• Oil reservoirs If the reservoir temperature, T, is less than the critical temperature, Tc, of the reservoir fluid, the reservoir is classified as an oil reservoir.
• Gas reservoirs If the reservoir temperature is
greater than the critical temperature of the
hydrocarbon fluid, the reservoir is considered a
gas reservoir.
RESERVOIR
---200-300BC ---10 to 15 m
--- elimNting descripencies ---Rock dams
Water availability, determination of storage capacity, operation of reservoir
Water is essential for human civilisation, living organisms,
and natural habitat. It has supernumeary applications in both domestic and industrial purposes .
Due to its multiple benefits and the problems created by its excesses, shortages and quality deterioration, water as a resource requires special attention.
How much do we have?
Global Water
•About 70% of the earth is covered in water.
•The total amount of water in the world is
approximately 1.4 billion km
3, of which 97.5% is saltwater and 2.5% is fresh water.
•Of the 35 million km
3of freshwater on earth, about 24.4 million km
3are locked up in the form of glacial ice, permafrost, or permanent snow. Groundwater and soil moisture account for 10.7 million km
3. Freshwater lakes and marshlands hold about 0.1 million km
3.
Rivers, the most visible form of fresh water account for
0.002 million km
3or about less than 0.01% of all forms
of fresh water.
WHERE IN THE WORLD IS MOST OF THE WATER?
IN THE OCEAN
WHERE IN THE WORLD IS MOST OF THE FRESHWATER?
FLOATING FROZEN IN THE OCEAN AS ICEBERGS AND GLACIERS
HOW MUCH WATER IS AVAILABLE FRESHWATER (WATER
WE CAN ACTUALLY GET TO)?
AVAILABLE WATER IS NOT EVENLY DISTRIBUTED
AROUND THE PLANET AND NEITHER ARE THE PEOPLE.
Average Annual Rainfall - 1170 mm
Maximum Average Annual Rainfall - 11000 mm
(Cherrapunji)
Minimum Average Annual Rainfall - 100 mm
(Western Rajasthan)
Sources of Irrigation
2.89 (5%)
2.53 (5%)
11.55 (21%)
15.98 (29%) 21.72 (40%)
Canals Tanks Tube Wells
Other Wells Other Sources
39%
13%
48%
Major & Medium Irrigation Minor (Surface Water)
Minor(Ground Water)
PARTICULARS QUANTITY
Geographical Area Flood Prone Area
Ultimate Irrigation Potential Total Cultivable Land Area Net Irrigated Area
Natural Runoff (Surface Water and Ground Water)
Estimated Utilisable Surface Water Potential
Groundwater Resource.
Available Groundwater resource for Irrigation
Net Utilisable Groundwater esource for irrigation
329 million ha.
40 million ha.
140 million ha.
184 million ha. . 50 million ha.
1869 Cubic km.
690 Cubic km.
432 Cubic km 361 Cubic km.
325 Cubic km.
Total Anticipated Demand
(In Billion cubic metre)
In 2010 :813 710 * In 2025 :1093 843 * In 2050 :1447 1180 * Total Utilisable Water :1122 (690+432)
S.W G.W
*
With improved management(In Billion cubic metre)
Total Precipitation : 4000 Total Water Availability :
1869
Total Utilisable Water :
1122
Surface Water - 690
Ground Water - 432
0 1000 2000 3000 4000 5000 6000
1951 1991 2001 2025 2050 Water Availibilty (Cubic meter per capita per year)
Water Stress Line
Water Scarcity Line
Efficiency of utilisation in all the diverse uses of water should be optimised and an awareness of water as a scarce resource should be fostered.
Conservation consciousness should be promoted through education, regulation, incentives and disincentives.
The resources should be conserved and the availability
augmented by maximising retention, eliminating
pollution and minimising losses. For this, measures
like lining in the conveyance system, modernization and
rehabilitation of existing systems , recycling and re-use
of treated effluents and techniques like drip and
sprinkler may be promoted .
“nature has enough for our need, but not for our greed”.
