Water Power Engineering

Hydrology

Hydrology is the study of the distribution and movement of

water both on and below the Earth’s surface, as well as the
impact of human activity on water availability and conditions.

The scientific study of the properties, distribution, and effects of

water on the earth's surface, in the soil and underlying rocks,
and in the atmosphere
Hydrology is the science that encompasses the study of water
on the Earth’s surface and beneath the surface of the Earth, the
occurrence and movement of water, the physical and chemical
properties of water, and its relationship with the living and
material components of the environment.

Hydrologists typically do the following: Measure the properties

of bodies of water, such as volume and stream flow. Collect
water and soil samples to test for certain properties, such as
the pH or pollution levels. Analyze data on the environmental
impacts of pollution, erosion, drought, and other problems.

What is the importance of hydrology in water resource

development?
The basic role of hydrology, which is fundamental for water
resources management, is the accurate definition and
understanding of the water balance for different space and
time increments.
How important is hydrology in our daily lives?
The hydrologic cycle is important because it is how water
reaches plants, animals and us! Besides providing people,
animals and plants with water, it also moves things like
nutrients, pathogens and sediment in and out of aquatic
ecosystems.

What are the practical uses of hydrology?

Hydrology provides guidance for undergoing proper planning
and management of water resources. Calculates rainfall,
surface runoff, and precipitation. It determines the water
balance for a particular region. It mitigates and predicts flood,
landslide and drought risk in the region.

What does a hydrogeologist do every day?

On a daily basis, Hydrologists coordinate and supervise the
work of professional and technical staff, including research
assistants, technologists, and technicians. They study public
water supply issues, including flood and drought risks, water
quality, wastewater, and impacts on wetland habitats.

What does a hydrogeologist do?

A hydrogeologist is a person who studies the ways that
groundwater (hydro) moves through the soil and rock of the
earth (geology). A similar profession, a hydrologist, is someone
who studies surface water. Water is an essential part of life on
earth and is something that people, plants and animals need to
survive.

What is the difference between hydraulics and hydrology?

Hydrology – The study or science of transforming rainfall
amount into quantity of runoff. Hydraulics – The study or
science of the motion of liquids in relation to disciplines such
as fluid mechanics and fluid dynamics.

Hydropower pros and cons

Hydroelectricity, which is created by hydropower plants, is a
popular form of renewable energy that uses the flow of water
to generate electricity.

Hydropower, otherwise known as hydroelectric

power,Hydropower and pumped storage continue to play a
crucial role in our fight against climate change by providing
essential power, storage, and flexibility services

Pros and cons of hydroelectric energy

Hydropower pros and cons

Pros Cons
Renewable Environmental consequences
Low emissionsExpensive to build
Reliable Drought potential
Safe Limited reserves

Hydropower has been used for generations to provide the U.S.

with reliable, fossil fuel-free electricity.
It is a great renewable energy source because water is usually
very abundant, but it comes with some environmental
drawbacks. While the power source itself is carbon dioxide-free,
building dams along a river can have consequences for the
native fish species.
How hydroelectric energy works

Hydropower plants create energy by using the force of water to

turn turbines. They operate similarly to how a coal-powered
plant is run.
For example, when coal is burned in a coal plant, the steam
that is created powers turbines that then create electricity.
With hydropower, the energy source that generates power is
water.
The most popular form of hydropower, also known as
hydroelectric power, is a large dam that holds water in a
reservoir, like the picture below. When electricity is needed,
water is released from the reservoir, which then propels
turbines to produce electricity.

ADVANTAGES OF HYDROPOWER:

 Hydropower is a renewable source of energy. The energy

generated through hydropower relies on the water cycle,
which is driven by the sun, making it renewable.
 Hydropower is fueled by water, making it a clean source
of energy.
 Hydroelectric power is a domestic source of energy,
allowing each state to produce its own energy without
being reliant on international fuel sources.
 Impoundment hydropower creates reservoirs that offer
recreational opportunities such as fishing, swimming,
and boating. Most hydropower installations are required
to provide some public access to the reservoir to allow
the public to take advantage of these opportunities.
 Hydroelectric power is flexible. Some hydropower
facilities can quickly go from zero power to maximum
output. Because hydropower plants can generate power
 to the grid immediately, they provide essential backup
power during major electricity outages or disruptions.
 Hydropower provides benefits beyond electricity
generation by providing flood control, irrigation support,
and clean drinking water.
 Hydropower is affordable. Hydropower provides low-cost
electricity and durability over time compared to other
sources of energy. Construction costs can even be
mitigated by using preexisting structures such as bridges,
tunnels, and dams.
 Hydropower compliments other renewable energy
sources. Technologies like pumped storage
hydropower (PSH) store energy to use in tandem with
renewables such as wind and solar power when demand
is high.

Advantages of hydroelectric energy

1. Renewable

Hydroelectric energy is classified as a renewable energy source

because it is powered by water, and water is a naturally
replenishing resource.
Since water is the energy source that powers a hydropower
plant, there is no pollution emitted during the generation of
power. Both of these factors make hydropower renewable,
because water is naturally replenishing and because it is not a
source of greenhouse gas emissions.
2. Low emissions

The action of generating electricity with hydropower energy

does not emit carbon dioxide, a greenhouse gas that drives
global climate change.
After a hydropower plant is built, it does not emit pollution into
the atmosphere like many of its non-renewable energy
counterparts, like coal and natural gas.

3. Reliable

Hydroelectricity is a very reliable renewable energy source.

Water flow is usually very predictable and is taken into
consideration when determining where a hydropower plant is
built, either on an actively flowing river or built with a dam to
manage water flow.
Additionally, the output of electricity can be adjusted. If energy
demand is low, water can be averted from the turbines and less
energy will be produced. The opposite is true if more energy is
needed - more water can flow into the plant for electricity
production.

4. Safe

Generally, hydropower is a very safe form of power

generation.
No sickness-causing pollution is emitted during energy
generation and there is zero chance of oil spills or gas pipes
breaking, since the only fuel used to power a hydropower plant
is water.

Disadvantages of hydroelectric energy

1. Environmental consequences

Hydropower facilities can be tricky because when one is built

with a dam, such as the famous Hoover Dam in Nevada, a
previously dry land area will be flooded with water, in order to
be used as a reservoir. That means whatever habitat was in
that location will be ruined. Also, the natural flow of the river
will be affected.
A non-natural water flow leads to issues ranging from less
sediment reaching the end of the river, a natural way to build
up and maintain land, to affecting fish migration patterns. Also,
many rivers travel through multiple counties and if they are
dammed, upstream countries could take more water than is
fair and leave less water for countries downriver.
Before choosing locations for hydropower plants, the potential
environmental effects should be carefully considered to make
sure that the plant can be as environmentally-friendly as
possible.

2. Expensive to build

Building any type of power plant is expensive - hydroelectric

power plants can cost as much as $580 per kilowatt to be built,
and they usually range from 10MW to 30MWs (where one MW
is equal to 1,000 kilowatts).
This means that the upfront cost of building a hydropower
plant can be millions of dollars. Compared to the falling prices
of solar installations, for example, hydropower is a more
challenging renewable project to finance.

3. Drought potential
The ability to create electricity can be severely reduced if there
is a drought and not enough water is flowing into the plant.
The good news is, most droughts are a short-lived break from
the typical water cycle and should only create a minor delay in
electricity generation.

4. Limited reservoirs

It is challenging to find a suitable spot that has a large

year-round water supply, with the right amount of water and is
close enough to existing power lines. It is also a delicate
balancing act to keeping enough river water wild (meaning
without dams), versus damming up many rivers for power.

Pros and Cons of Hydroelectric Energy

Pros of Hydroelectric Energy

There are many advantages of hydroelectric energy including

renewability, zero emissions, and even recreational
opportunities. Advantages of hydroelectric energy :

1. It’s Good for the Environment

Although hydroelectric energy does have some disadvantages,
it is one of the most environmentally friendly forms of energy
production available to us today. It does not use any fossil fuels,
nor does it produce any harmful emissions, and it also provides
a steady supply of clean energy. So, what’s not to love? While
dams can have a heavy impact on the environment, the only
pollution these dams create is from the initial construction. The
actual production of energy produces no carbon emissions.

2. It’s a Renewable Resource

“Water, water everywhere but not a drop to drink.” While you
won’t be drinking directly from a river (or ocean) anytime soon,
one of the main advantages of hydro energy is that water is
nearly everywhere and can be used to produce hydroelectric
energy. Because of the water cycle, it is a renewable resource
that doesn’t run out—allowing us to conserve limited and
non-renewable resources for other uses.

Hydroelectric energy is also a great resource because it creates

greater energy independence for countries. A reduced demand
for external fuel sources may help lessen conflict and improve
economic issues for countries that struggle to get fuel from
international sources. Instead, they can provide clean, domestic
power with hydro energy.

3. It’s Reliable and Highly Efficient

One of the biggest pros of hydroelectric energy is that it is one
of the most efficient energy resources in the world. Consider
that solar power is only a maximum of 30-36% efficient, wind
power only 25-45% efficient, and coal power is only 33-40%
efficient. All of these methods pale in comparison to hydro
energy, which is up to 90% efficient at converting water into
electricity.

Hydroelectric energy also has the advantage of little to no

downtime because the flow of water is only stopped for
general repairs, maintenance, and upgrades. Solar power, on
the other hand, decreases in production every night when the
sun goes down, and wind power is only good as long as there is
a steady breeze.

