Hydraulic structure-I.pptx

Ambo University,
Hachalu Hundessa Campus
Department of Hydraulic & Water Resources Engineering
Hydraulic Structures I [CEng 3171]
Civil 4th year (Cep program)
Semester I,
By Dereje G. (MSc. Water supply and Sanitary
Engineering)
April, 2023

..Cont..
Course code: CEng 3171
Course Title: Hydraulic
Structures I
Module Title: Design of
Hydraulic Structures &
Irrigation
Course Objectives
 The main objectives of
this course is to equip
students with knowledge
on analysis and design
hydraulic structures
1. Dams in general
1.1 General (Hydraulic
Structures)
1.2 Selection of type of
dam and their
classification
1.3 Selection of dam site
2. Gravity dams
2.1 Definition
2.2 Typical classification /
Types of Concrete Gravity
Dams
2.3 Forces affecting on
gravity dam / Loads on
gravity dams

..cont..
2.4 Modes of failure and
criteria for structural
stability of gravity dams
2.5 Two-dimensional
stability analysis / Stability
Analysis
2.6 Design consideration
and fixing the section of a
dam
2.7 Design example of
gravity dam
2.8 Construction aspects of
gravity dams (diversion,
cracking, joints, and
foundation treatment)
3. Arch and Buttress
dams
3.1 Definition and type of
arch dams
3.2 Forces acting on arch
dams / Loads on
3.3 Design considerations
3.4 Design of arch dams
3.5 Definition of types of
buttress dams
3.6 Forces acting on
buttress dams / Loads on
3.7 Design of buttress
dams

..cont..
4. Earthen and Rock fill
dams / Embankment Dams
4.1 Introduction / Definition
4.2 Types of embankment
dams
4.3 Methods of construction
4.4 Causes of failures of
earthen dams
4.5 Design criteria for earth
dams
4.6 Selecting a suitable
preliminary section of an earth
dam
4.7 Seepage discharge through
Iso/non isotropic soils /
Seepage analysis.
4.8 Stability analysis
4.9 Seepage control
4.10 Design example of
earth dam
4.11 Rock fill dam
5. Spillways, energy
dissipaters and spillway
gates
5.1 Introduction
5.2 Location of a spillway
5.3 Design considerations
for the main spillway
5.4 Types of spillways
5.5 Energy dissipation
below spillways

..cont..
5.6 Stilling basins
5.7 Spillway gates
5.8 Design example of a
spillway
5.9 Outlet works through
dams and river intakes
5.10 Sluice ways or dam
outlets
5.11 Hydraulics of outlet
works
5.12 Trash racks
References:
 Irrigation Engineering and
Hydraulic Structures, Santosh
Kumar Garg, Latest Edition,
 Irrigation and Water Power
Engineering, Pande B. B. Lal
2005,
 Hydraulic Structures, P Novak
Latest Edition, Design of small
Dams, USBR publications,
 Geotechnical Aspects of
Embankment Dams, Published
in Australia
 Reading List: Dam
Engineering (Vol I., II., III)
Grigger

Hydraulic structure-I
What is hydraulic structure?
A structure submerged or partially submerged in
any body of water, which disrupts(disturbs) the
natural flow of water.
They can be used to divert, disrupt or completely
stop the flow.
An example of a hydraulic structure would be a
dam, weir, and Barrage etc.
Are used to control and manage the flow of water
in natural and built systems.

1. Dams in general
What is a dam?
A dam is defined as a barrier(obstruction) or
structure across a stream, river or waterway to
confine and then control the flow of water.
Dams vary in size from small earth
embankments, often for farm use, to high
massive concrete structures generally used for
water supply, hydropower and irrigation.
A barrier constructed to hold back water and raise
its level, forming a reservoir used to generate
electricity or as a water supply

..Cont..
Reservoirs created by dams not only suppress
floods but also provide water for activities such as
irrigation, human consumption, industrial use,
aquaculture, and navigability.
Hydropower is often used in combination with
dams to generate electricity.
A dam can also be used to collect or store water
which can be evenly distributed between locations

History of the Dam in the world and Ethiopia
A dam is a human-made structure that is
primarily used to hold back water.
Dams are constructed for many purposes,
including reservoir creation, flood prevention,
irrigation, and hydroelectric power.
Today, there are almost 50,000 large dams in use
worldwide
The first known dam to be built is the Jawa Dam
since 300 BC.