Pure water is the world’s first and foremost medicine.
Save- water Don’t waste the world’s blood .
Waste water today –live In desert tomorrow.
You are 60% water .save 60% of YOURLIFE.
A water supply scheme drawing water
directly from a river or a stream may fail to
satisfy the consumers demands during
extremely low flows , while during high flows
it may become difficult to carry out its
operation due to devastating floods , a barrier
in the form of dam is , therefore , constructed
across the river, so as to form a pool of water
on the upstream side of the dam is known as
a reservoirs.
Storage / conservation reservoir
Flood control reservoir
Multipurpose reservoir
Distribution reservoir
“A storage or a conservation reservoir
can retain such excess supplies during
periods of peak flows,and can release
them gradually during low flows as
and when the need arises.”
City water supply
Irrigationwater supply
Hydroelectric project
It may fail to satisfy the consumers demands during:
1). Extremely low flows 2). High flow
It may become difficult to carry out their
operations due to devastating floods.
CONTROLLING FLOOD
REDUCE FLOOD DAMAGE BELOW THE
RESERVOIR
“A flood control reservoir , generally called
a flood-mitigation reservoir , stores a
portions of the flood flows in such a way as
to minimise the flood peaks at the areas to
be protected downstream.”
The entire inflow entering the reservoir is discharged till the out flow reaches the safe capacity of the channel downstream.
The inflow in excess of this rate is stored in the reservoir , which is then gradually
released , so as to recover the storage capacity for the next flood.
A flood control reservoir differs from a
conservation reservoir only in its need for a large sluiceway capacity to permit rapid
drawdown before or after a flood.
There are two basic types of flood mitigation reservoirs;
(1). Storage reservoir;
(2). Retarding reservoir.
Storage reservoir:
‘A reservoir having gates and valves installation at its spillway and at its sluice outlets is known as storage reservoir.’
Retarding reservoir:
‘A reservoir with uncontrolled and ungated
outlets is known as a retarding basin or
retarding reservoirs.’
“ A reservoir planned and constructed
to serve not only one purpose but
various purpose together is called a
multipurpose reservoir.”
A multipurpose reservoir is a man-made lake which is managed for multiple purposes.
Multipurpose reservoirs may be managed to balance some or all of the following activities:
Water supply
Flood control
Soil erosion
Environmental management
Hydroelectric power generation
Navigation
Recreation
Irrigation
Bhakra Dam is a concrete gravity dam across the Sutlej River, and is near the border
between Punjab and Himachal Pradesh in northern India
A distribution reservoir connected with the
conduits of a primary water supply; used to
supply water to consumers according to
fluctuations in demand over short time
periods and serves for local storage in case
of emergency.
Such a reservoir can be filled by pumping water at a certain rate and can be used to supply water even at rate higher than inflow rate during period of maximum demands called critical periods of demand.
Such reservoirs are,therefore, helpful in
permitting the pumps or the water
treatment plants to work at a uniform rate,
and they store water during the hours of no
demand or less demand, and supply water
from their storage during the critical
periods of maximum demand…
The term “reservoir” can refer to a man-made or natural lake, as well as cisterns and subterranean reservoirs. In this section we focus only on man-made reservoirs.
Man-made reservoirs are made when dams are constructed across rivers, or by enclosing an area that is filled with water. There are two main types of man-made reservoirs: impoundment and off-stream (also called off-river).
Reservoirs can vary in size and be as small as a pond and as big as a large lake [1]. There is so much variability when it comes to
reservoirs – they can differ in size, shape and location. For this reason, it can be misleading to make blanket statements about reservoirs without “significant qualification as to their type” [2].
Depending on the purpose of a reservoir, operators will fill a
completed reservoir with water, let water flow on through the dam and downstream, or leave the reservoir site empty until it is needed (e.g. a dry dam site for flood mitigation).
Impoundment Reservoir
An impounding reservoir is a basin constructed in the valley of a stream or river for the purpose of holding stream flow so that the stored water may be used when supply is insufficient.