4. It’s Flexible
Unlike other forms of power like solar, wind, or coal,
hydroelectric energy is constant. The flow of water to produce
energy can easily be altered to meet supply demands. This
means that electricity can be made available when it’s needed,
which reduces energy waste.
5. It’s Safe
Compared to many other forms of energy production, dams
that produce hydro energy have been fairly safe over the years.
Most issues or problems that have occurred are the result of
poor construction and low safety standards in older dams.
Another advantage of hydroelectric energy in this situation is
that there is no combustible fuel involved, lowering the risks
associated with fossil fuels or nuclear energy.

6. It’s Economical
Although the initial expense can be hefty, once a hydroelectric
dam is up and running, the cost of maintenance and employee
wages is relatively low. Plus, water doesn’t fluctuate in cost the
way that traditional fossil fuels and imported fuels do.
Countries that use hydroelectric power can save a lot of money,
and some countries, like Paraguay, are able to get nearly all of
their energy from hydroelectric dams.

7. It’s Great for Recreational Use

Finally, dams typically create reservoirs. If you live near a
reservoir or have ever visited one, you know that it’s essentially
a man-made lake where people enjoy fishing, boating,
swimming, windsurfing, and more. There are even some
famous reservoirs you may have heard of like Lake Mead,
created by the Hoover Dam.

There are many great advantages of hydroelectric energy

including energy independence and a sustainable source of
energy for the future.

8. It’s a Fundamental Vehicle for Development

In addition to being an abundant source of energy, one of the
pros of hydroelectric energy is that it serves as an efficient and
fundamental vehicle for the development of both new and
established communities.
Hydroelectric power plants can do this in a number of ways, the
first being that they can supply a large amount of energy to
communities, even to those that are remote. They can also
supply cause for highway construction, attract various
industries, and give an overall boost in commerce. All of these
benefits serve to improve the overall quality of life of residents
who utilize this source of power.

In addition, hydroelectric energy creates sustainable

development, meaning that it won’t affect the capability of
future generations when it comes to tackling their own unique
needs in the future.

OR

1. Renewable

Hydropower is completely renewable, which means it will

never run out unless the water stops flowing. As a
result, hydro plants are built to last. In some cases, equipment
that was built to last 25 years is still operational after double
the amount of time has passed.

2. Emission Free

The creation of hydroelectricity does not release emissions into

the atmosphere. This is, of course, the biggest appeal of any
renewable energy source.

3. Reliable

Hydropower is, by far, the most reliable renewable energy

available in the world. Unlike when the sun goes down or when
the wind dies down, water usually has a constant and steady
flow 24/7.
4. Adjustable

Since hydropower is so reliable, hydro plants can actually adjust

the flow of water. This allows the plant to produce more energy
when it is required or reduce the energy output when it is not
needed. This is something that no other renewable energy
source can do.

5. Create Lakes

Lakes can be used for recreational purposes and can even help
draw in tourists. Look no further than Lake Mead. It was
created as a result of the Hoover dam and brought in over 7.5
million visitors in 2018. This can give nearby towns a huge
boost economically.

6. Faster Developed Land

Since hydro dams can only be built in specific locations, they

can help develop the land for nearby towns and cities. This is
because it takes a lot of equipment to build a dam. To transport
it, highways and roads must be built, which helps open new
paths for rural towns.

Cons of Hydroelectric Energy

The flip side to all these advantages of hydroelectric energy are

the disadvantages of hydroelectric energy. Here are a few of
the main disadvantages of hydroelectric energy :

1. It Has an Environmental Impact

Perhaps the largest disadvantage of hydroelectric energy is the
impact it can have on the environment. Dams can damage or
otherwise impact the environment both upstream and
downstream through their construction process during the
formation of the dam. To build a dam, new roads and power
lines must be installed that disrupt the environment. Dams also
often form reservoirs that flood large areas and displace
natural habitats. When dams flood areas, it creates sections of
still or stagnant water that kills vegetation which emits
greenhouse gasses as it rots. This is especially true in humid
and tropical environments.

Blocking the flow of water can also seriously impact fish

migration, especially for species like salmon that rely on rivers
to spawn. Dams can even impact biological triggers that tell fish
where to go when it’s time to migrate. Some dams have sought
to solve this disadvantage of hydroelectric energy by creating
fish ladders or fish elevators to help migratory fish make it to
their spawning grounds.

The final environmental disadvantage of hydroelectric energy

on our list is water quality. When dams are created, they limit
the flow of water, which affects the oxygen levels in the water.
Lower oxygen levels behind the dam can result in lower oxygen
levels downstream as well. When there is not as much oxygen
in the water, it is more difficult for some species of fish to
survive, which affects river habitats.

The increase in carbon dioxide and methane emissions from a

hydroelectric plant can also harm all forms of aquatic plant life.
The increased pollution of these greenhouse gases can cause
plant life beneath the water to rot, which can severely impact
the surrounding ecosystem.

2. It Displaces People
Reservoirs not only displace animals from their habitats, but
they also displace people. This disadvantage of hydroelectric
energy can have quite a large impact on communities. People
who have lived in an area their whole lives may be forced to
move, and although they are typically compensated for moving,
it can’t make up for what they have lost.

Cities, towns, and villages have been eliminated by dams, and

local cultures displaced. If people refuse to move due to
construction, they have sometimes been forced out of their
homes with the threat of violence.

In 1982, one instance in Guatemala resulted in the deaths of

369 Mayans who refused to move from their homes for the
construction of the Chixoy Dam. Over the years, dams have
displaced millions of people, forcing them to relocate their lives
and families elsewhere.

The construction of a hydroelectric plant also increases the risk

of flooding in lower elevations. Should strong water currents be
released from the dam, those living in lower elevations can
have their lives significantly altered, perhaps permanently.

3. It’s Expensive
Another disadvantage of hydroelectric energy is the expense
required to build a dam in the first place. Although they don’t
cost much to operate, the time it takes for a dam to pay for
itself can vary widely. Some dams take two to five years to
construct, while others like the Itaipu Dam in Brazil and
Paraguay can take significantly longer, leading to increased
costs. Everything totaled, the Itaipu Dam took 18 years and $18
billion to build.

Since the 1950’s, an estimated $2,000 billion has been spent on

dam construction around the world, with average construction
delays of 44% and overestimates on cost reaching an average
of 96%. Overspending and delays make it more difficult to get a
return on the money invested in the construction of the dam.
4. There are Limited Reservoirs
Although water is an unlimited resource, the conditions
necessary to build a dam are limited. This is a disadvantage of
hydroelectric energy because it means you cannot simply build
a dam anywhere you please. In fact, most locations that are
suitable for building hydroelectric dams have already been
used for this purpose. Another factor to consider is that even if
a location could support a hydroelectric dam, it may not
generate enough profit to make the project worthwhile.

5. There are Droughts

When weighing the advantages and disadvantages of
hydroelectric energy, it’s important to take into consideration
the fact that water can and does go through cycles of
abundance and drought. Lower than normal water levels can
heavily impact energy production and is a disadvantage of
hydroelectric energy.

Aside from being affected by drought, hydro energy production

can cause drought conditions downstream if they don’t allow
sufficient water to pass through. This can be especially
detrimental if a dam is located along a river or reservoir that
allows water passage into another country. The country
upstream could potentially cause a drought for their
neighboring country either intentionally or inadvertently.

6. It’s Not Always Safe

Despite a lack of combustible fuel, dams still offer dangers of
their own. Construction accidents, as well as dam failure, can
result in injury or loss of life. The Hoover Dam claimed as many
as 112 deaths during its construction, and one of the worst
catastrophes occurred when the Banqiao Reservoir Dam in
China was destroyed by a typhoon in 1975.

OR
1. Impact on Fish

To create a hydro plant, a running water source must be

dammed. This prevents fish from reaching their breeding
ground, which in turn affects any animal that relies on those
fish for food.

As the water stops flowing, riverside habitats begin to

disappear. This can even remove animals from accessing water.

2. Limited Plant Locations

While hydropower is renewable, there are limited places in the

world that are suitable for plant construction. On top of this,
some of these places are not close to major cities that could
fully benefit from the energy.

3. Higher initial Costs

While no power plant is easy to build, hydro plants do require

you to build a dam to stop running water. As a result, they cost
more than similarly sized fossil fuel plants.

Although, they will not need to worry about purchasing fuel

later on. So it does even out over the long-term.

4. Carbon and Methane Emissions

While the actual electricity generation in the plant does not

produce emissions, there are emissions from the reservoirs
they create. Plants that are at the bottom of a reservoir begin
to decompose. And when plants die, they release large
quantities of carbon and methane.

5. Susceptible to Droughts
While Hydropower is the most reliable renewable energy
available, it is dependent on the amount of water in any given
location. Thus, the performance of a hydro plant could be
significantly affected by a drought. And as climate change
continues to heat up or planet, this could become more
common.

6. Flood Risk

When dams are built at higher elevations, they pose a serious

risk to any town nearby that is below it. While these dams are
built very strong, there are still risks. The biggest dam failure in
history is the Banqiao Dam failure. Due to excess rainfall from a
typhoon, the dam collapsed. This resulted in the deaths of
171,000 people.

