Explain about Estimation of Water
Demand ?
While estimating the water
demand, the above factors should be considered e.g. the size of the city; its
population does matter when estimating the water demand. The more the size of
population, more will be the demand. Estimation of water demand is necessary
to:
§ Calculate
design flow
§ Determine
the pumping power of machines to be used
§ Reservoir
capacity
§ Pipe
capacity
To
estimate water demand, following parameters must be determined or calculated.
1. Average
daily water consumption: It is based on complete one year supply of
water. It is the total consumption during one year, divided by the
population. q = (Q / P x 365) lpcd (liters per capita per day)
2. Maximum
daily consumption: It is the maximum amount of water used during
one day in the year. This amount is 180% of the average daily consumption
MDC = 1.8 x Avg. daily consumption. It is usually a working
day (Monday) of summer season.
3. Maximum
weekly demand: The amount of water used by a population
during awhole single weekin a study span of 1 year.
Maximum weekly demand = 1.48 x Avg. D. C
Maximum monthly demand = 1.28 x Avg. D. C
Maximum hourly demand = 1.5 x Avg. D. C
Maximum daily demand =
1.8 x Avg. D. C
4. Fire water demand | Fire Demand: Theamount of water usedfor fire fighting is termed as fire demand. Although, the amount of water used in fire fighting is a negligible part of the combine uses of water but the rate of flow and the volume required may be so high during fire that it is a deciding factor for pumps, reservoirs and distribution mains. Minimum fireflow should be 500gpm (1890L/m) Minimum fire flow should be 8000 gpm (32, 400 L/m) Additional flow may be required to protect adjacent buildings.
Sources of Fresh water Documentary Video on Concrete
Flowchart of the sources of clean drinking water
Waste Water
Treatment Disposal & Management
The
quantity of water required for a community depends upon:
1. Forecasted
population
2. Types and
variation in demand (e.g. seasonal variation)
3. Maximum
demand (Per day/Per month)
4. Fire
demand
5. Rural
demand and supplies
6. Appropriate
/ Available technology
Main
sources of water are
§ Surface
water sources: Lakes impounding reservoirs, streams, seas,
irrigation canals
§ Ground
water sources: Springs, wells, infiltration wells
Above are
the common sources of clean drinking water, other different sources of drinking
water are
Merits of
surface sources
Merits of
ground water sources
1. Being
underground, the ground water supply has less chance of being contaminated by
atmospheric pollution.
2. The water
quality is good and better than surface source.
3. Prevention
of water through evaporation is ensured and thus loss of water is reduced.
4. Ground
water supply is available and can even be maintained in deserted areas.
5. The land
above ground water source can be used for other purposes and has less
environmental impacts.
Demerits
of ground water source
1. The water
obtained from ground water source is always pressure less. A mump is required
to take the water out and is then again pumped for daily use.
2. The
transport / transmission of ground water is a problem and an expensive work.
The water has to be surfaced or underground conduits are required.
3. Boring
and excavation for finding and using ground water is expensive work.
4. The
modeling, analysis and calculation of ground water is less reliable and based
on the past experience, thus posing high risk of uncertainty.
Demerits
of surface source
Chemical
Characteristics of water
§ Acidity
§ Alkalinity
§ Hardness
§ Turbidity
Acidity:
Acidity or alkalinity is measured
by pH. PH measures the concentration
of Hydrogen ions in water.
Ionization of water is
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HOH H+ + OH-
In neutral solutions [OH] = [H]
hence pH = 7
If acidity is increased, [H] increases and pH reduces from 7
(because H is log of [H]). The value of pH of water is important in the
operations of many water and waste water treatment processes and in the control
of corrosion.
Alkalinity:
The values of pH higher than 7,
shows alkalinity. The alkaline species in water can neutralize acids. The major
constituents of alkalinity (or causticity) are OH-, CO32- and bicarbonates HCO3
ions. Alkalinity in water is usually caused by bicarbonate ions.
Hardness of water: Definition of
hard water
Hardness is the property that makes water to require more soap
to produce a foam or lather. Hardness of water is not harmful for human
health but can be precipitated by heating so can produce damaging
effects in boilers, hot pipes etc by depositing the material and reducing the
water storage and carriage capacity.
Absolute soft water on the
other hand is not acceptable for humans because it may cause ailments,
especially to heart patients. Hardness in water is commonly classified in terms
of the amount of CaCO3 (Calcium Carbonate) in it.
Concentration of CaCO3 Degree of hardness
0 - 75 mg / L Soft
75 - 150 mg / L Moderately
hard
150 - 300 mg / L Hard
300 up mg / L Very
Hard
Low level of hardness
can be removed just by boiling but high degree of hardness can be This method
has also the benefit that iron and manganese .removed by addition of lime
.organisms are reduced-including
micro contents are removed and suspended particles
Reservoir
A reservoir (etymology from French réservoir a
"storehouse ) or an artificial lake is used to store water.