Off-Stream Reservoirs or distribution reservoir
Off-stream reservoirs are reservoirs that are not on a river course. Rather, off-stream reservoirs are formed by partially or completely enclosed waterproof banks.
The embankments around an off-stream reservoir are usually made from concrete or clay. The size of an off-river reservoir will depend on how large of an area is excavated and how high the embankment is built.
The basin constructed to equalize the supply and demand of the community or used for treated water and to provide supplies in emergency, is known as distribution reservoir.
The main difference between these two is
that the impounding reservoirs hold
untreated water white distribution holds
treated water. The water held by an
impounding reservoir may not all used as
treated water but may be used for other
purposes such as irrigation.
An environmental impact assessment (EIA) must be completed prior to construction beginning on a large or impactful reservoir and dam site. The EIA process is regulated at the federal government level by the Canadian Environmental Assessment Agency.
The Alberta government also has its own process for
completing an EIA. Alberta Environment and Sustainable
Resource Development is responsible for the laws that are
related to EIAs in Alberta (the Environmental Protection
and Enhancement Act and the Water Act). At an inter-
governmental level, the Canada-Alberta Agreement on
Environmental Assessment Cooperation is an agreement
between the federal government and the government of
Alberta that streamlines the EIA process and ensures that
the EIA meets the requirements set out by both levels of
government
PLANNING OF
RESERVOIR
Surface topography :
The site should provide a large area for storage of the water. Also, there should be suitable routes available for pipelines.
Sub-surface geology:
The site must provide :
Safe foundation for dam structure.
Water tightness against seepage.
Availability of local construction material.
Land for storage :
The land should be cheap and there should be less population.
Absence of objectionable soluble materials :
There should not be any soluble material present at site which cause change in odour, taste and color of water. As it may be harmful for people.
Availability of local construction material :
The construction material such as stones, binding material etc. should be locally available. So that the cost of the project may be reduced.
The first step in planning the construction of a
reservoir with the help of a dam is for the decision
makers to be sure of the needs and purposes for
which the reservoir is going to be built together with
the known constraints (including financial), desired
benefits. There may be social constraints, for
examples people’s activism may not allow a reservoir
to be built up to the desired level or even the
submergence of good agricultural level may be a
constraint. Some times, the construction of a dam may
be done that is labor intensive and using local
materials, which helps the community for whom the
dam is being built. This sort of work is quite common
in the minor irrigation departments of various steps,
especially in the drought prone areas. The Food-for-
Work schemes can be utilized in creating small
reservoirs that helps to serve the community.
The second step is the assembly of all relevant existing information, which includes the following:
Reports of any previous investigations and studies, if any.
Reports on projects similar to that proposed which have already been constructed in the region.
A geographical information system (GIS) for the area of interest may be created using a base survey map of the region.
Topographical data in the form of maps and satellite pictures, which may be integrated within the GIS.
Geological data in the form of maps and borehole logs, along with the values of relevant parameters.
Meteorological and hydrological data - of available parameters like rainfall, atmospheric and water temperatures, evaporation, humidity, wind speed, hours of sunshine, river flows, river levels, sediment concentration in rivers, etc.
For water supply projects, data on population and future population growth based on some acceptable forecast method, industrial water requirement and probable future industrial development.
For irrigation projects, data on soils in the project area and on the crops already grown, including water requirement for the crops.
For hydropower projects, data on past demand and forecasts of future public and industrial demand for power and energy;
data on existing transmission systems, including transmission voltage and capacity.
Data on flora and fauna in the project and on the fish in the rivers and lakes, including data on their migratory and breeding habits.
Data on tourism and recreational use of rivers and lakes and how this may be encouraged on completion of the proposed reservoir.
• Seismic activity data of the region that includes recorded peak accelerations or ground motion record.
The most important function is that water
should be available at all times. It does not
mean that largest reservoir must be
constructed. Size of reservoirs must be
adequate. It must not be too large and it
must not be too small. For this purpose, the
rate of water consumption of the community
or users should be known. In case of
impounding reservoir, the stream flow during
drought conditions should be calculated.