Hydro Power Plant Layout

In hydro power plant, the energy of water is used to move the

turbines which in turn run the electric generators. The energy
of the water used for power generation may be kinetic or
potential. The kinetic energy of water is its energy in
movement and is a function of mass and velocity, while the
potential energy is a function of the difference in level per head
of water between two points.

In either case, continuous availability of water is a basic

necessity, to ensure this, water collected in natural lakes and
reservoirs at high altitudes may be used or water may be stored
by constructing dams across flowing streams.

Hydro-power is a conventional renewable source of energy

which is clean, free from pollution and generally has a good
environmental effect, but it requires a large investment and
involves increased cost of power transmission.
Hydro power plants are developed for the following
purposes :

1. Generation of electricity at low cost.

2. To control the floods of the rivers.
3. Is to store the water for drinking and irrigation.
4. To develop the surrounding area.

Water is the naturally available renewable source of energy.

The power generation from a hydro-electric power plant is
clean and free from pollution, generally, it has a good
environmental impact.

The main aim of a hydro-electric power plant is to harnessing

power from water flowing under pressure. Nearly 30 to 35% of
the total power generation of the world is met by a
hydro-electric power plant.

Hydro-power plants are also developed for their following

advantages:

1. To control the floods of the rivers.

2. Is to develop the irrigated lands.
3. To have storage of drinking water.
4. The running cost of these plants is very low compared to
other power plants.
5. Greater control over the turbines,
6. High reliability compared to other plants.
7. Absolutely no fuel charges.
8. The load can be varied quickly as per the changing
demand.
9. These plants have no disposal problem
10. These plants have no environmental problems.
Storage and Pondage:

During the rainy season, when the stream is in floods it carries

a huge quantity of water as compared to the stream in other
times of the year i.e. the quantity of water carried by it is very
less. However, the demand for power normally does not match
such variation of the natural flow of the stream.

Therefore, some arrangement in the form of storage and

pondage of water is required for the proper handling of the
flow of water so as to make it available in important quantity to
meet the power demand at a given time.

The storage may be defined as the impounding of a

considerable amount of excess runoff during seasons of surplus
flow for use in dry seasons. This is achieved by constructing a
dam across the stream at a suitable site and building a storage
reservoir on the upstream side of the dam.

The pondage may be defined as a regulating body of water in

the form of a relatively small pond or reservoir provided at the
plant. The pondage is used to regulate the variable water flow
to meet power demand. It helps in short term variations which
occur due to:

 Sudden rise or drop in load on the turbine.

 Sudden changes in the inflow of water.
 Change of water demand by turbines and the natural flow
of water from time to time.
The turbines are required to meet the power demand higher
than the average load when the pondage supplies the excess
quantity of water required during that period.

Pondage increases the capacity of a river over a short time,

such as a week.Storage, however, increases the capacity of a
river over an extended period of 6 months to as much as 2
years.

Factors to be considered for Selection of Site for HydroPower

Plant:

Following factors should be considered while selecting the site

for hydro-power plant :

1. Availability of water: Large quantity of water should be

available throughout the year at the proposed site.
2. A requirement of head flow availability and storage
capacity.
3. The character of foundation, particularly for the dams.
4. The land should be cheap and rocky.
5. The topography of the surface at the proposed location.
6. Accessibility of the site i.e. the site should have
transportation facilities like road and rail.
7. Nearness to the load centre.
8. Availability of the materials for the construction.
9. Arrangement and type of dam, intakes, conduits, surge
tank and powerhouse.
10. Cost of project and period required for completion.
11. Impacts of water pollution.

Hydropower Plant Layout

It consists of the catchment area, reservoir, dam, slice gate or

valve, surge tank, penstock, inlet valve, turbine, draft tube,
powerhouse equipment, tailrace, etc.

The collected water from the reservoir is supplied from the

dam through slice gate, penstock, inlet valve to the turbine. The
turbine converts the potential energy of the water into
mechanical energy to run the generator. The generator
produces electric power. After doing the work water flows into
the tailrace through draft tube.

Components for Hydro Power Plant Layout:

Following are the essential components of the hydro-power

plant :

1. Catchment area
2. Reservoir
3. Dam
4. Spillways
5. Penstock
6. Surge tanks
7. Prime movers
8. Draft tubes
9. Powerhouse and equipment.

1. Catchment Area

The whole area behind the dam draining into a stream or river
across which the dam has been built at a suitable place is called
catchment area.

2. Reservoir

It is the area where the water is stored and utilized for power
generation. A reservoir may be natural or artificial.

A natural reservoir is a lake in high mountains. An artificial tank

is built by erecting a dam across the river.

3. Dam

A dam is a barrier built across the river to store the water for
power generation. Dams are built of concrete or stone masonry,
earth or rockfill. The dam stores the water one side and on the
other side, it is having a powerhouse to generate the power.

4. Spill Ways

It is a safety valve for a dam. It is provided to discharge the

excess water from the dam to safeguard the dam against
floods.

5. Conduits

It is a pipe connected between surge tank and prime mover,

usually, these are of steel-reinforced concrete pipes.

6. Surge Tank

There is a sudden increase in pressure in the penstock due to

the sudden decrease in the rate of water flow to the turbine
when the gates admitting water to the turbines are suddenly
closed owing to the action of the governor.

This happens when the load on the generator decreases. This

sudden rise of pressure in the penstock above normal due to
reduced load on the generator is known as “water hammer”.

A surge tank is a small reservoir employed between dam and

powerhouse nearer to the powerhouse to reduce the pressure
swings in the penstock by allowing the excess water to enter
into the surge tank during low load periods and the stored
water can be supplied to the penstock during high load periods.

7. Prime Mover

These are the turbines used to convert the kinetic energy of the
water into mechanical energy to produce electric energy.
8. Draft Tube

It is a diverging discharge passage connected to the tailrace. It

supports the runner for utilizing the remaining kinetic energy of
the water at the discharge end of the runner.

9. PowerHouse

A powerhouse consists of two main parts, a substructure to

support the hydraulic and electric equipment such as turbines,
generators, valves, pumps, governors, etc., and superstructure
to house and protects these types of equipment.

Types of Hydropower Plant with Layout

Different types of hydropower plant can be classified as

follows:

1. According to the availability of head

1. High head power plants
2. Medium head power plants
3. Low head power plants.
2. According to the nature of the load
1. Base load plants
2. Peak load plants.
3. According to the availability of water
1. Runoff river plant without pondage
2. Runoff river plant with pondage
3. Storage type plants
4. Pump storage plants
5. Mini and micro-hydel plants.

Base Load Plants

This types of power plant work independently and supply the

power to the whole load. This plant takes the load on the base
portion of the load curve. The load on the plant remains more
or less uniform during the operation period. It works for the
whole time i.e. it supplies the power when there is a
requirement.

Baseload plants are generally large in capacity. The run-off-river

and storage type plants are used as baseload plants. The load
factor for such plants is considerably high.

Peak Load Plants

The peak load plants are designed for taking care of peak loads
of the demand curve. Run-off river plant with pondage and
pumped storage plants are generally used as peak load plants.
These plants supply the power to the load premises when there
is a peak load period only. Rest of the time the power is
supplied by the main plant.

In this type of plants, the main power plant is always required

and hydro power plant works as secondary plant and shares
the load of two to three hours. In case of runoff river hydro
plants with poundage, a large pound is essential and extensive
seasonal storage is usually provided.

These power plants have large seasonal storage and relatively

high heads and are likely to be located on small watersheds.
They store the water during off-peak period and supply during
peak periods on the top of the load curve. The load factor of
peak load plants is considerably low compared with baseload
plants.

Runoff River Plants

A runoff river may be classified into two types:

1. Runoff river plant without pondage

2. Runoff river plant with pondage.
A runoff river plant without pondage. This plant does not store
the water and uses the water as it comes. There is no control
on the flow of water so that during high floods or low loads
water is wasted while during low run-off the plant capacity is
considerably reduced.

Due to non-uniformity of supply and lack of assistance from a

firm capacity the utility of these plants is much less than those
of other types. The head-on which these plants work varies
considerably. During good flow conditions, these plants may
cater to the baseload of the system, when flow reduces they
may supply the peak demands.

Runoff river plant with pondage uses storage of water behind a

dam at the plant and increases the stream capacity for a short
period, say a week. Storage means a collection of water in
upstream reservoirs and this increases the capacity of the
stream over an extended period of several months.

The storage plants may work suitably as baseload and peak

load plants. This type of plant compared to without pondage, is
more reliable.

Storage Type Plant (Reservoir Type)

A storage-type plant is one with a reservoir of sufficiently large

size to permit carry-over storage from the wet region to the dry
region, and therefore water supply is substantially constant and
more than the minimum natural flow of the water.

This plant can be used as baseload plant as well as peak load

plant as water is available with control when required.

It consists of a reservoir, a dam with penstock, powerhouse

arrangements. The powerhouse is placed at the toe of the dam.
The water is allowed to store in a reservoir from the river or
lakes in sufficient quantity.

The water flows from the dam through the penstock when
cresh gate is opened to the powerhouse. In powerhouse water
with high pressure enters into the turbine to generate power.
After doing the work water is allowed to flow to the tailrace. A
Pelton wheel is the common prime mover used in such power
plants.

Pumped Storage Plants

The pumped storage plants are used at the places where the
quantity of water available for power generation is low. Here
the water passing through the turbine is stored in “tailrace
pond”. During the low load periods, this water is drawn back to
the head reservoir applying the extra energy available.