Dam history in Ethiopia
Aba Samuel Dam
The Akaki–Aba-Samuel wetlands are part of the
Awash river catchment,20 km south-east of Addis
Ababa
The reservoir was created in 1939 to produce
electricity for Addis Ababa.
Production continued until 1970 when the
machinery became too old to maintain and the
plant stopped working.
The first large hydropower plant in Ethiopia, the
Tekeze dam, was out of production because of
drought.

..cont..
Question!
Does it mean that, a Dam has stopped working
means its structure is collapsing or what, what do
you think ?
Let you give your feedback!

..cont..
Embankment dams are the most common type of
dam in use today.why?
Materials used for embankment dams include
natural soil or rock, or waste materials obtained
from mining or milling operations.
Masonry or concrete dams may be categorized
according to the designs used to resist the stress
due to reservoir water pressure.

..cont..
The Grand Ethiopian Renaissance Dam(GERD)
 Designed to trap 100 years of sediment
inflow.
 GERD is a 6,450 MW hydropower project
nearing completion on the Blue Nile in
Ethiopia,
Located about 30 km upstream of the
border with Sudan.
What are the benefits of constructing
GERD closer to the Sudan Dam?
It will be the largest hydropower project in
Africa.

..Cont..
It has 175m height
It’s width varies around spillway above
600m
The length of GERD is around 2km.

..cont..
Question:2
List the number of dams in our country, the
power they generate, where they are located, and
what types they are?

1.2 Selection of type of dam and their
classification
Dams can be classified as per
Their functions,
material of construction,
and structural design:
(i) Classification based on function:
(a) Storage (or impounding) dam
is constructed across a river to create a reservoir for
storing water during the period when the flow river
is in excess.
This stored water is then used for irrigation, power
generation and water supply when the demand
exceeds the flow in the river.

..cont..
(b) Detention dam
 is primarily constructed to detain all or part of the
flood waters of a river
Released later in such a way that the region
downstream of the dam is safe against flood
damages.
A dam can also serve both the functions of
detention as well as storage.
(c) Diversion dam
is constructed for the purpose of diverting
water into a canal.
Such a dam is usually called diversion weir.

..cont..
(d) Coffer dam
is a temporary dam constructed to keep water
away from a specific area to keep it dry for some
specific purpose, such as construction of the main
dam. How?
The coffer dam too acts like diversion dam.
(e) Debris dam
is constructed across a river to trap sediments of
the river( also called sluice way).

..cont..
(ii) Based on material of construction;
(a) Earth and rock fill dams
 are constructed of loose earth (ranging from fine material
to big rock pieces) without any binding material.
 An earth dam having its major portion built of rocks is
called rock fill dam.
 Such dams are also known as non-rigid dams.
(b) Masonry dams
 are rigid dams constructed of either stone or brick
masonry.
(c) Concrete dams
 Are too rigid dams constructed of concrete.

..cont..
(iii) Based on structural design:
(a) Earth and rock fill dams
are non-rigid dams constructed of loose earth
material.
Shear strength of the soil used in the construction of
these dams opposes the forces exerted on the dam by
water.
The difference between an earth and rock fill dam is
that in case of rock fill dam major portion of the dam
is primarily made of rock pieces,
Whereas in case of the earth dam it is the soil which
is used for the construction of embankment.
Rock fill dam will be possible in all weather
conditions than earth dam.why?,how?

..cont..
Advantages of embankment Dam
They can be constructed on any type of foundation.
They can be constructed in comparatively less time.
They do not require skilled labour.
Initial cost of construction is low as locally available
soils, and rock boulders are normally used.
Their height can be increased without any difficulty.
They are specially suitable for conditions where
slopes of river banks are very flat.
Gravity dams under such conditions are not found
suitable.

