstream of H = reservoir pool elevation minus tailwater
3
the spillway. Due to the throw of the jet in the shape of elevation, in m;
a trajectory, energy dissipation takes place by: H = reservoir pool elevation minus bucket lip
4
a) internal friction within the jet, elevation, in m;
1
IS 7365 : 2010
H = reservoir pool elevation minus jet surface S = horizontal distance from spillway crest axis
5 d
elevation on bucket, in m; of the point of maximum probable surge, inm;
H = velocity head of jet at bucket lip, in m; T = maximum tailwater depth, above bucket
v Max
P = pressure on the bucket, in t/m2; invert, for good performance of slotted roller
bucket, in m;
q = discharge intensity per metre of bucket
width, in [m3/s]/m; TMin= minimum tailwater depth, above bucket
invert, for good performance of slotted roller
Q = total discharge, in m3/s;
bucket, in m;
R = radius of bucket, in m;
1A SOLID ROLLER BUCKET
1B SLOTTED ROLLER BUCKET
1C TRAJECTORY BUCKET
FIG. 1 SKETCHES FOR BUCKET TYPE ENERGY DISSIPATORS
2
IS 7365 : 2010
T = tailwater sweep out depth, in m; 4.1.1.2 In the case of slotted roller bucket, a part of the
s
v = actual velocity of flow entering bucket, in m/s; flow passes through the slots, spreads laterally and is
a
lifted away from the channel bottom by a short apron
v = theoretical velocity of flow entering bucket,
t at the downstream end of the bucket. Thus the flow is
in m/s;
dispersed and distributed over a greater area resulting
X = horizontal throw distance from bucket lip
in a less violent ground roller. The height of boil is
to the centre point of impact with tailwater,
also reduced in case of slotted roller bucket. The slotted
in m;
bucket provides a self-cleaning action to reduce
Y = difference between the lip level and abrasion in the bucket.
tailwater, sign taken as positive for tailwater
4.1.1.3 In general the slotted roller bucket is an
below the lip level and negative for tailwater
improvement over the solid roller bucket for the range
above the lip level, in m;
of tailwater depths under which it can operate without
g = specific weight of water, in t/m3; and
sweep out or diving. However, it is necessary that
= bucket lip angle (exit angle) with horizontal, specific model experiments should be conducted to
f
in degree. verify pressure on the teeth so as to avoid cavitation
conditions. In case of hydraulic structures, slotted roller
4 HYDRAULIC DESIGN OF ROLLER BUCKET
buckets should not be provided where heavy sediment/
TYPE ENERGY DISSIPATORS (SOLID AND
gravel/boulder are expected. Heavy sediment load/
SLOTTED ROLLER BUCKETS)
gravel/boulders rolling down the spillway face can
cause heavy damage to the teeth thereby making them
4.1 General
ineffective and on the contrary, increasing the chances
4.1.1 The following two types of roller buckets are of damage by impact, cavitation and erosion.
adopted on the basis of tailwater conditions and
4.1.2 Drawal of Bed Materials
importance of the structure:
A major problem with the solid roller bucket would be
a) Solid roller bucket, and
the damage caused to the bucket due to churning action,
b) Slotted roller bucket.
because of the downstream bed material brought into
Roller bucket type energy dissipator is preferred when; the bucket by the pronounced ground roller. Even in a
slotted roller bucket, downstream material might get
a) tailwater depth is high (greater than 1.1 times
drawn due to unequal operation of gates. The channel
sequent depth preferably 1.2 times sequent
bed immediately downstream of the bucket shall be
depth), and
set at 1 to 1.5 m below the lip level to minimize the
b) river bed rock is sound. possibility of this condition. Where the invert of the
bucket is required to be set below the channel general
4.1.1.1 In the case of solid roller bucket, the ground
bed level, the channel should be dressed down in one
roller is more pronounced. It picks up material from
level to about 1 to 1.5 m below the lip level for
downstream bed and carries it towards the bucket where
about15m length downstream and then a recovery
it is partly deposited and partly carried away
slope of about 3 (horizontal) to 1 (vertical) should be
downstream by the residual jet from the lip. The
given to meet the general bed level as shown in Fig. 2.
deposition in roller bucket is more likely when the
Model studies should be done to check this tendency.
spillway spans are not operated equally, setting up
If possible, even provision of properly anchored solid
horizontal eddies downstream of the bucket. The picked
concrete apron laid on fresh rock may be considered
up material which is drawn into the bucket can cause
to avoid river bed material drawing into the bucket, as
abrasive damage to the bucket by churning action.