This water can be reused for generating power during peak

load periods. The pumping of water may be done seasonally or
regular depending upon the conditions of the site and the
nature of the load on the plant.

The simple construction of the stored hydro-power plant. It

consists of headwater pond and dam, penstock connected
power house with pumps and turbines and trail race pond with
the dam. The water from head water pond is supplied to the
power house through the penstock, where turbines are rotated
for power generation.

From the turbine, the water is discharged into the tailrace pond.
The water stored in the tailrace pond is pumped back to the
head reservoir with the help of the pump during low load
periods. This water is again used for power generation during
peak load periods.
Such plants are usually interconnected with steam or diesel
power plants so that off-peak capacity of interconnecting
stations is used in pumping water and the same is used during
peak load periods.

Advantages of Pumped Storage Power Plants

1. There is a substantial increase in peak load capacity.

2. Increased operating efficiency.
3. It can be used as both base loads plant and peak load
plant.
4. Load the plant remain uniform.
5. Improved load factor.

Mini and Microhydel Plants

The hydro power plants working with 5 m to 20 m head are

known as mini hydel plants and the hydel power plants working
with the heads less than 5 m head are known as micro hydel
plants. These plants can generate power ranging from 100 KW
to 5 MW with a period of one and half year.

These plants having a small reservoir with the dam and small
capacity power house using bulb turbines with straight
diverging tube acts as a draft tube. The water flows from a
small reservoir through the small penstock into the turbine in
power house and generates the power. After generating the
power the water is discharged into the tailrace through draft
tube.

Micro-hydel plants make use of standardised bulb sets with

unit output ranging from 100 to 1000 KW working under heads
between 1.5 to 5 m.
Advantages of Hydro-electric Power Plant

Following are the advantages of a hydro-electric power plant:

1. Low operating cost compared to a thermal power plant.

2. The cost of generation is unaffected by the load factor.
3. No fuel charges.
4. High useful life of about 100 – 125 years.
5. Low maintenance cost compared to the thermal power
plant
6. Highly reliable.
7. It can be started quickly and synchronize the plant.
8. There is no problem with fuel and ash handling.
9. No nuisance of smoke exhaust gases and soots.
10. No health hazards due to air pollution.
11. It has no standby losses.
12. The machines used in hydel plants are robust and no
problem of high temperature and pressure.
13. The efficiency of the hydel plant does not change with
age.
14. The number of operations required is considerably small.
15. It can serve the purpose of flood control and stored water
can be used for drinking and irrigation work.
16. Less labour is required to operate the plant.

Disadvantages of Hydro-electric Power Plant

Following are the disadvantages of a hydro-electric power

plant:

1. High capital cost.

2. Power generation only dependent on the quantity of
water availability.
3. It takes a considerably long time for the construction
 4. Site of the hydro-electric power station is always away
from the load centre, therefore transmission cost becomes
high.
5. Sometimes isolated sites are difficult to access.

Pondage

Pondage usually refers to the comparably small water storage

behind the weir of a run-of-the-river hydroelectric power
plant. Such a power plant has considerably less storage than
the reservoirs of large dams and conventional hydroelectric
stations which can store water for long periods such as a dry
season or year. With pondage, water is usually stored during
periods of low electricity demand and hours when the power
plant is inactive, enabling its use as a peaking power plant in
dry seasons and a base load power plant during wet
seasons.] Ample pondage allows a power plant to meet
hourly load fluctuations for a period of a week or more.

Types of Hydropower Plants

There are three types of hydropower facilities: impoundment,
diversion, and pumped storage.

Some hydropower plants use dams and some do not.

Although not all dams were built for hydropower, they have
proven useful for pumping tons of renewable energy to the grid.
In the United States, there are more than 90,000 dams, of
which less than 2,300 produce power as of 2020. The other
dams are used for recreation, stock/farm ponds, flood control,
water supply, and irrigation.

Hydropower plants range in size from small systems suitable

for a single home or village to large projects producing
electricity for utilities.

IMPOUNDMENT

The most common type of hydroelectric power plant is an

impoundment facility. An impoundment facility, typically a
large hydropower system, uses a dam to store river water in a
reservoir. Water released from the reservoir flows through a
turbine, spinning it, which in turn activates a generator to
produce electricity. The water may be released to meet
changing electricity needs or other needs, such as flood control,
recreation, fish passage, and other environmental and water
quality needs.

DIVERSION

A diversion, sometimes called a “run-of-river” facility, channels

a portion of a river through a canal and/or a penstock to utilize
the natural decline of the river bed elevation to produce energy.
A penstock is a closed conduit that channels the flow of water
to turbines with water flow regulated by gates, valves, and
turbines. A diversion may not require the use of a dam.

PUMPED STORAGE

Another type of hydropower, called pumped

storage hydropower, or PSH, works like a giant battery. A PSH
facility is able to store the electricity generated by other power
sources, like solar, wind, and nuclear, for later use. These
facilities store energy by pumping water from a reservoir at a
lower elevation to a reservoir at a higher elevation.

When the demand for electricity is low, a PSH facility stores

energy by pumping water from the lower reservoir to an upper
reservoir. During periods of high electrical demand, the water is
released back to the lower reservoir and turns a turbine,
generating electricity.

SIZES OF HYDROELECTRIC POWER PLANTS

Hydropower facilities range in size from large power plants,

which supply many consumers with electricity, to small and
even ‘micro’ plants, which are operated by individuals for their
own energy needs or to sell power to utilities.

Large Hydropower

Although definitions vary, DOE defines large hydropower

plants as facilities that have a capacity of more than 30
megawatts (MW).

Small Hydropower

Although definitions vary, DOE defines small hydropower

plants as projects that generate between 100 kilowatts and 10
MW.

Micro Hydropower

A micro hydropower plant has a capacity of up to 100 kilowatts.

A small or micro hydroelectric power system can produce
enough electricity for a single home, farm, ranch, or village.
 Dams
A dam is a structure built across a stream or river to hold water
back. Dams can be used to store water, control flooding, and
generate electricity.

A dam is a barrier that restricts or stops the flow of water,

helps suppress floods, as well as providing irrigation, industrial,
and aquaculture uses. Here are seven of the different kinds of
dams :
1. Diversion Dam
2. Buttress Dam
3. Embankment Dam
4. Cofferdam
5. Storage Dam
6. Detention Dam
7. Gravity Dam

1) Diversion Dam
Like the name says, a diversion dam is used to divert water.
They provide pressure to push water into ditches, canals, or
other areas used for conveyance. Diversion dams are typically
lower in height and have a small water storage area in it’s
upstream.
2) Buttress Dam
Buttress dams can take many forms, but they all consist of a
sloping deck supported by intervals of buttresses. There are
three main buttress dams, including: multiple arch type,
massive head type, and deck type. Buttress dams usually use
less concrete than other dams but are not necessarily cheaper.
3) Embankment Dam
An embankment dam is a large, artificial dam that is
constructed with natural excavated materials or industrial
waste materials, such as compacted plastics, and various
compositions of soil, sand, rock, and clay.
4) Cofferdam
A cofferdam is a temporary, portable dam used for a variety of
projects including bridge repair, shoreline restoration, pipeline
installation, and many other construction projects. A cofferdam
is used to close off some or all of a construction area.
5) Storage Dam
These dams are not mean to divert or keep water out, but to
keep water in. Storage dams are constructed to store water
during the rainy seasons, supply water to the local wildlife, and
store water for hydroelectric power generation, and irrigation.
Storage dams are the most common types of dams.
6) Detention Dam
Detention dams are specifically constructed for flood control by
retarding flow downstream, helping reduce flash floods (to
some extent). The water is retained in a reservoir to be later
gradually released.
7) Gravity Dam
A gravity dam is a massive, man-made concrete dam designed
to hold large volumes of water. Because of the heavy concrete
used, it is able to resist the horizontal thrust of the water, and
gravity essentially holds the dam to the ground. They are used
to block rivers in wide valleys and must be built on a strong
foundation of bedrock.

Dams are said to be an important source of water supply and

high importance for various other reasons. They supply the
water for the various means including domestic use, irrigation
purposes and also for the industrial uses.

Dams are also involved in the hydroelectric power generation

and in the river navigation. The application of these dams is
much more important in daily activities including cooking,
cleaning, bathing, washing, drinking water, for the gardening
and for the cultivation purpose.

The big dams and the reservoirs also provide recreational

areas for the purpose of fishing and also boating. They also
cater the insecurity needs of humans by reducing or by
preventing the floods. During the times of excess flow of water,
the dams store the water in the reservoir; later they release
that water during the times of low flow, also when the natural
flows of water are inadequate to meet the demand.

Advantages of Dams
Advantages of dams are numerous, that is the reason so much
money and work goes into building and maintaining them.
Some of the advantages are:

 Electricity is produced at the constant rate with the help

of hydroelectricity or hydroelectric power.
 If there is no need for electricity, then the sluice gates can
also be closed or stopping the generation of electricity.
Water can also be saved for the use of another time as
and when the demand for electricity is high hence the
usage of water remains judicious.
 Dams are so designed by well-qualified engineers to span
many of the decades and also can contribute to the
generation of electricity for about many years or even
decades to come.
 The lake or reservoir which forms behind the dam can
also be used for the irrigation purpose, water sports or
even as other forms of pleasurable activities.Few large
 dams such as the Bhakra Nangal dam present in India is
the tourist attractions.
 The buildup of water inside lake means that the energy
can also be stored when needed and also when water is
released for producing the electricity.
 When used, the produced electricity by the dams does
not even produce the greenhouse gases and also hence
they do not pollute the atmosphere.