..cont..
Disadvantages of Embankment Dam
 They fail all of the sudden without giving any pre-
warning.
 Flood waters affect the dam safety.
 Spillway have to be located independent of the
dam.
 They cannot be constructed as overflow dams.
 They require continuous maintenance.
 They cannot be constructed in narrow steep
valleys.
 They cannot withstand heavy rains unless
properly protected.
 They cannot be constructed in large heights.
 The usual height is 30 m for which most of the
earthen dams are constructed.

..cont..
(b) Gravity dam
 Concrete dam which resists the forces exerted upon it due
to all applied loads, and its own weight.
 The downstream face of a gravity dam usually has a
uniform slope.
 intersect the vertical upstream face at or near the
maximum water level in the reservoir.

..cont..
Advantages of Gravity Dam
Maintenance cost is negligible.
They are specially suitable for deep steep valley
conditions where no other dam is possible.
If suitable foundation is available, such dams can
be constructed for very large heights.
Because they can be constructed in very large
heights, they can store more amount of water.

..cont..
If suitable separate place is not available for
installation of spillways, they can be installed in
the dam section itself.
This dam gives prior indication of instability.
If remedial measures are taken in time, unsafe
dams may even be rendered safe.
Silting rate of the reservoir can be reduced
considerably by installing under sluices in the dam
near the bed of the reservoir.

..cont..
Sluices can be operated from time to time and
silt may be scoured out of the reservoir.
They are not affected by very heavy rainfall.
Earth dams cannot sustain very heavy rainfall
because of heavy erosions.

..cont..
Disadvantages of Gravity Dam
They are very costly in initial construction.
They take lot of time of construct.
They require skilled labour for construction.
Such dams can be constructed only on good
foundation.
If height of the dam is to be raised, it cannot be
done unless provision for it had been made in the
construction of the lower part of the dam.
i.e. increasing the height of dam is difficult.

..cont..
(c) Arch dam
is a curved masonry or concrete dam having
its convex face upstream.
Such a dam resists forces, exerted upon it
due to water pressure, by arch action.

..cont..
Advantages Arch Dam
They are particularly suitable for narrow deep gorges.
 Arch dams prove even more suitable than gravity
dams.
They require comparatively very small amount of
construction material.
The section or thickness of the dam is very small in
comparison to the gravity dam.
Uplift pressure is not very large as base width of the
dam is quite small.
They can be constructed on moderate foundations.

..cont..
Disadvantages of Arch Dam
They require very complicated form work which
is very costly.
They require very skilled labour.
Design of the dam is also difficult.
Speed of construction is very slow.
They require very strong solid rocky abutments
to resist the thrust of the arch.why ?
i.e,

..cont..
Because of;
In arch Dam a diagonal force, called thrust,
that will cause the arch to collapse if it is not
properly buttressed.
Hence, the vertical supports, upon which an
arch rests must be massive enough to buttress
the thrust and conduct it into the foundation.

..cont..
(D) Buttress Dam
 has a sloping deck which retains water
 Is modification of concrete gravity Dam.
 Which contains hollow dam
 Concrete saved relative to gravity dam 30–60%.

..cont..
Advantages of Buttress Dam
They can be constructed on weak foundation
because they are less massive than gravity dams.
The load of water lying on the inclined deck slab
adds to the vertical component of the dam and as
such helps in increasing the stability of the dam.
The factor of safety in case of buttress dams is far
greater than for gravity dams.
Height of buttress dams can be increased by
extending both buttresses and deck slab

..cont..
Power houses or other plants can be located in
the empty space between buttresses.
They require only half to one-third amount of
cement concrete in relation to the concrete
required for gravity dam for the same height.

