H&i Notes

Dr.H.S.Govardhana Swamy , Head of Civil Engineering Department .
MODULE 1: GRAVITY DAMS
A dam is a hydraulic structure built across a river. Gravity dams are massive in construction.
The forces acting on the dam are resisted by its massive weight.
Classification of Dams
Dams can be classified according to different criteria, as given below:
(a) Based on Function Served:
1. Storage dams: Storage (or conservation) dams are constructed to store water during the rainy
season when there is a large flow in the river. The stored water is utilized later during the period
when the flow in the river is reduced and is less than the demand.
2. Detention dams: Detention dams are constructed for flood control. A detention dam retards
the flow in the river on its downstream during floods by storing some flood water. The water
retained in the reservoir is later released gradually at a controlled rate according to the carrying
capacity of the channel downstream of the detention dam.
3. Diversion dams: A diversion dam is constructed for the purpose of diverting water of
the river into an off-taking canal (or a conduit).
4. Debris dams: A debris dam is constructed to retain debris such as sand, gravel, and
RajaRajeswari College of Engineering / 9663736535

Dr.H.S.Govardhana Swamy , Head of Civil Engineering Department . 2
drift wood flowing in the river with water.
(b) Based on Hydraulic Design: On the basis of hydraulic design, dams may be classified as
1. Overflow dams:
surplus water which cannot be retained in the reservoir is permitted to pass over the crest of the
overflow dam which acts as a spillway Most of the gravity dams have overflow sections for some
length and the rest of the length as a non-overflow dam. The overflow dam is also called the
spillway section
2. Non-overflow dams: a non-overflow dam can be built of any material, such as concrete,
masonry, earth, rockfill and timber. As already mentioned, the non-overflow dam is usually
provided in a part of the total length of the dam.
(c) Based on Materials of Construction: Based on the materials used in construction, the dams
are classified as follows: (1) Masonry dam, (2) Concrete dam, (3) Earth dam, (4) Rockfill dam,
(5) Timber dam, (6) Steel dam, (7) Combined concrete-cum-earth dam, and (8) Composite dam.
(d) Based on Rigidity: On the basis of the rigidity, the dams are classified into 2 types:
1. Rigid dams: It is constructed of stiff materials such as concrete, masonry, steel and
timber. These dams deflect and deform very little when subjected to water pressure and other
forces.
2. Non-rigid dams: A non-rigid dam is relatively less stiff compared to a rigid dam. The dams
constructed of earth and rockfill are non-rigid dams. There are relatively large settlements and
deformations in a non-rigid dam.Rockfill dams are actually neither fully rigid nor fully non-rigid.
These are sometimes classified as semirigid dams.
(e) Based on the structural action:

This is the most commonly used classification of dams. Based on the structural action,
the dams are classified as
(1) Gravity dams,
(2) Earth dams,
(3) Rock fill dams,
(4) Arch dams,
(5) Buttress dams,
(6) Steel dams,
1. Gravity dams: A gravity dam resists the water pressure and other forces due to its weight.Thus
the stability of a gravity dam depends upon its weight. The gravity dams are usually made of
cement concrete.

Advantages
(i) Gravity dams are quite strong, stable and durable.
(ii) Gravity dams are quite suitable across moderately wide valleys and gorges having
steep slopes where earth dams, if constructed, might slip.
(iii)Gravity dams can be constructed to very great heights, provided good rock
foundations are available.
(iv) Gravity dams are well adapted for use as an overflow spillway section. Earth dams
cannot be used as an overflow section. Even in earth dams, the overflow section is
usually a gravity dam.
(v) Gravity dams are specially suited to such areas where there is very heavy
downpour.The slopes of the earth dams might be washed away in such an area.
(vi) The maintenance cost of a gravity dam is very low.
(vii) The gravity dam does not fail suddenly. There is enough warning of the imminent
failure and the valuable property and human life can be saved to some extent.
(viii) Gravity dam can be constructed during all types of climatic conditions.
(ix) The sedimentation in the reservoir on the upstream of a gravity dam can be
somewhat reduced by operation of deep-set sluices.
Disadvantages
(i) Gravity dams of great height can be constructed only on sound rock foundations.
These cannot be constructed on weak or permeable foundations on which earth
Dams can be constructed. However, gravity dams upto 20 m height can be
constructed
even when the foundation is weak.
(ii) The initial cost of a gravity dam is usually more than that of an earth dam. At the
sites where good earth is available for construction and funds are limited, earth dams
are better.
(iii)Gravity dams usually take a longer time in construction than earth dams, especially
when mechanised plants for batching, mixing and transporting concrete are not
available.
(iv) Gravity dams require more skilled labour than that in earth dams.
(v) Subsequent raising is not possible in a gravity dam.