List of the Disadvantages of Dams

1. Dams can displace a significant number of people.

An estimated 500 million people have been displaced by dams
in the last two centuries because of the reservoirs that form
behind each structure. As the surrounding dry areas get
flooded, we no longer have the option to use land that was
previously accessible for a variety of purposes. That means
local agricultural activities go through a disruption process,
even though the eventual increase in available water supports
more irrigation.

2. Reservoirs behind a dam can lead to higher greenhouse gas

emissions.
When vegetation gets engulfed in water, then the plants will
eventually die. When this outcome occurs, the dead organic
material releases methane that ultimately makes its way into
the atmosphere. The increase in the production of greenhouse
gases is significant because methane is up to 20 times more
potent as a reflector than carbon dioxide.

The use of a dam in certain areas can also contribute to the loss
of forests. When we lose a significant number of trees
simultaneously, then there is a corresponding uptake of carbon
dioxide that occurs because there are fewer photosynthesis
processes happening each day.

3. This technology disrupts local ecosystems.

Dams create a flooding issue behind the structure as a way to
form a reservoir. Not only does this disrupt human activities,
but it also destroys the existing wildlife habitats that exist. This
issue can disrupt entire ecosystems, which can have an adverse
effect on a whole regional biome. Marine life that relies on an
unobstructed flow of a river, such as migratory fish, can be
adversely affected by the decision to dam the water.

4. Some river sediment is beneficial.

Dams can have a profound impact on the overall aquatic
ecosystem of a region. The transformation upstream creates a
lack of settlement that moves down the waterway to support
the entire marine habitat. It can also cause changes in
temperature, chemical composition, and shoreline stability.
Many reservoirs also host invasive species, such as algae or
snails, that undermine the natural communities of the plants
and animals that lived on the river before.

The riverbeds that are downstream from a dam can erode by

several yards within the first decade of operations. This damage
can extend for hundreds of miles downstream afterward.

5. Dams create a flooding risk if they experience a failure.

We might use dams to provide us with a form of flood control,
but the failure of this structure can have devastating
consequences for downstream communities. The Vajont Dam
Failed in 1963, only 4 years after its construction was finalized
just outside of Venice, Italy. A landslide during the initial filling
triggered a tsunami in the reservoir, causing over 50,000,000
cubic meters of floodwater that impacted nearby towns and
villages. Some reports say that the wave was over 820 feet
high.

Almost 2,000 people died in this disaster, and it was all because
the dam was located in a geologically unstable area. When the
Banqiao Reservoir Dam failed in 1975 in China, it caused an
estimated 171,000 deaths.

6. Dams can have an adverse impact on the groundwater

table.
When riverbeds experience deepening, then this problem
creates a lower groundwater table along the river. That means
it is more challenging for plant roots to reach what is required
for survival. Homeowners in the vicinity must also dig deeper
wells to draw water for their households. This issue can even
change the mineral content and salts found in the fluid,
creating damage to soil structures along the way.

7. The construction of a dam is a costly investment.

A large dam is defined as a structure that is higher than 15
meters. This definition means there are more than 57,000
structures around the world. Major dams are over 150 meters
tall, and there are over 300 of these. China has the most, with
over 23,000 operational facilities. The United States is in
second, but far behind at 9,200. The cost of a large dam today
can be over $20 billion, and it may take between 7 to 10 years
to complete its construction. Those are resources that many
communities could put to better use.

8. Dams can block water progression to different states,

provinces, and countries.
When a dam gets built at or near a border between two states,
provinces, or countries, then it might also block the progress of
the water in one of those areas. That means the supply from
the same river in the neighboring country is no longer under
their direct control. This disadvantage can result in severe
issues between neighbors, creating a constant source of
conflict that can sometimes even lead to war.

9. It can make the water too shallow for navigation.

Dams try to avoid environmental impacts by releasing water
downstream and creating marine life channels that allow for
upstream movement. Although this approach is imperfect, the
updates to this engineering process have had some benefits.
What doesn’t get solved through this process is the depth of
water that might be available downstream. The Colorado River
is an excellent example of this issue because the waterway
doesn’t make it to its outlet most years because of all the
damming activity that occurs.

If the waters are too shallow to use in a river, then there is no

way to use it for transportation benefits. This issue also
changes the settlement profile so that marches and wetlands
no longer receive the healthy supports from the river that they
need.

10. Reservoirs can be challenging to maintain.

When drought is a significant issue for a community, then a
reservoir that’s behind a dam can be a vital resource.
Maintaining this new body of water comes with a set of its own
challenges because evaporation can happen during dry times
and result in an increase in environmental problems. There also
tends to be a significant buildup of organic matter in the
sediment with this disadvantage, resulting in potentially
carcinogenic trihalomethanes when the water gets chlorinated
for drinking purposes.
 Reservoir

A reservoir is an artificial lake where water is stored.

when a barrier is constructed across a river in the form of dam,

water gets stored on upstream side of the barrier, forming a
pool of water called dam reservoir or impounding reservoirs or
a storage reservoirs or a river reservoirs.

These are some common uses for reservoirs:

 Water supply
 Hydroelectric power
 Flood control
 Irrigation
 Navigation
They are also used to regulate the flow of water in rivers.
Water can be released from the reservoir during drier seasons
to support wildlife and the environment downstream, and to
provide a resource for human uses.

Reservoirs are mainly categorized into 2 types :

 Impounding ( into which a river flows naturally ).

 Service or Balancing.

Impounding Reservoirs

 Storage or Conservation Reservoir

It can retain excess supplies during period of peak flows and
can release them gradually during low flows when required. It
supplies water for useful purposes such as irrigation, power
generation, domestic, industrial and municipal supply.
  Detention Reservoir
In this type the water is stored for relative short period of time,
until the stream can safely carry the ordinary flow plus the
released water. Such reservoir usually have outlets without
control gates.

 Impounding or Storage Reservoir

A reservoir with gate-controlled outlets wherein surface water
retained for a considerable time and released for use at the
time when normal flow of the stream is insufficient to satisfy
the requirements. It is also called as the ‘Retarding Reservoir’

 Multipurpose Reservoir
It is constructed and equipped to provide storage and release
of water for two or more purposes such as irrigation, flood
control, power generation, etc. This reservoir would be
gradually emptied just before the arrival of monsoon rains
hoping that it would be filled to the brim at the end of the
flood.

Service Reservoirs

 Distribution Reservoir
It is connected with distribution system (water supply project),
used primarily to care for the fluctuations in demand which
occur over short period and as local storage in case of
emergency such as break in a main supply line.

 Balancing Reservoir
Downstream of the main reservoir for holding water let down
from the main reservoir in excess of that required for irrigation,
power generation or other purposes.

 Auxillury Reservoir
It is the reservoir which supplements and absorbs the spill of
the main reservoir.
Storage Zones and Control Levels of Reservoir

Full Reservoir Level ( FRL )

It includes both active and inactive storage and also flood

storage, if provided for. This is the highest reservoir level that
can be maintained without spillway discharge or through sluice
ways.

Minimum Draw-down Level ( MDDL )

It is the level below which the water will not be drawn down so
as to maintain a minimum head required in power projects.

Dead Storage Level ( DSL )

Below this level, there are no outlets to drain the water in the
reservoir by gravity. Below this level silt will get accumulated
during the design lifespan.

Maximum Water Level ( MWL)

The level that is ever likely to be attained during the passage of

the design flood. Sometimes called as high flood level ( HFL) or
high reservoir level ( HRL )

Live Storage

This is the volume of water actually available at any time

between the dead storage level and full supply level. The
minimum operating level must be sufficiently above the lowest
discharge outlet to avoid vortex formation and air entrainment.
Dead Storage

It is the total storage below the inverted level of the lowest

discharge outlet. It is not useful and cannot be used for any
purpose under ordinary operating condition.

Outlet Surcharge of Flood Storage

This is required storage between FRL and maximum water level

to contain the peaks of flood that might occur when there is
insufficient storage capacity for them below FRL.

Buffer Storage

This is the storage just above the dead storage level upto
minimum draw-down level. Release from this zones are made
in dry situation to cater for essential requirements only. Dead
storage and buffer storage together is called Inactive Storage.

Gravity Dam
Gravity dams are massive structure dam which is constructed
of concrete or stone masonry. These dams are hold by the
gravity to the ground.

A gravity dam depends on its own weight for stability and is

usually straight in plan although sometimes slightly curved.

A gravity dam can hold a large amount of water.

As they rely on their own weight, it is necessary to construct

them on a solid foundation of bedrocks.

A gravity dam may be constructed either of masonry or of

concrete.
Masonry gravity dams are nowadays constructed of only small
heights.

All major and important gravity dams are now constructed of

concrete only.

A gravity dam may be either straight or curved in plan.

A gravity dam is mostly straight in plan and is known as

‘straight gravity dam’. However, it may also be slightly curved
in plan.

A curved gravity dam resists the external forces by its weight

and not by arch action.

The most ancient gravity dam on record was built in Egypt

more than 400 years B.C. of un-cemented masonry.

Archaeological experts believe that this dam was kept in

perfect condition for more than 45 centuries.