An environmental impact assessment (EIA) must be completed prior to construction beginning on a large or impactful reservoir and dam site. The EIA process is regulated at the federal government level. An EIA may include, but is not necessarily limited to, an analysis of the following:
Whether the safety of navigation is impacted by the proposed structure;
The impact of the structure on migratory fish; and
The impact of the structure on endangered riparian species or
fragile ecosystems.
Before construction can begin, the river must be diverted in order to make the building process easier. Water can be diverted through constructed channels on the surface alongside the river or through underground tunnels through the rock alongside the river. Both of these methods allow the water to travel downstream of the reservoir site and minimize the amount of water travelling to the construction zone.
A temporary dam called a cofferdam is built
above the main site of the permanent dam. The
cofferdam is intended to protect the construction
site in the event of a flood.
Once the dam structure is in place, the reservoir is almost ready to be filled. The land that will be underwater is first surveyed for anything that could potentially contaminate the water. Trash and debris are removed. Then, information signs will be placed around the reservoir and roads leading to the construction area will be barricaded. The reservoir can then be filled.
For on-stream storage, water will have already begun collecting behind the dam. However, for off-stream storage, water must be diverted to the reservoir.
During the filling process the reservoir site is
carefully monitored. Operators will watch for seepage
of water through the dam and stay alert for
mudslides or landslides, which can occur when the
soil and new embankment areas around the filling
reservoir are inundated and become wetter than
normal.
Water quality is monitored at the inflow and outflow of the reservoir and the reservoir water itself. Water quality can be affected by the reservoir since the water that was formerly flowing is now still. Over time, nutrients in the water can build-up and result in the growth of algae blooms (in Alberta, where most reservoirs are located closer to the mountains and inflows often have lower nutrient loads, algae bloom growth is less of a problem than it is in other jurisdictions).
Chemicals can also become concentrated in the
reservoir, making the water unsuitable for
drinking. In Alberta, there are regulations for
water quality in a reservoir. The Canadian
Fisheries Act regulates the harmful alteration of
fish habitat and any required compensation
A dam is a hydraulic structure or assembly that
is constructed across a river to form a
reservoir on its upstream side for confining
water for various purposes like Hydropower,
water supply, flood control, navigation,
fishing and recreation, irrigation. Dams are
constructed depending on the purpose for
which they are used. Different types of dams
are used for one or more of the above
purposes.
Nagarjunasagar Dam
Grand coulee, USA
Aswan high rock-fill dam located between Egypt and Sudan
An earth dam (made up of soil) is built by compacting each layers of soil. The most impervious material is used to form the core and placing the permeable material on the upstream and downstream sides. The side facing made of crushed stone prevents soil erosion. And the spillway made of concrete, protects the dam if the water overtops the dam.
This type of dam resists the forces exerted on it mainly because of the shear strength of the soil.
New Cornelia mine tailings, USA
Idukki Dam
Hoover dam, USA
Bartlett dam, USA
Crib dam
These specific levels and parts are generally defined as follows:
Full Reservoir Level (FRL): It is the level corresponding to the storage which includes both inactive and active storages and also the flood storage, if provided for. In fact, this is the highest reservoir level that can be maintained without spillway discharge or without passing water downstream through sluice ways.
Minimum Drawdown Level (MDDL): It is the level below which the reservoir will not be drawn down so as to maintain a minimum head required in power projects.
Dead Storage Level (DSL): Below the level, there are no outlets to drain the water in the reservoir by gravity.
Maximum Water Level (MWL): This id the water level that is ever likely to be attained during the passage of the design flood. It depends upon the specified initial reservoir level and the spillway gate operation rule. This level is also called sometimes as the Highest Reservoir Level or the Highest Flood Level.
RESERVOIR STORAGE ZONE AND USES OF RESERVOIR
Live storage : This is the storage available for the intended purpose between Full Supply Level and the Invert Level of the lowest discharge outlet. The Full Supply Level is normally that level above which over spill to waste would take place. The minimum operating level must be sufficiently above the lowest discharge outlet to avoid vortex formation and air entrainment.