Forces Acting on Gravity Dam
A gravity dam is subjected to the following main forces:
1. Weight of the dam 2. Water pressure 3. Uplift pressure 4. Wave pressure 5. Silt pressure 6. Ice
pressure 7. Wind pressure 8. Earthquake forces
These forces fall into two categories as: a) Forces, such as weight of the dam and water
pressure, which are directly calculable from the unit weights of the materials and properties of
fluid pressures; and b) Forces, such as uplift, earthquake loads, silt pressure and ice pressure,
which can only be assumed on the basis of assumption of varying degree of reliability. It is
convenient to compute all the forces per unit length of the dam.
1. Weight of the dam
The weight of the dam is the main stabilizing force in a gravity dam. The weight of the dam per
unit length is equal to the product of the area of cross-section of the dam and the specific weight
(or unit weight) of the material. The specific weight of the concrete is usually taken as 24 kN/m3,
and that of masonry as 23 kN/m3.For convenience, the cross-section of the dam is divided into
simple geometrical shapes, such as rectangles and triangles, for the computation of weights. The
areas and centroids of these shapes can be easily determined. Thus the weight components W1,
W2, W3 etc. can be found along with their lines of action. The total weight W of the dam acts at
the C.G. of its section.
2. Reservoir and Tail water loads (Water pressure)
The water pressure acts on the upstream and downstream faces of the dam. The water pressure on
the upstream face is the main destabilizing (or overturning) force acting on a gravity dam. The tail
water pressure helps in the stability. The mass of water is taken as 1000 kg/m 3. The water
pressure intensity p (kN/m2) varies linearly with the depth of the water measured below the free
surface y (m) and is expressed as p = γw h2 where γw is the specific weight of water (=9.81 kN/m3).
The water pressure always acts normal to the surface. While computing the forces due to water
pressure on inclined surface, it is convenient to determine the components of the forces in the
horizontal and vertical directions.
U/s face vertical: When the upstream face of the dam is vertical, the water pressure diagram is
triangular in shape with a pressure intensity of γwh at the base, where h is the depth of water. The
total water pressure per unit length is horizontal and is given by
p = γw h2
It acts horizontally at a height of h/3 above the base of the dam.

(U/s face inclined: When the upstream face ABC is either inclined or partly vertical and partly
inclined, the force due to water pressure can be calculated in terms of the horizontal component
PH and the vertical component PV. The horizontal component acts horizontal at a height of (h/3)
above the base. The vertical component PV of water pressure per unit length is equal to the weight
of the water in the prism ABCD per unit length. For convenience, the weight of water is found in
two parts PV1 and PV2 by dividing the trapezium ABCD into a rectangle BCDE and a triangle ABE.
Thus the vertical component PV = PV1 + PV2 = weight of water in BCDE + weight of water in ABE.
The lines of action of PV1 and PV2 will pass through the respective centroids of the rectangle and
triangle.
3. Uplift pressure
Water has a tendency to seep through the foundation, joints between the body of the dam and its
foundation at the base, and through the body of the dam. The seeping water exerts pressure and
must be accounted in the stability calculations. The uplift pressure is defined as the upward
pressure of water as it flows or seeps through the body of the dam or its foundation.

Silt Pressures
IS code recommends that a) Horizontal silt and water pressure is assumed to be equivalent to that
of a fluid with a mass of 1360 kg/m3, and b) Vertical silt and water pressure is determined as if
silt and water together have a density of 1925 kg/m3.
Wave Pressure
In addition to the static water loads the upper portions of dams are subject to the impact of waves.
The force of waves depend mainly on the extent of the water surface, the velocity of wind and the
depth of reservoir water. The wave pressure diagrams can be approximately represented by the
triangle l-2-3 as in Fig below.

Elementary Profile of a Gravity Dam
In the absence of any force other than the forces due to water, an elementary profile will be
triangular in section, having zero width at the water level, where water pressure is zero, and a
maximum base width b, where the maximum water pressure acts. For reservoir empty condition,
a right angled triangular profile will provide the maximum possible stabilizing force against
overturning, without causing tension in the base. The main three forces considered are weight of
the dam, water pressure, and uplift pressure acting on the elementary profile of a gravity dam.

Base width of the elementary profile
The base width of the elementary profile can be found under two criteria: (1) No Tensile
Stress (2) No Sliding
No Tensile Stress Criterion: when reservoir is empty, for no tension to develop, the resultant
should act at the inner third point. For the reservoir full condition, for no tension to develop, the
resultant R must pass through the outer third point. Taking the moment of all forces about M2 and
equating it to zero we get,
Practical Profile of a Gravity Dam

The elementary profile of a gravity dam is triangular in shape, having zero width at the top.
The elementary profile of the gravity dam is only a theoretical profile. However such a
profile is not possible in practice because of the provision of (i) top width or roadway at the
top, (ii) additional loads due to the roadway, and (iii) freeboard. Fig. shows the dimensions of
the practical profile of a gravity dam.

Galleries:
A gallery is a opening left in a dam. This run in transverse or longitudinal direction The shape
and size varies from dam to dam and is generally governed by the functions it has to perform.
Following are the purposes for which a gallery is formed in the dams.
1. To provide drainage' of the dam section. Some amount of water constantly seeps through the
upstream face of the dam which is drained off through galleries.
2. To provide facilities for drilling and grouting operations for foundations etc. Drillings for
drain is generally resorted to clean them if they are clogged. High pressure
grouting and required drilling for it is generally carried out after the completion of
dam. This can be best done through galleries.
3. To provide space for header and return pipes for post cooling of concrete and grouting
the longitudinal joints after completion of dam.
4. To provide access to observe and measure the behavior of the structure after its completion by
fixing thermocouples and examining development of cracks etc.
5. To provide an access of mechanical contrivances needed for the operation of outlet gates and
spillway gates.
Safety Criteria
Safety against Overturning
If the resultant of all the forces acting on a dam passes outside the base, the dam would
overturn. Since the dam is usually designed on no tension basis, it follows that the resultant
should pass through the middle third. If other safety criteria like maximum compressive
stresses and sliding are also fulfilled, then usually a factor of safety between 1.5 to 2.5 is
available against overturning. Factor of safety against overturning may be defined as the ratio
of the stabilizing moments to the overturning moments about the toe of the dam.
Safety against Sliding
In order that the dam may not slide the total forces tending to slide the dam should not exceed
a certain ratio Expressing mathematically H/V < µ, where µ is the coefficient of friction.
The safe value of ' µ ' is usually taken up to 0.75.In certain cases this value, under abnormal
loading conditions, becomes more than 0.75. When ' µ, becomes more than 0.75, the shear
friction factor may be calculated.