Most of the gravity dams are solid, so that no bending stress is

introduced at any point and hence, they are sometimes known
as ‘solid gravity dams’.

A gravity dam, however, can be hollow and is known as ‘hollow

gravity dam’.

Gravity dams are particularly suited across gorges with very

steep side slopes where earth dams might slip.

Where good foundations are available, gravity dams can be

built up to any height. The highest dams in the world are of
gravity type.
Advantages of gravity dams.

There is no type of dam more permanent than one of the solid

concrete, nor does any other type require less for maintenance.
As compared to earth and rock-fill dams gravity dams have the
following advantages :

1. Gravity dams are relatively more strong and stable than

earth dams. They are particularly suited across gorges having
very steep side slopes where earth dam, if constructed, might
slip.

2. Gravity dams are well adapted for use as an overflow

spillway crest. Earth dams cannot be used as overflow dams.
Due to this, a gravity overflow dam is often used for the
spillway feature of earth and rock-fill dams.

3. They can be constructed of any height, provided suitable

foundations are available to bear the stresses.

The height of an earth dam is usually limited by the stability of

its slopes requiring a very wide base width. Highest dams in the
world are made of gravity dams only.

4. Gravity dam is specially suited to such areas where there is

likelihood of very heavy downpour. The slopes of earth dam
might get washed away in such a situation.

5. They requires the least maintenance.

6. The failure of this dam, if any, is not sudden. It gives enough

warning time before the area to downstream side is flooded
due to the damage of the structure.

On the contrary, an earth dam generally fails suddenly.

7. Deep-set sluices can be used in the gravity dams, to retard
the sedimentation or silt deposit in the reservoir. The trap
efficiency of a reservoir of an earth dam is more than that of a
reservoir of gravity dam.

8. They are cheaper in the long run since it is more permanent

than any other type. Thus the benefit-cost ratio of such a dam
is always higher.

Disadvantages of Gravity Dams.

The disadvantages of gravity dam, as compared to an earth

dam are as follows:

1. Gravity dams can be constructed only on sound rock

foundations. They are unsuitable on weak foundations or on
permeable foundations on which earth dams can be
constructed with suitable foundation treatment.

2. The initial cost of a gravity dam is always higher than an

earth dam. Hence, where funds are limited and where suitable
materials are available for the construction of an earth dam,
the earth dam may be preferred.

3. If mechanized plants, such as manufacturing and

transporting mass concrete, curing of concrete etc. are not
available, a gravity dam may take more time to construct.

4. They require skilled labor or mechanized plants for its

construction.

5. It is very difficult to allow subsequent rise in the height of a

gravity dam, unless specific provisions have been made in the
initial design.
Causes of failure of a Gravity Dam:

A gravity dam may fail in following modes:

1. Overturning of dam about the toe

2. Sliding – shear failure of gravity dam

3. Compression – by crushing of the gravity dam

4. Tension – by development of tensile forces which results

in the crack in gravity dam.

Spillway

A spillway is a structure used to provide the controlled release

of water from a dam or levee downstream, typically into the
riverbed of the dammed river itself. In the United Kingdom,
they may be known as overflow channels. Spillways ensure
that water does not damage parts of the structure not designed
to convey water.
Spillways can include floodgates and fuse plugs to regulate
water flow and reservoir level. Such features enable a spillway
to regulate downstream flow—by releasing water in a
controlled manner before the reservoir is full, operators can
prevent an unacceptably large release later.
Other uses of the term "spillway" include bypasses of dams and
outlets of channels used during high water, and outlet channels
carved through natural dams such as moraines.
Water normally flows over a spillway only during flood periods,
when the reservoir has reached its capacity and water
continues entering faster than it can be released. In contrast,
 an intake tower is a structure used to control water release on
a routine basis for purposes such as water supply
and hydroelectricity generation.

Here are some of the different types you may see:

 Overflow spillways
 Side Channel spillways
 Shaft spillways

Surge tank

A Surge tank is a water storage device used as a pressure

neutralizer in hydropower water conveyance systems in order
to dampen excess pressure variance.
A surge tank (or surge drum or surge pool) is a standpipe or
storage reservoir at the downstream end of a closed aqueduct,
feeder, dam, barrage pipe to absorb sudden rises of pressure,
as well as to quickly provide extra water during a brief drop in
pressure.
In mining technology, ore pulp pumps use a relatively small
surge tank to maintain a steady loading on the pump.
For hydroelectric power uses, a surge tank is an additional
storage space or reservoir fitted between the main storage
reservoir and the power house (as close to the power house as
possible). Surge tanks are usually provided in high or
medium-head plants when there is a considerable distance
between the water source and the power unit, necessitating a
long penstock. The main functions of the surge tank are: 1.
When the load decreases, the water moves backwards and gets
stored in it. 2. When the load increases, additional supply of
water will be provided by surge tank.
In short, the surge tank mitigates pressure variations due to
rapid changes in velocity of water.

Functions of Surge Tanks

The important functions of surge tank are as follows

 It should Protects the conduit system from high internal

pressures.
 It should help the hydraulic turbine regarding its
regulation characteristics.
 It should store the water to raise the pressure in pressure
drop conditions.

Location of Surge Tanks

The location of surge tank is also important to produce better

results. It should be located in such a way that

 Surge tanks are located near to the power house to

reduce length of penstocks.
 No limitations regarding surge tank height.
 Location at which flat sloped conduit and steep sloped
penstock meets.
Types of Surge Tanks

Various types of surge tanks used in the hydropower water

conveyance system are as follows.

 Simple surge tank

 Gallery type surge tank
 Inclined surge tank
 The restricted orifice surge tank
 Differential surge tank

1.Simple surge tank:

Simple surge tank has a vertical pipe that is linked between the
pen stock and the turbine generator.

They are built with greater height and also provide support for
holding the tank.

Whenever the speed of the water increases rapidly, the excess

water is stored in the resistance tank.

The top of the surge tanks is opened to the environment, if the

surge tanks are totally filled then this pressure is overtaken to
take care of neutralization.

2.Gallery type surge tank:

Gallery surge tank has additional storage galleries also known

as expansion rooms, so it is also called growth room surge
tanks.

These growth rooms are often provided on the backside and

prime levels.
At the bottom of the tank, level chambers are used to store
excess water, when needed or run with a slight drop in
pressure.

The chambers on the upper-pressure level are used to absorb

the extra pressure.

3.Sloping surge tank:

In sloping surge tank, the tank is provided with certain tilt.

The over-pressure enters the tilted tanks by providing tilted

surge tanks with overflow water and the pressure is dissipated.

4.Restricted Orifice Surge Tank:

Restricted orifice surge tank has orifice between the pipeline

and tank.

This drain is called throttle, so it is also called throttle surge

tanks and this throttle or hole has a small diameter.

If water overflows it should enter the tank through this orifice.

5.Differential surge tanks:

In this tank, an internal riser is installed within the tank.

This riser has a very small diameter through which the water
leaks; there are annular docks when the reduction in the riser is
over.

Advantages of Surge Tank:

 Surge tank reduces detecting potential problems like

vortex flow or waterfall.
  It provides proofing the safety against outflow from the
aeration structure.
 Also, used in the measurement of throttle loss.
 It has a low cost of computation time.
 They have verification of variants.
 The possibility of multi-phase simulation.
Disadvantages of Surge Tank:

 The surge tank has no simulation for wind behavior.

 Also has no simulation for water hammer.
 Time-consuming calculation and evaluation.
 Calibration required.

Water Hammer
Water hammer is a phenomenon that can occur in any piping
system where valves are used to control the flow of liquids or
steam. Water hammer is the result of a pressure surge, or
high-pressure shockwave that propagates through a piping
system when a fluid in motion is forced to change direction or
stop abruptly. This shockwave is also commonly referred to as a
hydraulic shock or hydraulic surge, and may be characterized
by a marked banging or knocking sound on the pipes
immediately after shutoff.
Water hammer can occur when an open valve suddenly closes,
causing the water to slam into it, or when a pump suddenly
shuts down and the flow reverses direction back to the pump.
Since water is incompressible, the impact of the water results
in a shock wave that propagates at the speed of sound
between the valve and the next elbow in the piping system or
within the column of water after the pump.
 The Effects of Water Hammer
The long-term effects of water hammer can include:

 Pump and Flow System Damage

Repeated water hammer may also cause significant damage to
pumps, existing valves, and instruments, lead to the
catastrophic failure of gasketed joints and expansion joints, and
affect the integrity of pipe walls and welded joints.

 Leaks
Water hammer can damage fittings, joints, and connections,
resulting in leaks. These leaks often start slowly, gradually
increasing in intensity over time. Smaller leaks may go
unnoticed for quite some time, leaving surrounding equipment
susceptible to damage.

 Ruptured Pipes
Ruptured pipelines due to pressure spikes are especially
expensive to repair. Rupture results in local pipeline failure and
can cause the entire system and other equipment to fail. The
ensuing damage can be extensive, often entailing major
replacement operations.

 External Property Damage

If left unchecked, water leaks can damage electrical equipment
and or lead to the corrosion of equipment or infrastructure.