This may also be termed as the volume of water actually available at any time between the Dead Storage Level and the lower of the actual water level and Full Reservoir Level.
Dead storage: It is the total storage below the invert level of the lowest discharge outlet from the reservoir. It may be available to contain sedimentation, provided the sediment does not adversely affect the lowest discharge.
Outlet Surcharge or Flood storage: This is required as a reserve between Full Reservoir Level and the Maximum Water level to contain the peaks of floods that might occur when there is insufficient storage capacity for them below Full Reservoir Level.
RESERVOIR STORAGE ZONE AND USES OF RESERVOIR
Some other terms related to reservoirs are defined as follows:
Buffer Storage : This is the space located just above the Dead Storage Level up to Minimum Drawdown Level. As the name implies, this zone is a buffer between the active and dead storage zones and releases from this zone are made in dry situations to cater for essential requirements only. Dead Storage and Buffer Storage together is called Interactive Storage.
Within-the-Year Storage: This term is used to denote the storage of a reservoir meant for meeting the demands of a specific hydrologic year used for planning the project.
Carry-Over Storage: When the entire water stored in a reservoir is not used up in a year, the unused water is stored as carry-over storage for use in subsequent years.
Silt / Sedimentation zones: The space occupied by the sediment in the reservoir can be divided into separate zones. A schematic diagram showing these zones is illustrated in Figure 2 .
RESERVOIR STORAGE ZONE AND USES OF RESERVOIR
Freeboard : It is the margin kept for safety between the level at which the dam would be overtopped and the maximum still water level.
This is required to allow for settlement of the
dam, for wave run up above still water level and
for unforeseen rises in water level, because of
surges resulting from landslides into the reservoir
from the peripheral hills, earthquakes or
unforeseen floods or operational deficiencies.
In general, the performance assessment of reservoir
projects has to be done for varying hydrologic inputs
to meet varying demands. Although analytical
probability based methods are available to some
extent, simulation of the reservoir system is the
standard method. The method is also known as the
working tables or sequential outing. In this method,
the water balance of the reservoir s and of other
specific locations of water use and constraints in the
systems are considered. All inflows to and outflows
from the reservoirs are worked out to decide the
changed storage during the period. In simulation
studies, the inflows to be used may be either
historical inflow series, adjusted for future up stream
water use changes or an adjusted synthetically
generated series.
Though a dam is constructed to build a reservoir,
a reservoir has a large area of spread and
contained in a big chunk of the river valley
upstream of the dam. Hence, while identifying a
suitable site for a proposed dam, it is of
paramount importance that the proposed
reservoir site is also thoroughly investigated and
explored. The basis of planning for such
explorations is to have a rapid economical and
dependable pre-investment evaluation of
subsurface conditions. It is also necessary that a
degree of uniformity be followed while carrying
out subsurface explorations so that the frame of
reference of the investigation covers all requisite
aspects.
Since reservoir projects in river valleys are meant to hold water; therefore, the following aspects of the reservoirs have to be properly investigated.
(a) Water tightness of the basins (b) Stability of the reservoir rim
(c) Availability of construction material in the reservoir area
(d) Silting
(e) Direct and indirect submergence of economic mineral wealth
(f) Seismo-techtonics
Loss of reservoir water would mainly take place due
to evaporation and a number of methods have been
suggest for controlling such loss. As such,
percolation or seepage loss is small for most of the
reservoirs and progressively gets lowered with the
passage of time since the sediment getting deposited
at the reservoir bottom helps to reduce percolation
losses. Of course, in some hills and valleys forming
the reservoir, there may be continuous seams of
porous rock strata or limestone caverns which cause
huge amount of water to get drained out of the
reservoirs.
A number of factors affect the evaporation from open water surface, of which, the major factors are water spread area and frequent change of speed and
direction of wind over the water body. Other meteorological factors like.
a) Vapour pressure difference_ between water surface and the layer of air above;
b) Temperature of water and air;
c) Atmospheric pressure;
d) Radiation;
e) Heat storage in water body; and f) Quality of water,
have direct influence on the rate of evaporation.