MODULE 2 : EARTH DAMS
INTRODUCTION
Earth dams have been built for the storage of water for irrigation since the
earliest times. These dams were however, limited in height. Earth dams are
constructed basically using earth material.
Classification of Earth Dams:
Earth dams are classified as follows:
1) Based on method of construction :

a) Rolled fill earth dam
b) Hydraulic fill earth dam
2) Based upon section of the dam :
a) Homogeneous earth dam
b) Zoned earth dam
c) Diaphragm type earth dam
Rolled fill earth dam: In this type of dam, successive layers of soil are laid one
over the other of thickness about 15 cm- 30cm.The layers are compacted by
using rollers. Once the layer is fully compacted, next layer is laid and
compacted. This type of construction gives more stability and imperviousness
and hence this method is popular and commonly used
Hydraulic fill earth dam: In type of dam, excavation, transportation and

construction is done using hydraulic methods. Mixture of soil materials in slurry
condition is pumped and discharged in to the place where construction of dam is
carried out. No compaction is done here. The soil mixture settles gradually once
the saturation is dried. This method of construction leads the development of
pore pressures and shrinkage effects. This method is almost outdated nowadays.

Homogeneous earth dam: Constructed with uniform and homogeneous

material and is suitable for low height dams. The u/s face is relatively flatter
compares to the d/sface.Percolation of water is most common in earth dam, this
can be prevented by providing stone revetments on u/s face and at the d/s toe
A fully homogeneous section might be found convenient where the slopes are required to be
flat because of a weak foundation, although even in this case some drainage measures may be
necessary. The modified homogeneous type of embankment is most suitable in localities
where readily available soils show practically no variation in permeability.
Zoned earth dam : These are also known as non homogeneous earth dams. The
central portion of the dam, known as core is made-up of impervious material
and made watertight to prevent the leakage of water through the body of dam.
The cross section of the core is trapezoidal and can be constructed using puddle
clay or concrete or masonry.Cutooff walls may also provide to check the
seepage.
Diaphragm type earth dam: This type of dam is constructed using pervious
materials with a thin impervious diaphragm at the centre portion of the dam to

prevent the leakage of water. The diaphragm can be constructed using puddle
clay or concrete or masonry
.
.
Failure of Earth Dams:
Like other hydraulic structures earth dams are also subjected to failures due to
faulty design, improper construction, poor maintained etc.The various causes of
failure of earth dams may be classified as follows:
1) Hydraulic failures
2) Seepage failures
3) Structural failures
Hydraulic failures: Following are the various types of hydraulic failures:
1) Overtopping :when the free board and capacity of the spillway is

insufficient the flood water may flow over the dam
2) Erosion of the d/s toe: The d/s toe may be eroded due to heavy cross
currents of water falling from the spillway also from the tail water. This can
be prevented by providing side walls to check the entry of water towards
the earth dam
3) Erosion of the u/s face: due to the action of waves generated on the u/s
side of the face, gradually the soil mass may erode resulting failure. This
type of failure can be prevented by providing stone revetment on the face.
4) Gully formation at d/s side: When the heavy rain falls on the d/s face over
longer period of time, the soil mass stars eroding and lead to the formation
of gully traps. By properly grassing the face can reduce this type of failure.

Seepage failures:
Even though the seepage is most common in case of earth dams, when the
seepage is uncontrolled seepage failure may occur in the dam.
Following are the various types of seepage failures:
1) Piping through body of the dam:
The body of dam contains pores through which water slowly starts seeping from
u/s to d/s which leads to the formation of small channels inside the body of dam
called pipes.
2) Piping through foundation of the dam:
When highly pervious material is used in the construction foundation of the

dam, allow heavy seepage into foundation which forms pipes in the
foundation
Structural failures: structural failures occur due to the sliding of soil mass.
Following are the various types of seepage failures:
1) Slide in embankment: if the side slopes of the dam is steep, the soil mass
slide gradually.
2) Foundation slide: If the foundation material is fine sediment, it may settle
vertically over longer period of time leading to the foundation slide.
3) Failure due to earthquake: The earthquake forces may destroy the whole
dam or part of the dam.The shocking waves create sliding of soil mass
4) Faulty design of the dam: If the dam is not designed as per standard design
specifications, then structural failure may occur.

Types of failures—Earth dams

Design Criteria of Earth Dams
Based on the experience of failures, the following main design criteria may be laid down for
the safety of an earth dam.
1. To prevent hydraulic failures, the dam must be so designed that erosion of the
embankment is prevented.
The conditions to be satisfied are as follows.
(a) Spillway capacity should be sufficient to pass the flood flow.