 Accidents
Pipeline rupture can also endanger the health and safety of
employees and maintenance personnel. Depending on the
industry and specific facility, unmanaged leaks can also increase
the risk of slips, falls, and electrocution.
 Downtime/Maintenance
Property damage can lead to costly repairs or equipment
replacements. Additional financial losses may also be incurred
due to downtime required for additional maintenance, repairs,
or installations

Preventing Water Hammer

One of the main contributors of water hammer can be the
choice of check valve type. Valve types, such as swing, tilting
disc or piston style check valves, depend on gravity and the
reversal of flow to return the valves to the closed position. This
causes water to slam into the valve mechanism, creating a
pressure wave that propagates through the piping system.
Silent or spring-assisted check valves, on the other hand, are
fitted with an internal spring that silently moves the valve into
closed position before flow reversal, thereby reducing or
eliminating the possibility of water hammer.
Air chambers are also an effective water hammer solution.
These systems consist of a short segment of pipe, usually in the
form of a tee-fitting, with an empty/air-filled chamber that
serves as a cushion (shock absorber) for the water to expand
when it changes direction suddenly. This reduces the
magnitude of shock that would otherwise be directed towards
the pipeline.
Other effective methods for preventing water hammer include:

 Flushing old systems

 Installing pressure reducers and regulators in the supply
line
 Reduce operating pressure
 Invest in piping systems that feature air chambers as part
of the design
 Reduce pressure severity with silent check valves

Draft Tube

A draft tube is an integral part of a turbine. It helps to get water

from the reaction turbines smoothly.
A draft tube is a type of tube that connects the exit of the
water turbine to the tailrace. The tailrace is the water channel
that takes the water out of the turbine. It is usually located at
the outlet or exit of the turbines and converts the kinetic
energy of the water at the outlet of the turbine to static
pressure. The materials used to create a draft tube are cast
steel and cemented concrete

The principal purpose of the draft tube is to convert water

kinetic energy into pressure energy. To decrease the velocity of
the water and to raise the pressure of the water before joining
the tailrace, the pipe is used to steadily increase the
cross-sectional area. The draft tube raises the water pressure
to the atmospheric pressure. To tolerate the high pressure and
speed of the water, the tube must be strong enough.

Types of Draft Tube

Various forms of draft tubes are available. There are mainly 4

types of draft tube, and those are:

1. Conical draft tube

2. Simple elbow draft tube
3. Moody spreading draft tube
4. Elbow draft tube with a varying cross-section

conical draft tube

In this type of draft tube form, the flow direction is straight and
divergent. This tube style is made of mild steel plates. It is
tapered in shape and the outlet diameter is greater than the
inlet diameter of the draft tube. The tapered angle of the draft
tube should not be too wide to induce a divergence of the flow
from the wall of the draft tube. This angle should also not be
too short, since it would require a longer draft tube that brings
a substantial loss of kinetic energy. So, the angle of the taper is
still almost 10 degrees.

Simple Elbow Draft Tube:

The shape of the tube is like an elbow in a simple Elbow draft

Tube. It is used in the Kaplan turbine. In this type of draft tube,
the cross-section area remains the same for the entire length of
the draft tube. The inlet and outlet of the draft tube are circular.
This draft tube is used at low head positions and the turbine is
to be mounted next to the tailrace. It helps to minimize the
expense of drilling and the exit diameter should be as wide as
possible to recover kinetic energy at the runner outlet. This
tube has a moderate efficiency of around 60%.

moody draft tube

The outlet of the draft tube is split into two sections in this
form of the draft tube. Moody draft tube is similar to a conical
draft tube and is with a central core component that divides
the outlet into two parts. There are one inlet and two exits for
the draft tube. The main aim of this type of draft tube is to
reduce the swirling motion of water. The efficiency of this type
of tube design is almost 88%.

Elbow draft tube with varying cross-section:

An elbow draft tube with varying cross-section is an

improvement of a simple elbow draft. The inlet is circular and
the outlet is rectangular in this type. In general, the horizontal
section of the draft tube is inclined up to avoid air from
approaching the exit area. This type of tube varies in its
cross-section from inlet to outlet. The outlet is still beneath the
tailrace. The performance of this type of draft tube is used with
the Kaplan Turbine at about 70%.

Draft tube function

The primary function of the draft tube is to control the flow of

water. The turbine has a tailrace. The turbine is attached to this
tailrace by the tube, causing the turbine to be beyond the
water but still have access to the water. It requires the negative
head to be formed at the outlet of the runner and hence raises
the net head of the turbine. The turbine can be mounted above
the tailrace without any lack of net head and thus the turbine
may be adequately inspected.

Moreover, it transforms a significant portion of the kinetic

energy wasted at the outlet of the turbine into usable pressure
energy. Without a draft tube, the kinetic energy rejected at the
outlet of the turbine would be lost to the tailrace. The draft
tube stops the water from splashing out of the runner and
leads the water to the tailrace.

Advantages of Draft Tube

Some of the advantages of using the draft tube are:

1. Using the draft tube prevents the splashing of water from

the runner and leads the water to the tailrace.
2. The net turbine head is raised as the height is increased
between the turbine exit and the tailrace because of the use
of the draft tube.
3. The use of a draft tube greatly decreases the amount of
kinetic energy required at the tailrace.
4. The transfer of kinetic energy into pressure energy results
in a negative pressure head at the outlet of the turbine,
which serves to improve the total performance of the
turbine.

Draft Tube efficiency

The efficiency of the draft tube is the ratio of kinetic power

transfer to the kinetic energy available at the inlet to the draft
tube. The efficiency of a tube depends on how much of the
kinetic energy of the water is converted into pressure energy.
The more energy is converted, the more efficient the draft tube
can be.

Draft tube in Kaplan and Francis turbines?

In the case of Kaplan and Francis turbines (reaction turbines),

the head usable at the turbine inlet is usually low, so the
turbine is far closer to the tailrace to achieve the full head. As
much of the water’s pressure energy is converted into the
Turbine’s mechanical energy, the pressure at the outlet is lower
than the atmospheric pressure. Therefore, if water pressure is
less than the atmospheric pressure at the exit of the turbine,
then it induces the tail rushing water back into the turbine.

Today, the elevated pressure of water is significantly greater

than the atmospheric pressure. It solves the dilemma of the
water backflow from the tail to the turbine outlet. It should be
noted that the water flow back will do significant damage to
the turbine which can interrupt the turbine from working.

Francis Turbine

The Francis turbine is a reaction turbine

It is an inward flow reaction turbine that combines radial and

axial flow concepts. The Francis turbine is the most common
water turbine used today.

The Francis turbine operates a head range of 10 meters to

several hundred meters and is primarily used for electrical
power production.

The Main Parts of a Francis Turbine:

A Francis Turbine consists of the 5 main parts those are:

 Spiral Casing
 Stay Vanes
 Guide Vanes
 Runner Blades
 Draft Tube
Spiral Casing:

It provides an encased water path to contain the water

pressure.

The water flowing from the reservoir or dam is made to pass

through this pipe with high pressure. The blades of the turbines
are circularly placed, which means the water striking the blades
of the turbine should flow in the circular axis for efficient
striking. So, the spiral casing is used, but due to the circular
movement of the water, it loses its pressure.

To maintain the same pressure, the diameter of the casing is

gradually reduced, to maintain the pressure uniformly, thus
uniform momentum or velocity striking the runner blades.

Stay Vanes:

This guides the water to the runner blades.

Stay vanes remain stationary at their position and reduces the

swirling of water due to radial flow and as it enters the runner
blades. Hence, makes the turbine more efficient.

Guide Vanes:

Guide vanes are also known as wicket gates. The main function
or usages of the guide vanes are to guide the water towards
the runner. The water flow must be an angle and that is
appropriate for the design.

Runner Blades:

Absorbs the energy from the water and converts it to rotational

motion of the main shaft.
The runner blades design decides how effectively a turbine is
going to perform.

The runner blades are divided into two parts. The lower half is
made in the shape of a small bucket so that it uses the impulse
action of water to rotate the turbine.

The upper part of the blades uses the reaction force of water
flowing through it. These two forces together make the runner
rotate.

Draft Tube:

The draft tube is an expanding tube which is used to discharge

the water through the runner and next to the tailrace.

The main function of the draft tube is to reduce the water

velocity at the time of discharge.

Its cross-section area increases along its length, as the water

coming out of runner blades, is at considerably low pressure, so
its expanding cross-section area helps it to recover the pressure
as it flows towards the tailrace.

Kaplan Turbine

Kaplan Turbine is an axial reaction flow turbine and has

adjustable blades. When the water flows parallel to the axis of
the rotation of the shaft, the turbine is known as the axial flow
turbine.

And if the head of the inlet of the turbine is the sum of pressure
energy and kinetic energy during the flow of water through a
runner a part of pressure energy is converted into kinetic
energy, the turbine is known as reaction turbine.
For the axial flow reaction turbine, the shaft of the turbine is
vertical. The lower end of the shaft is made larger which is
known as a hub or boss. The vanes are fixed on the hub and
hence hub acts as a runner for the axial flow reaction turbine.

The Kaplan turbine was an evolution of the Francis turbine. Its

invention allowed efficient power production in the low head
application that was not possible with the Francis turbine.

Kaplan turbine is now widely used throughout the world

for high-flow, low head power production. The Kaplan turbine
is an axial flow reaction turbine because the water is moving in
the axial direction.

Main Parts of Kaplan Turbine:

A Kaplan Turbine is consisted of:

 Scroll casing,
 Guide vane mechanism,
 Hub with vanes or runner of the turbine, and
 Draft tube.