..cont..
Disadvantages
More skilled labour is required.
Shuttering cost is more.
The slab being very thin, its face in contact with
water is likely to deteriorate and cause damage to
the dam.
It is more dangerous for intentional abuse.
It requires constant maintenance and supervision.
The dam life is shorter than that of other dams,why
?

1.3 Selection of dam site
Site Selection Criteria for Dam
Suitable foundation must be available.
For economy, the length of the dam should be as
small as possible and
for given height it should store maximum amount
of water.
A suitable site for the spillway should be available
in or nearby vicinity.
The bed level at the dam site should preferably be
higher than that of the river basin.why?

..cont..
i.eThis will reduce the height of the dam and will
facilitate the drainage problem.
The reservoir basin should be reasonably water-
tight.
Material required for the construction of the dam
should be easily available locally.
The value of the land and property submerged by
the proposed dam should be as low as possible.

..cont..
The dam site should be easily accessible,
it can be economically connected to important
towns.
Site for establishing labour colonies and healthy
environment should be available near by vicinity.

..cont..
Selection of Type of Dam
1. Topography :
A narrow U-shaped valley flowing between high
rocky walls would suggest a concrete dam.
A wide shape plane country would suggest an
earth fill dam.
A narrow V-shaped valley indicates choice of an
arch dam.

..cont..
2. Geology and Foundation Conditions :
The foundation strata should be strong
enough to carry weight of dam.
Hence the dam site must be surveyed by
geologists so as to detect the thickness of
foundation strata, presence of faults,
fissured material etc.
The various types of foundations generally
encountered are :-
Solid-rock foundation :
Similar like granite, gnesis etc.

..cont..
Almost every type of dam can be built as it is
strong enough to withstand the self weight of
the dam and external forces acting on the dam.
Gravel foundation :
This type of foundation is suitable for earth
and rock fill dams.
For this foundation, low concrete gravity dams
up to height of 15 meter may also be
suggested

..cont..
Silt and fine sand foundation :
This type of foundation suggests the adoption of
earth or very low gravity dam, up to height of 8
meter.
Clay foundation :
This foundation may be accepted for earthen dam
after special treatment.
3. Availability of Materials :
the materials required for its construction must be
available locally at short distance from the
construction site

..cont..
4. Spillway size and location :
The cost of constructing a separate spillway may
be enormous or sometimes suitable site for
construction of spillway may not be available.
In such cases combining the spillway and dam
into one structure may be desirable.
5. Earthquake zone :
If dam is located in earthquake zone, its design
must include the earthquake forces.

..cont..
6. Height of Dam :
Earthen dams are usually not provided for height
more than 30 meter.
Hence for greater height, gravity dams are
generally preferred.
7. Other consideration :
It includes life of dam, the width of roadway to be
provided over the dam,
Overall cost of the construction and maintenance.

..cont..
In general;
If the river valley is narrow and the geological
conditions are good, then it is suitable for an arch
dam;
if the river valley is wide and the geological
conditions are relatively good, a gravity dam may
be selected
Wide valley with deep over burden:fine-grained
deposits, e.g. Fine glacial soils, tills etc., over 5m
deep favour earthfill embankment dam

..cont..
If the river valley is wide, the riverbed overburden is
deep and thick or the geological conditions are
relatively poor, and the local material reserves such
as earth, stone and gravel are abundant, it is suitable
for an earth and rock fill dam.
With regard to a gravity dam site, the rocks shall
have sufficient strength, integrity and homogeneity;
with regard to a concrete arch dam site, the
requirements for rock mass strength and integrity are
greater than those for a gravity dam, meanwhile the
dam abutment shall be stable.

..cont..
With regard to earth and rock fill dam sites, it is
necessary to ascertain(check) the thickness of
dam foundation overburden, and verify whether
liquefiable soil layer exists in the dam foundation.
Gravity Dam:-They are more durable and solid
than rock-fill and earth dam.
They can be constructed on site, where the natural
foundation is strong enough to bear the self-
weight of dam.
Arch Dam:It is preferred when the site is extremely
high and narrow valley portion is available.

Hydraulic structure-I.pptx

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