(b) Overtopping by wave action at maximum water level should be prevented.
(c) The original height of structure is sufficient to maintain the minimum safe freeboard after
settlement has occurred.
(d) Erosion of the embankment due to wave action and surface run-off does not occur.
(e) The crest should be wide enough to withstand wave action and earthquake shock.
2. To prevent the seepage failures, the flow of water through the body of the dam and its
foundation must not be sufficiently large in quantity to defeat the purpose of the
structure nor at a pressure sufficiently high to cause piping.
The conditions to be satisfied are as follows
(a) Quantity of seepage water through the dam section and foundation should be limited.
(b) The seepage line should be well within the downstream face of the dam to prevent
Sloughing.
(c) Seepage water through the dam or foundation should not remove any particle which cause
piping.
(d) There should not be any leakage of water from the upstream to downstream face. Such
leakage may occur through conduits, at joints between earth and concrete sections or through
holes made by aquatic animals.
3. To prevent structural failures, the embankment and its foundation must be stable
under all Conditions.
(i) The upstream and downstream slopes of the embankment should be stable under all
loading conditions to which they may be subjected including earthquake.
(ii) The foundation shear stresses should be within the permissible limits of shear strength of
the material.
SEEPAGE CONTROL IN EARTHEN DAMS:
If proper measures are not taken to control the seepage, water will percolate through the
embankment and through foundation. Following are some measures taken to control the
seepage in the earth dams:

Control of Seepage through Foundations
1. by providing drainage trenches.

2. by providing impervious cut-offs
3. by providing Sheet piling
4. by providing Cast in situ concrete diaphragm
5. by providing Upstream impervious blanket on u/s slope
6. by providing Pressure relief wells.
Control of Seepage through Embankments
1. by providing horizontal drainage filters.

2. by providing toe filter
3. by providing Sheet piling
4. by providing coarse section on the d/s side
5. by providing chimney drains
6. using relatively impervious material for construction of dam
SECTION OF AN EARTH DAM:

MODULE 3 : Spillways:
Introduction :
Spillways are structures constructed to provide safe release of flood waters from a dam to a
downstream are, normally the river on which the dam has been constructed. Every reservoir has a
certain capacity to store water. If the reservoir is full and flood waters enter the same, the reservoir
level will go up and may eventually result in over-topping of the dam. To avoid this situation, the
flood has to be passed to the downstream and this is done by providing a spillway which draws water
from the top of the reservoir. A spillway can be a part of the dam or separate from it. Spillways can
be controlled or uncontrolled. A controlled spillway is provided with gates which can be raised or
lowered. Controlled spillways have certain advantages as will be clear from the discussion that
follows. When a reservoir is full, its water level will be the same as the crest level of the spillway.
This is the normal reservoir level. If a flood enters the reservoir at this time, the water level will start
going up and simultaneously water will start flowing out through the spillway. The rise in water
level in the reservoir will continue for some time and so will the discharge over the spillway. After
reaching a maximum, the reservoir level will come down and eventually come back to the normal
reservoir level. The top of the dam will have to be higher than the maximum reservoir level
corresponding to the design flood for the spillway, while the effective storage available is only up to
the normal reservoir level. The storage available between the maximum reservoir level and the
normal reservoir level is called the surcharge storage and is only a temporary storage in uncontrolled
spillways. Thus for a given height of the dam, part of the storage - the surcharge storage is not being
utilized. In a controlled spillway, water can be stored even above the spillway crest level by keeping
the gates closed. The gates can be opened when a flood has to be passed.
TYPES OF SPILLWAYS –
There are different types of spillways that can be provided depending on the suitability of site and
other parameters. Generally a spillway consists of a control structure, a conveyance channel and a
terminal structure, but the former two may be combined in the same for certain types. The more
common types are briefly described below.
 Straight Drop Spillways