Scroll casing:

The scroll casing is a spiral type of casing that decreases the

cross-section area. First, the water from the penstocks enters
the scroll casing and then moves to the guide vanes.

From the guide vanes, the water turns through 90° and flows
axially through the runner.

The scroll casing protects the runner, runner blades, guide

vanes and other internal parts of the turbine from external
damage to the turbine.
Guide Vanes Mechanism:

This is the only controlling part of the whole turbine. which

opens and closes depending upon the demand of power
requirement.

When the more power output requirements, it opens wider to

allow more water to hit the blades of the rotor.

And when low power output requires, it closes to cease the

flow of water.

When the guide vanes are absent then the turbine cannot work
efficiently and so that the efficiency of the turbine decreases.

Hub with vanes or Runner of the turbine:

The term "Runner" in the Kaplan turbine plays an important

role. The runner is the rotating part of the turbine in which
helps in the production of electricity. The shaft is connected to
the shaft of the generator.

The runner of this turbine has a large boss on which its blades
are attached and the blades of the runner are adjustable to an
optimum angle of attack for maximum power output. The
blades of the Kaplan turbine have twist along its length.

Twist along its length in the Kaplan turbine is provided because

to have always the optimum angle of strike for all cross-section
of blades and hence to achieve greater efficiency of the
turbine.

Draft Tube:
At the exit of the runner of Reaction Turbine, the pressure
available here is generally less than the atmospheric pressure.
The water at the exit cannot be directly discharged to the
tailrace.

A tube or pipe is gradually increasing area and this is used for

discharging water from the exit of the turbine to the tailrace.

So, the increasing area of the tube or pipe is called a Draft tube.
One end of the draft tube is connected to the runner outlet and
the other end is submerged below the level of water in the
tail-race.

The main important point is that the Draft tube is used only in
the Reaction turbine.

There are 4 types of draft tube:

 Simple Elbow Draft Tube

 Elbow with the varying cross-section
 Moody Spreading Draft Tube.
 Conical Diffuser or Divergent Draft Tube

Advantages of the Kaplan Turbine:

The advantages of the Kaplan Turbine are listed below:

 This turbine work more efficiently at low water head and

high flow rates as compared with other turbines.
 This is smaller in size.
 The efficiency of the Kaplan turbine is very high as
compares with other types of hydraulic turbines.
 The Kaplan turbine is easy to construct and
 The space requirement is less.

Disadvantages of Kaplan Turbine:

Although there are some disadvantages of the Kaplan Turbine
and those are:

 The position of the shaft is only in the vertical direction.

 A large flow rate must be required.
 The main disadvantages are the cavitation process. which
occurs due to pressure drops in the draft tube.
 The use of the draft tube and proper material generally
stainless steel for the runner blades may reduce the
cavitation problem to a greater extent.

Applications of Kaplan Turbine:

Here are some applications of Kaplan Turbine:

 Kaplan turbines are widely used throughout the world for

electric power production. They cover the lowest head
hydro sites and are especially suited for high flow
conditions.
 Inexpensive microturbines are manufactured for
individual power production with as little as two feet of
head.
 Large Kaplan turbines are individually designed for each
site to operate at the highest possible efficiency, typically
over 90%.
 They are very expensive to design, manufacture and
install but operate for decades.

Governing of Hydraulic Turbines

 “The governing of a turbine is defined as the operation
by which the speed of the turbine is kept constant under all
working conditions (irrespective of the load variations).”
 The governing of a turbine is necessary as, a turbine is
directly coupled to an electric generator, which is required to
run at a constant speed under all fluctuating loads
conditions.
 It is done automatically by means of a governor, which
regulates the rate of flow through the turbines according to
the changing load conditions on the turbine.
 The governor used in hydraulic turbines should be very
strong as it has to deal with the water coming at a very large
force and huge quantity.

Difference of Pelton, Kaplan and

Francis Turbine

The basic difference between Pelton, Francis and Kaplan Turbines is

Sl.
Criteria Pelton Turbine Francis Turbine Kaplan Turbine
No

Pelton turbine is an Francis Turbine is Kaplan turbine is a

1 Type impulse type water an inward flow propeller type
turbine reaction turbine. reaction turbine.

The operating
It is used for high water head of a It is used for low
2 Head heads ranging from Francis turbine heads ranging from
250 to 1000m ranges from 40 10 to 70 metres
to 600m.

The diameter of The diameter of the

The diameter of the
the runner varies runner varies
3 Runner runner varies from
between 0.91 to between 2 to 11
0.8 to 0.6m
10.6 metres

Direction of The flow of water is The flow of The flow of water is

4
Flow of Water tangential to the water through axial through the
 Through the runner. Hence it is the blades blades.
Blades also called as combines both
tangential flow radial and axial
impulse turbines flow.

The power
The output power
Power Power generated is generated by a
5 obtained varies from
Generation about 400MW Francis turbine is
5 to 200 MW
about 800MW

The rate of speed in The speed of the

The rotational speed
a Pelton turbine turbine ranges
6 Speed varies from 69.2 to
changes from 65 to from 75 to
429 rpm.
800rpm 1000rpm

Medium
The required A Kaplan turbine
discharge is
Discharge discharge for the requires high
7 required for the
Required working of a Pelton discharge for
working of the
turbine is low. efficient working.
Francis turbine.

The Kaplan Turbine

The Francis
The Pelton turbines uses both kinetic
turbine converts
uses kinetic energy and potential
8 Type of Energy potential energy
and converts into energy, which then
into mechanical
mechanical energy is converted into
energy
mechanical energy.

The efficiency of a The efficiency of The Kaplan turbine

9 Efficiency Pelton turbine is a Francis turbine gives higher
about 85% is about 90%. efficiency about 90%

Features of Pelton, Kaplan and Francis

Turbine

Features of Pelton Turbines

 Pelton turbines are used where the water source has a

relatively high hydraulic head at low water flow rates.
 Pelton wheels can be designed for all sizes based on the
objective.
Features of Kaplan Turbines

The important applications of Kaplan Turbines are:

1. Electrical Power Production throughout the World.

2. Suitable for lowest head hydro sites and high flow
conditions.
3. Kaplan turbines can work with as little as 0.3m head at a
highly reduced performance given that sufficient flow
exists.
4. The design, manufacture, and installation is expensive but
can operate for decades.
5. Kaplan turbines designed individually for a site can give
the highest possible efficiency of around 90%.

Features of Francis Turbines

 The Francis turbines operate best when its casing is

completely filled with water at all times.
 It can be designed for a wide range of heads and flows.
 These turbines are not only used for electrical production,
but also for the pumped storage.

Hydro turbine
Hydro turbines are devices used in hydroelectric generation
plants that transfer the energy from moving water to a
rotating shaft to generate electricity. These turbines rotate or
spin as a response to water being introduced to their blades.
These turbines are essential in the area of hydropower - the
process of generating power from water.
Generally, the construction of turbines is the same. A row of
blades is fitted to some rotating shaft or plate. Water is then
passed through the turbine over the blades, causing the inner
shaft to rotate. This rotational motion is then transferred to
a generator where electricity is generated. There are a variety
of different types of turbines that are best used in different
situations. Each type of turbine is created to provide maximum
output for the situation it is used in.
The type of turbine selected for any given hydropower project
is based on the height and speed of the incoming water -
known as the hydraulic head - and the volume of water that
flows known as the hydroelectric discharge. Efficiency and cost
are also factors to be considered.

Hydro turbines can be classified based on how water flows

through the turbine itself. When passed through a turbine,
water can take a variety of different paths. This leads to three
categories of water flow through turbines:

 Axial Flow: Water flows through the turbine parallel to

the axis of rotation.
 Radial Flow: Water flows through the turbine
perpendicular to the axis of rotation.
 Mixed Flow: Water flows through in a combination of
both radial and axial flows. For example, in a Francis
turbine water flows in radially but exits axially.

Most hydro turbines tend to have mixed flows.

Pressure Change
Another criteria used to classify turbines is whether or not the
liquid pressure changes when flowing through a turbine. There
are two types of turbines that emerge from this classification,
explained below.
Impulse Turbine
In impulse turbines, the pressure of the liquid doesn't change in
the turbine itself. Instead, pressure changes occur only in the
nozzles that direct water flow to the turbine, while the turbine
itself operates at atmospheric pressure. These turbines are
composed of a jet nozzle or series of nozzles that direct water
to the blades of a turbine. Multiple nozzles are usually used
where a large wheel isn't feasible. When the water strikes the
blades (designed specially to reduce drag), it changes velocity.
This leads to a change in momentum, exerting a force on the
turbine blades. These turbines rely on the ability to take
all kinetic energy from the water to have high efficiencies.
Unlike reaction turbines, impulse turbines do not need to be
submerged. Types of impulse turbines include Pelton
turbines, Turgo turbines, and Crossflow turbines.
Reaction Turbine
In reaction turbines, the pressure of the water changes as it
moves through the blades of the turbine. Unlike in an impulse
turbine, the reaction turbine directly uses water pressure to
move blades instead of relying on a conversion of water
pressure to kinetic energy. This means that reaction turbines
need to be submersed in water. Additionally, components of
these turbines must be able to handle high pressure levels
inside the turbine. Here, the fluid velocity and reduction in
water pressure causes a reaction on the turbine blades, moving
them. Types of reaction turbines include Kaplan
turbines and Francis turbines.