Reservoirs may be created in river valleys by the construction of a dam or may
be built by excavation in the ground or by conventional construction techniques
such as brickwork or cast concrete.
The term reservoir may also be used to describe underground
reservoirs such as an oil or water well.
A dam is any barrier that holds back water; dams are primarily
used to save, manage, and/or prevent the flow of excess water into specific
regions. In addition, some dams are used to generate hydropower. This article
examines man-made dams but dams can also be created by natural causes like mass
wasting events or even animals like the beaver.
Another term often used when discussing dams is reservoir. A
reservoir is a man-made lake that is primarily used for storing water. They can
also be defined as the specific bodies of
water formed by the construction
of a dam. For example, the Hetch Hetchy Reservoir in
California's Yosemite National Park is the body of
water created and held back by the O'Shaughnessy Dam.
Types of Dams
Today, there are several
different types of dams and the man-made ones are classified by their size and
structure. Typically a large dam is classified as being higher than 50-65 feet
(15-20 meters) while major dams are those over 492-820 feet (150-250 meters).
One of the most common types of
major dams is the arch dam. These masonry or concrete dams are ideal for narrow
and/or rocky locations because their curved shape easily holds back water via
gravity without the need for a lot of construction materials. Arch dams can
have one large single arch or they can have multiple small arches separated by
concrete buttresses. The Hoover Dam which is on the border of the U.S.
stateAnother type of dam is the buttress dam. These can have multiple arches,
but unlike a traditional arch dam, they can be flat as well. Normally buttress
dams are made of concrete and feature a series braces called buttresses along
the downstream side of the dam to prevent the natural flow of water. The
Daniel-Johnson Dam in Quebec, Canada is a multiple arch buttress dam.
In the U.S., the most common type
of dam is the embankment dam. These are large dams made out of soil and rock
which use their weight to hold back water. To prevent water from
moving through them, embankment
dams also have a thick waterproof core. The Tarbela Dam in
Pakistan is the world's largest embankment dam.
Finally, gravity dams are huge
dams that are constructed to hold back water using only their own weight. To do
this, they are constructed using extensive amounts of concrete, making them
difficult and expensive to build. The Grand Coulee Dam in the U.S. state of
Washington is a gravity dam.
Types of Reservoirs and
Construction
Like dams, there are different
types of reservoirs as well but they are classified based on their use. The
three types are called: a valley dammed reservoir, a bank-side reservoir, and a
service reservoir. Bank-side reservoirs are those formed when water is taken
from an existing stream or river and stored in a nearby reservoir. Service
reservoirs are mainly constructed to store water for later use. They often
appear as water towers and other elevated structures.
The first
and usually largest type of reservoir is called a valley dammed reservoir.
These are
reservoirs that are located in
narrow valley areas where tremendous amounts of water can be held
in by the valley's sides and a dam. The best location for a dam in these types
of
reservoirs is where it can be
built into the valley wall most effectively to form a water tight seal.
To construct a valley dammed
reservoir, the river must be diverted, usually through a tunnel, at the start
of work. The first step in creating this type of reservoir is the pouring of a
strong foundation for the dam, after which construction on the dam itself can
begin. These steps can take months to years to complete, depending on the size
and complexity of the project. Once finished, the diversion is removed and the
river is able to flow freely toward the dam until it gradually fills the
reservoir.
Dam
Controversy
In addition to the high cost of
construction and river diversion, dams and reservoirs are often controversial
projects because of their social and environmental impacts. Dams themselves
affect many different ecological components of rivers such as fish migrations,
erosion, changes in water temperature and therefore changes in oxygen levels,
creating inhospitable environments for many species.
In addition,
the creation of a reservoir requires the flooding of large areas of land, at
the
expense of the natural
environment and sometimes villages, towns and small cities. The construction
of China's Three Gorges Dam, for example, required the relocation of over
one
million
people and flooded many different archaeological and cultural sites.
Main Uses
of Dams and Reservoirs
Despite their controversy, dams
and reservoirs serve a number of different functions but one of the largest is
to maintain an area's water supply. Many of the world's
largest urban areas
are supplied with water from
rivers that are blocked via dams. San Francisco, California for example, gets
the majority of its water supply from the Hetch Hetchy Reservoir via the Hetch
Hetchy Aqueduct running from Yosemite to the San Francisco Bay Area.
Another major use of
dams is power generation as hydroelectric power is one of the world's major
sources of electricity. Hydropower is generated when the potential energy of
the water
on the dam drives a water turbine
which in then turns a generator and creates electricity. To best
make use of the water's power, a common type of hydroelectric dam uses
reservoirs with
different levels to adjust the
amount of energy generated as it is needed. When demand is low for instance,
water is held in an upper reservoir and as demand increases, the water is
released into a lower reservoir where it spins a turbine.
Some other important uses of dams
and reservoirs include a stabilization of water flow and irrigation, flood
prevention, water diversion and recreation.
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