„ Overflow Spillways
„ Chute Spillways
„ Side Channel Spillways
„ Shaft Spillways
„ Siphon Spillways
1. OGEE SPILLWAY: The Ogee spillway is generally provided in rigid dams and forms a part of
the main dam itself if sufficient length is available. The crest of the spillway is shaped to conform to
the lower nappe of a water sheet flowing over an aerated sharp crested weir.
2. CHUTE (TROUGH) SPILLWAY In this type of spillway, the water, after flowing over a short
crest or other kind of control structure, is carried by an open channel (called the "chute" or "trough")
to the downstream side of the river. The control structure is generally normal to the conveyance
channel. The channel is constructed in excavation with stable side slopes and invariably lined. The
flow through the channel is supercritical. The spillway can be provided close to the dam or at a
suitable saddle away from the dam where site conditions permit. The chute spillway is ideally suited
with earth-fill dams because of: (i) The simplicity of their design and construction, (ii) Their
adaptability to all types of foundation ranging from solid rock to soft clay, and (iii) Overall economy
usually obtained by the use of large amounts of spillway excavation for the construction of
embankment. The chute spillway is also suitable for concrete dams constructed in narrow valleys
across a river whose bed is erodible for which ogee spillway becomes unsuitable.
3. SIDE CHANNEL SPILLWAY Side channel spillways are located just upstream and to the side
of the dam. The water after flowing over a crest enters a side channel which is nearly parallel to the
crest. This is then carried by a chute to the downstream side. Sometimes a tunnel may be used
instead of a chute.
4. SHAFT (MORNING GLORY OR GLORY HOLE) SPILLWAY This type of spillway utilizes
a crest circular in plan, the flow over which is carried by a vertical or sloping tunnel on to a
horizontal tunnel nearly at the stream bed level and eventually to the downstream side. The diversion
tunnels constructed during the dam construction can be used as the horizontal conduit in many cases.
In a shaft spillway, water enters a horizontal crest, drops through a vertical or sloping shaft and then
flows to the downstream river channel through a horizontal or nearly horizontal conduit or tunnel. A
rock outcrop projecting into the reservoir slightly upstream of the dam would be an ideal site for a
shaft spillway.
5. SIPHON SPILLWAY As the name indicates, this spillway works on the principle of a siphon. A
hood provided over a conventional spillway forms a conduit. With the rise in reservoir level water
starts flowing over the crest as in an "ogee" spillway. The flowing water however, entrains air and
once all the air in the crest area is removed, siphon action starts. Under this condition, the discharge
takes place at a much larger head. The spillway thus has a larger discharging capacity. The inlet end
of the hood is generally kept below the reservoir level to prevent floating debris from entering the
conduit. This may cause the reservoir to be drawn down below the normal level before the siphon
action breaks and therefore arrangement for de-priming the siphon at the normal reservoir level is
provided.
6. FREE OVER-FALL SPILLWAY: As the name of the spillway indicates, the flow drops freely
from the crest of a free over-fall spillway. At times, the crest is extended in the form of an
overhanging lip to direct small discharges away from the downstream face of the overflow section.
The underside of the falling water jet is properly ventilated so that the jet does not pulsate. Such a
spillway is better suited for a thin arch dam whose downstream face is nearly vertical.Since the flow
usually drops into the stream bed, objectionable scour may occur in some cases and a deep plunge
pool may be formed. If erosion cannot be tolerated, a plunge pool is created by constructing an
auxiliary dam downstream of the main dam. Alternatively, a basin is excavated and it is provided
with a concrete apron.When tail water depth is sufficient, a hydraulic jump would form when the
water jet falls upon a flat apron. Free over-fall spillways are restricted only to situations where the
hydraulic drop from reservoir level to tail water level is less than about six metres.
7. TUNNEL SPILLWAY: Tunnel spillway discharges water through closed channels or tunnels
laid around or under a dam. The closed channels can be in the form of a vertical or inclined shaft, a
conduit constructed in an open cut and backfilled with earth materials, or a horizontal tunnel through
earth or rock. In narrow canyons with steep abutments as well as in wide valleys with abutments far
away from the stream channel, tunnel spillways may prove to be advantageous. In such situations,
conduit of the spillway can be easily located under the dam near the stream bed.

OGEE SPILLWAY:
FREE OVER-FALL SPILLWAY
CHUTE (TROUGH) SPILLWAY
SHAFT (MORNING GLORY OR GLORY HOLE) SPILLWAY

SIDE CHANNEL SPILLWAY
SIPHON SPILLWAY
DESIGN OF OGEE SPILLWAY:
Several standard ogee shapes have been developed by U.S. Army Corp and Waterways
Experimeniaf.Station (WES). Such shapes are known as 'WES .Standard Spillway Shapes':
Discharge Formula for the Ogee Spillway. The discharge passing over the ogee spillway is given by the
equation :

Thus, for a spillway having a vertical u/s face, the downstream crest (D/S profile) is given by the equation
According to the latest studies of U.S. Army Corps, the u/s curve (D/s profile) of the ogee spillway having a
vertical u/s face, should have the following equation:

ENERGY DISSIPATION DEVICES:
Different types of energy dissipators may be used along with a spillway, alone or in combination of
more than one, depending upon the energy to be dissipated and erosion control required downstream
of a dam. Broadly, the energy dissipators are classified under two categories – Stilling basins or
Bucket Type. Each of these are further subcategorized as given below.
STILLING BASIN TYPE ENERGY DISSIPATORS
a) Hydraulic jump type stilling basins
1. Horizontal apron type

2. Sloping apron type
b) Jet diffusion type stilling basins
1. Jet diffusion stilling basins

2. Interacting jet dissipators
3. Free jet stilling basins
4. Hump stilling basins
5. Impact stilling basins
BUCKET TYPE ENERGY DISSIPATORS
1. Solid roller bucket

2. Slotted roller bucket
3. Ski jump (Flip/Trajectory) bucket

MODULE 3 : DIVERSION HEAD WORKS
A diversion head-works is a structure constructed across a river for the purpose of raising water
level in the river so that it can be diverted into the off taking canals. It is also known as canal head
works.
Objectives of Diversion Head Works:
To rise the water level at the head of the canal.

To form a storage by constructing dykes (embankments) on both the banks of the river so that water
is available throughout the year
To control the entry of silt into the canal and to control the deposition of silt at the head of the canal
To control the fluctuation of water level in the river during different seasons
TYPICAL LAYOUT OF DIVERSION HEAD WORKS

DESIGN OF APRONS:
Bligh’s Creep Theory (1912)

Khosla’s Theory (1936)
Bligh’s Creep Theory (1912)
Assumptions:
1. Hydraulic Gradient is constant throughout the impervious length of the apron.
2. Creep Length is the sum of horizontal and vertical creep.
3. Stoppage of percolation by cut off or sheet pile possible only if it extends up to impermeable soil
strata.