Since the meteorological factors affecting evaporation cannot be controlled under normal conditions, efforts are made for inhibition of evaporation by control of flow of wind over water surface or by protection of the water surface area by physical or chemical
methods. The methods generally used are as follows:
a) Wind breakers,
b) Covering the water surface,
c) Reduction of exposed water surface, d) Integrated operation of reservoirs, and
e) Treatment with chemical water evaporetardants
(WERs).
Wind is one of the most important factors which affect rate of evaporation loss from water surface. The greater the movement of air over the water surface, greater is the evaporation loss. Planting of trees normal to windward direction is found to be an effective measure for checking of evaporation loss. Plants (trees, shrubs or grass) should be grown around the rim of tanks in a row or rows to act as wind breaker. These wind breakers are found to influence the temperature, atmospheric humidity, soil moisture, evaporation and transpiration of the area protected.
Plants to act as wind breakers are usually arranged in
rows, with tallest plants in the middle and the smallest
along the end rows, so that more or less conical
formation is formed.
Covering the surface of water bodies with fixed or floating covers considerably retards evaporation loss.
These covers reflect energy inputs from atmosphere, as a result of which evaporation loss is reduced. The covers literally trap the air and prevent transfer of water vapour to outer atmosphere.
Fixed covers are suitable only for relatively small
storages. For large storages, floating covers or mat or
spheres may be useful and effective. However, for large
water surfaces the cost of covering the surface with
floats is prohibitive, Further in case of reservoirs with
flood outlets, there is also the danger of floats being
lost over spillway or through outlets. The floating
covers are thus of limited utility to larger water bodies.
In this method shallow portions of the reservoirs
are isolated or curtailed by construction of
dykes or bunds at suitable locations. Water
accumulated during the monsoon season in
such shallow portions is diverted or pumped to
appropriate deeper pockets in summer months,
so that the shallow water surface area exposed
to evaporation is effectively reduced.
You must first compare your pond water requirements - the water needed to initially fill your pond and to compensate for seepage and evaporation losses - with the water available from your source.
If you find that your water source provides enough water to fill the pond in a reasonable period of time, to fill it when you want to fill it, and to compensate for water losses throughout the year, you will not need a reservoir.
If you find that your water source does not provide enough
water to fill the pond and to compensate for water losses at
certain times of the year, but there is enough water available
over the year, you may decide to build a reservoir and store
the water you will need.
Your source provides a supply of water
throughout the year: If your daily water flow
is great enough throughout the year to
compensate for water losses by seepage and
evaporation, but not great enough to fill the
pond in a reasonable period of time, and to
fill it when you want to fill it, you will only
need a reservoir with a volume equal to the
pond volume, or even less, since the reservoir
is being supplied constantly.
Your source dries up completely and provides no water at certain times of the year.
If your source does not supply water throughout the year, but dries up at certain times, you should plan to fill your pond during the year either from a reservoir, or directly from the source at a time when there is enough water available.
If you are able initially to fill your pond at a time when water is available, your reservoir need only contain enough water to compensate for water losses by seepage and evaporation during the dry season.
If you are unable initially to fill your pond at a time when there
is water available, you may need to build a larger reservoir to
store water over a longer period of time, and that will contain
enough water to fill the pond and to compensate for water
losses.
A reservoir is subject to water losses by seepage and evaporation just as a pond is. To offset water losses from a reservoir, plan the water volume of the reservoir 1.5 times greater than the water volume you require to satisfy total water requirements.
VOLUME OF RESERVOIR=
1.5 x TOTAL WATER REQUIREMENTS FOR
PONDS
If you are going to build a reservoir, look for a site that will allow you to retain the greatest volume of water with the smallest dam possible. Dams require a great deal of work to build and to maintain, and the smaller the dam, the better.
Avoid a site in a valley, relatively open and
wide at the downstream end. At such a site
you will have to build a large dam.