FIG. 2 RECOVERY SLOPE DOWNSTREAM OF SOLID ROLLER BUCKET
3
IS 7365 : 2010
it may cause heavy erosion on the spillway face, bucket hydraulic phenomenon of sweep out or heavy
and side training walls. submergence occurs depending upon which of the
rollers is inhibited.
4.1.2.1 In the case where the bucket invert is
substantially higher than the general channel bed level 4.2.2 Design Criteria
and the channel bed is erodible, the cascading flow
The principal features of hydraulic design of solid roller
over the lip for small discharges may cause deep scour
bucket consists of determining;
very close to the bucket lip. A concrete apron of width
15 m or more if required may be provided downstream a) bucket invert elevation,
and parallel to the end sill as shown in Fig. 3 to b) radius of the bucket, and
minimize the possible scour in the bed near the bucket
c) slope of the bucket lip or the bucket lip angle.
lip. The apron should be keyed into good rock.
4.2.2.1 Bucket invert elevation
4.1.3 Precautions in Operation
Normally the invert level of a roller bucket is so fixed
It is necessary to operate all the spillways gates equally
that the difference in the maximum tailwater level
(under partial operation condition) to achieve
corresponding to design flood and the invert level (d )
satisfactory performance of the bucket. Unsymmetrical 3
is between 1.1 to 1.4 times the sequent depth (d ). Thus
operation of gates or operation of only a few gates at a 2
d = 1.1 to 1.4 times d . The design charts given in
time may set up horizontal eddies in the channel 3 2
Fig.4 and Fig. 5 and sample calculations given in
downstream which may bring debris into the bucket.
Annex A may be used to determine the bucket invert
All loose debris inside and just beyond the bucket
elevation and probable roller and surge height for the
should be removed after construction and before the
expected range of spillway discharges. Satisfactory
bucket is put to use.
energy dissipation is obtained when the roller height
4.1.3.1 Divide walls would be necessary to segregate (h ) is between 75 and 90 percent of the tailwater depth
b
the spillway spans, if unequal spillway operations (d ). If the aforesaid two criteria are satisfied, then the
3
cannot be avoided with due consideration for building surge height (h) measured above the invert level is105
s
of tailwater level for various discharges. Also when to 130 percent of the tailwater d , that is, h/d = 1.05
3 s 3
the invert levels of the buckets in adjacent bays are to 1.3. When the invert elevation arrived at to get the
provided at different elevations, divide walls may be h /d ratio between 0.75 and 0.90, is considerably
b 3
required depending upon the flow conditions. Model below the channel bed level, substantial excavation
studies may be conducted for such cases. The divide would be involved for dressing downstream channel
walls shall be designed for unequal operation condition bed down to 1.0 to 1.5 m below the endsill level in
of the spillway spans and also for differential pressure minimum 15.0 m length or more in the downstream
due to adjoining gates closed on one side and all gates depending upon the discharge intensity and the head.
open on the other side. It would, therefore, be preferable if the invert level can
be brought near to the channel bed level with the h /d
b 3
4.2 Hydraulic Design of Solid Roller Bucket ratio still remaining within the prescribed limits, and
d being about 1.2 to 1.4 times d . The charts are
4.2.1 General 3 2
applicable for the ranges of variables shown in Fig. 4
For effective energy dissipation in a solid roller bucket and Fig. 5. The channel bed elevation is believed to
both the surface or dissipating roller and the ground or have negligible effect on roller and surge heights.
stabilizing roller should be well formed, otherwise
FIG. 3 CONCRETE APRON LAID ON FRESH ROCK
4
IS 7365 : 2010
RANGE OF H/R FOR SATISFACTORY
1
PERFORMANCE OF BUCKET
q Equivalent Range of
gH3/2 F H/R
1 1
0.090 5.4 2 to 5
0.060 6.7 2 to 6
0.040 8.3 2 to 6
0.026 10.3 3 to 6
0.013 14.7 3 to 8
Range of variables:
Spillway slopes (S : 1) 1 : 1 to 1.67 : a
Lip angle (f ) =45° [the curves may
also be used for other
lip angles (see 4.2.2.3)]
H/H =0.68 to 0.93
2 1
FIG. 4 DESIGN OF SOLID ROLLER BUCKET — ROLLER DEPTH
5