LIMITATIONS:
1. No distinction between horizontal and vertical creep.
2. Holds good so long as horizontal distance between the pile lines is greater than the twice their depth
3. Did not explain about Exit Gradient
4. No distinction between outer and inner faces of sheet piles or the intermediate sheet piles, whereas
from investigation it is clear that the outer faces of the end sheet piles are much more effective than
inner ones.
5. Losses of head does not take place in the same proportions as the creep length. Also the uplift
pressure distribution is not linear but follow a sine curve
6. Bligh does not specify the absolute necessity of providing a sheet pile at downstream which is
essential to prevent undermining or piping.
SIMPLE PROBLEMS ON BLIGH’S THEORY:

KHOSLA’S THEORY (1936)
After studying a dam failure constructed based on Bligh’s theory, Khosla came out with the following;
1. Outer faces of end sheet piles were much more effective than the inner ones and the horizontal
length of the floor.
2. Intermediated piles of smaller length were ineffective except for local redistribution of pressure.
3. Undermining of floor started from tail end.
4. It was absolutely essential to have a reasonably deep vertical cut off at the downstream end to
prevent undermining.

Most designs do not confirm to elementary profiles (specific cases). In actual cases, we may have a
number of piles at upstream level, downstream level and intermediate points and the floor also has
some thickness.
Method of independent variable: This method consists of breaking up a complex profile into a number
of simple profiles. The pressures obtained at the key points by considering simple profile are then
corrected for the following:
1. correction for the thickness of floor
2. correction for mutual interference of piles
3. correction for slope of the floor.

MODULE 4:
CROSS DRAINAGE WORKS:
WHAT IS CROSS DRAINAGE WORK
when the network of main canals, branch canals, distributaries, etc.. are provided, then these canals
may have to cross the natural drainages like rivers, streams, nallahs, etc. at different points.
The crossing of the canals with such obstacle cannot be avoided.
So, suitable structures is constructed at the crossing point for the easy flow of water of the canal and
drainage in the respective directions.
These structures are known as cross-drainage works
Irrigational Canals while carrying water have to cross few natural drainage streams, rivers, etc..
To cross those drainages safely by the canals, some suitable structures are required to construct.
Works required to construct, to cross the drainage are called Cross Drainage Works (CDWs).
At the meeting point of canals and drainages, bed levels may not be same.
Depending on their bed levels, different structures are constructed and accordingly they are known
by different names.
Necessity of Cross Drainage Works.
The water-shed canals do not cross natural drainages. But in actual orientation of the canal network,
this ideal condition may not be available and the obstacles like natural drainages may be present
across the canal. So, the cross drainage works must be provided for running the irrigationsystem.
At the crossing point, the water of the canal and the drainage get intermixed. So, far the smooth
running of the canal with its design discharge the cross drainageworks are required.
The site condition of the crossing point may be such that without any suitable structure, the water of
the canal and drainage can not be diverted to their natural directions. So, the cross drainage works
must be provided to maintain their natural direction of flow.
TYEPS OF CDWS
(1) Type I (Irrigation canal passes over the drainage)
(a) Aqueduct, (b) Siphon aqueduct.
(2) Type II (Drainage passes over the irrigation canal)
(a) Super passage, (b) Siphon super passage.
(3) Type III (Drainage and canal intersection each other of the same level)
(a) Level Crossing, (b) Inlet and outlet.

Cross drainage works carrying canal across the drainage:

the structures that fall under this type are:
1. An Aqueduct
2. Siphon Aqueduct
Aqueduct:
When the HFL of the drain is sufficiently below the bottom of the canal such that the drainage waterflows
freely under gravity, the structure is known as Aqueduct.
 In this, canal water is carried across the drainage in a trough supported on piers.
 Bridge carrying water
 Provided when sufficient level difference is available between the canal and natural and canal bed is
sufficiently higher than HFL.
Siphon Aqueduct:
In case of the siphon Aqueduct, the HFL of the drain is much higher above the canal bed, and water runs under
siphon action through the Aqueduct barrels. The drain bed is generally depressed and provided with pucci
floors, on the upstream side, the drainage bed may be joined to the pucca floor either by a vertical drop or by
glacis of 3:1. The downstream rising slope should not be steeper than 5:1. When the canal is passed over the
drain, the canal remains open for inspection throughout and the damage caused by flood is rare. However
during heavy floods, the foundations are susceptible to scour or the waterway of drain may get choked due to
debris, tress etc.

2 Cross drainage works carrying drainage over canal.

The structures that fall under this type are:
Super passage
Canal siphon
Super passage:
 The hydraulic structure in which the drainage is passing over the irrigation canal is known assuper passage.
This structure is suitable when the bed level of drainage is above the flood surface level of the canal. The water
of the canal passes clearly below the drainage
 A super passage is similar to an aqueduct, except in this case the drain is over the canal.
 The FSL of the canal is lower than the underside of the trough carrying drainage water. Thus, the canal water
runs under the gravity.
 Reverse of an aqueduct
Canal Syphon:
• The hydraulic structure in which the drainage is taken over the irrigation canal, but the canal water
passes below the drainage under symphonic action is known as siphon super passage.
• This structure is suitable when the bed level of drainage is below the full supply level of the canal.

TYPE III DRAINAGE AND CANAL INTERSECT EACH OTHER AT THE SAME LEVEL.
• Level Crossings •
When the bed level of canal and the stream are approximately the same and quality of water in canal
and stream is not much different, the cross-drainage work constructed is called level crossing where
water of canal and stream is allowed to mix. With the help of regulators both in canal and stream,
water is disposed through canal and stream in required quantity. Level crossing consists of following
components (i) crest wall(ii)Stream regulator(iii)Canal regulator.
INLET AND OUTLET
• When irrigation canal meets a small stream or drain at same level, drain is allowed to enter the canal
as in inlet. At some distance from this inlet point, apart of water is allowed to drain as outlet which
eventually meets the original stream. Stone pitching is required at the inlet and outlet. The bed and
banks between inlet and outlet are also protected by stone pitching. This type of CDW is called Inlet
and Outlet.
HYDRAULIC DESIGN OF AQUIDUCT (Channel Transitions)
The following methods may be used for designing the channel transitions:
• Mitra’s method of design of transition (when water depth remains constant)
• Chaturvedi’s method of design of transitions (when the depth remains constant)
• Hind’s method of design of transitions (when water depth may or may not vary).

MITRAS METHOD OF DESIGN TRANSITION WHEN WATER DEPTH

REMAINSCONSTANT:
• Shri A.C. Mitra, Chief Engineer, U.P, Irrigation Department has proposed a hyperbolic transition for
the design of channel transitions. According to him, the channel width at any section X-X, at a
distance x from the flumed section is given by.


SOLUTION:
(Design of Transitions only)


MODULE 5 : CANAL REGULATION WORKS

The common structures used in the Canal regulation works are
1. Drops and falls, to lower the water level of the canal

2. Cross regulators, to head up water in the parent channel to divert some of it through an off take
channel, like a distributary.
3. Distributary head regulator, to control the amount of water flowing in to off take channel.
4. Escapes, to allow release of excess water from the canal system.
INTRODUCTION:
It consists of a raised crest with abutments on both sides. The crest may be subdivided in various bays
by providing piers on the crest. The piers support roadway and a platform for operating gates. The
gates control the flow over the crest. They are housed and operated in grooves made in the abutments
and piers. Sill of the regulator crest is raised to prevent silt entry. Sometimes the gates are provided in
tiers. Then lower tiers may be kept closed to raise the sill of the regulator.
The head regulator is generally constructed with masonry. It should be founded on a good rock
foundation. It should be safe against shear, sliding and overturning. It should be flanked with adequate
wing walls. The head regulator should also be given proper protection by providing aprons on
upstream and downstream side of the barrel. To prevent seepage cutoff is also essential. To take
irrigation water at low velocities waterway of the head regulator should be sufficiently big.
FUNCTIONS OF REGULATOR:
i. It regulates the flow of irrigation water entering into the canal.
ii. It can be used as a meter for measuring the discharge.
iii. It regulates and prevents excessive silt entry into the canal.
FUNCTIONS OF CROSS REGULATOR:
(i)When due to inadequate supply the water level is lowered the off-taking channels do not get their
proper share. A cross regulator is provided to raise the water level.
(ii) Sometimes it becomes necessary to carry out some necessary to carry out some repair works on a
canal. The cross regulator if existing above that reach of the canal, it can be closed and repairs can be
done efficiently.
(iii) Sometimes it is necessary to close the canal below a particular point. Say when there is no
demand for irrigation water during a particular period.
(iv) When the costly headwork’s are not constructed in the initial stages, the cross-regulator helps in
regulating the canal supplies.

(v) Cross regulators divide long canal reach into smaller ones and make it possible to maintain the
reach successfully and efficiently. For efficient functioning they should be spaced 10 to 13 km apart
on the main canal and 7 to 10 km on the branches.
FUNCTIONS OF DISTRIBUTARY HEAD REGULATOR:
It is a hydraulic structure constructed at the head of a distributary. This regulator performs

the same functions as that of a head regulator.
i. It regulates the supply of the distributary.
ii. It can be used many times as a meter.
iii. It is also a silt selective structure.
iv. Distributary head regulator controls the flow in the distributary. By closing the gates
distributary can be dried to carry out repairs or maintenance works.
CANAL FALLS:
Irrigation canals are designed for a prescribed bed slope so that velocity becomes non silting or non
scouring. But if the ground topography is such that in order to maintain the canal designed slope,
indefinite filling from falling ground level is to be made. This indefinite filling is avoided by
constructing a hydraulic structure in the place of sudden bed level. This hydraulic structure is called
canal fall or drop. Beyond the canal fall, canal again maintains its designed slope.
Whenever the available natural ground slope is steep than the designed bed slope of the channel, the
difference is adjusted by constructing vertical ‘falls’or‘drops’in the canal bed at suitable intervals, as
shown in figure below. Such a drop in a natural canal bed will not be stable and, therefore, in order to
retain this drop, a masonry structure is constructed. Such a structure is called a Canal Fall or a Canal
drop.
Thus, a canal fall or drop is an irrigation structure constructed across a canal to lower down its bed
level to maintain the designed slope when there is a change of ground level to maintain the designed
slope when there is change of ground level. This falling water at the fall has some surplus energy.The
fall is constructed in such a way that it can destroy this surplus energy.
Necessity of Canal Falls :
1) When the slope of the ground suddenly changes to steeper slope, the permissible bed slope can
not be maintained. It requires excessive earthwork in filling to maintain the slope. In such a
case falls are provided to avoid excessive earth work in filling

2) When the slope of the ground is more or less uniform and the slope is greater than the
permissible bed slope of canal.
3) In cross-drainage works, when the difference between bed level of canal and that of drainage is
small or when the F.S.L of the canal is above the bed level of drainage then the canal fall is
necessary to carry the canal water below the stream or drainage.
TYPES OF CANAL FALL
Depending on the ground level conditions and shape of the fall the various types of fall
are :
Ogee Fall
The ogee fall was constructed by Sir Proby Cautley on the Ganga Canal. This type of
fall has gradual convex and concave surfaces i.e.in the ogee form. The gradual convex
and concave surface is provided with an aim to provide smooth transition and to reduce
disturbance and impact. A hydraulic jump is formed which dissipates a part of kinetic
energy. Upstream and downstream of the fall is provided by Stone Pitching.
Stepped Fall
It consists of a series of vertical drops in the form of steps. This steps is suitable in
places where sloping ground is very long and require a long glacis to connect the higher
bed level u/s with lower bed level d/s. it is practically a modification of rapid fall. The
sloping glacis is divided into a number drops to bring down the canal bed step by step
to protect the canal bed and sides from damage by erosion. Brick walls are provided at
each drop. The bed of the canal within the fall is protected by rubble masonry with
surface finishing by rich cement mortar.

Vertical Fall ( Sarda Fall)

In the simple type, canal u/s bed is on the level of upstream curtain wall, canal u/s bed
level is below the crest of curtain wall. In both the cases, a cistern is formed to act as
water cushion. Floor is made of concrete u/s and d/s side stone pitching with cement
grouting is provided. This type of fall is used in Sarda Canal UP and therefore, it is
also called Sarda Fall.
Rapid Fall
When the natural ground level is even and rapid, this rapid fall is suitable. It consists of
long sloping glacis. Curtain walls are provided on both u/s and d/s sides. Rubble
masonry with cement grouting is provided from u/s curtain wall to d/s curtain wall.
Masonry surface is finished with a rich cement mortar.
Straight Glacis Fall

It consists of a straight glacis provided with a crest wall. For dissipation of energy of
flowing water, a water cushion is provided. Curtain walls are provided at toe and heel.
Stone pitching is required at upstream and downstream of the fall.

Trapezoidal Notch Fall

It was designed by Reid in 1894. In this type a body or foundation wall across the
channel consisting of several trapezoidal notches between side pier and intermediate
pier is constructed. The sill of the notches are kept at upstream bed level of the canal.
The body wall is made of concrete. An impervious floor is provided to resist the
scouring effect of falling water. Upstream and downstream side of the fall is protected
by stone pitching finished with cement grouting
Montague Type Fall

• In the straight glacis type profile, energy dissipation is not complete. Therefore,
montague developed this type of profile where energy dissipation takes place.
Inglis or Baffle Fall

• Here glacis is straight and sloping, but baffle wall provided on the downstream floor
dissipate the energy. Main body of glacis is made of concrete. Curtain walls both at toe
and heel are provided. Stone pitching are essential both at u/s and d/s ends

CANAL OUTLETS :
These modules are classified in three types, which are as follows:

(a) Non-modular outlets
These outlets operate in such a way that the flow passing through them is a function of
the difference in water levels of the distributing channel and the watercourse. Hence, a
variation in either affects the discharge. These outlets consist of regulator or circular
openings and pavement. The effect of downstream water level is more with short
pavement.
(b) Semi-modular outlets
The discharge through these outlets depend on the water level of the distributing
channel but is independent of the water level in the watercourse so long as the
minimum working head required for their working is available.
(c) Module outlets
The discharge through modular outlets is independent of the water levels in the
distributing channel and the watercourse, within reasonable working limits. This type of
outlets may or may not be equipped with moving parts.Though modular outlets, like the
Gibb’s module, have been designed and implemented earlier, they are not very
common in the present Indian irrigation engineering scenario.

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Dr.H.S.Govardhana Swamy , Head of Civil Engineering Department .

MODULE 1: GRAVITY DAMS

Dams can be classified according to different criteria, as given below:

(a) Based on Function Served:

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drift wood flowing in the river with water.

(e) Based on the structural action:

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Forces Acting on Gravity Dam

A gravity dam is subjected to the following main forces:

1. Weight of the dam

2. Reservoir and Tail water loads (Water pressure)

It acts horizontally at a height of h/3 above the base of the dam.

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RajaRajeswari College of Engineering / 9663736535

RajaRajeswari College of Engineering / 9663736535

Elementary Profile of a Gravity Dam

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Base width of the elementary profile

Practical Profile of a Gravity Dam

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Safety against Overturning

Safety against Sliding

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MODULE 2 : EARTH DAMS

Classification of Earth Dams:

Earth dams are classified as follows:

1) Based on method of construction :

Hydraulic fill earth dam: In type of dam, excavation, transportation and

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Homogeneous earth dam: Constructed with uniform and homogeneous

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Hydraulic failures: Following are the various types of hydraulic failures:

1) Overtopping :when the free board and capacity of the spillway is

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Following are the various types of seepage failures:

1) Piping through body of the dam:

2) Piping through foundation of the dam:

When highly pervious material is used in the construction foundation of the

Following are the various types of seepage failures:

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Types of failures—Earth dams

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Design Criteria of Earth Dams

The conditions to be satisfied are as follows.

(a) Spillway capacity should be sufficient to pass the flood flow.

The conditions to be satisfied are as follows

SEEPAGE CONTROL IN EARTHEN DAMS:

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Control of Seepage through Foundations

1. by providing drainage trenches.

Control of Seepage through Embankments

1. by providing horizontal drainage filters.

SECTION OF AN EARTH DAM:

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 Straight Drop Spillways

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FREE OVER-FALL SPILLWAY