An Overview of Reservoir Types and Purposes
RESERVOIR
Content…
Types,
Investigations,
Site
selection,
Zones
of
storage,
Safe
yield,
Reservoir
capacity,
Reservoir
sedimentation
and
control.
What is a
Reservoir?
It
is
a
n
are
a
d
e
v
e
l
o
p
ed
b
y
wat
e
r
bod
y
du
e
to
construction of
dam.
Tarbela
Dam
JungHua Dam
(Taiwan)
Storage
reservoir serve
the
following
purpose
:
Irrigation
Water
supply
Hydroelectric
power
generation
Flood
control
Navigation
Recreation
Development
of fish & wild
life
Soil
conservation
Classification
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Investigations
Engineering
surveys
Geological
investigations
Hydrological
investigations
Engineering
surveys
Conducted for
dam,
reservoir
and
other
associated
work.
Topographic
survey of the
area
is
carried
out and the contour
plan is
prepared
The
horizontal control
is usually
provided
by
triangulation
survey,
and the
vertical
control
by precise
levelling.
Geological
investigation
Geological investigations
of
the dam and
reservoir site are
done for the following
purposes.
(i)
Suitability
of
foundation for the
dam.
(ii)
Watertightness
of the reservoir
basin
(iii)
Location
of the
quarry
sites for
the
construction
materials.
Hydrological
investigations
The
hydrological investigations are
conducted for the following
purposes
:
(i)
To study the
runoff pattern and
storage
capacity.
(ii)
To
determine
the maximum
discharge
at the
site.
Site
selection
Large storage
capacity
River valley should be narrow,
length
of
dam
to constructed
is
less.
Watertightness of
reservoir.
Good
hydrological
conditions
Deep
reservoir
Small
submerged
area
Low silt
inflow
No objectionable
minerals
Low
cost of
real
estate
Site easily
accessible
Zones of
storage
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p
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c
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i
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e
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s
i
g
n
f
l
o
o
d
.
Safe
yield
Yield
is the volume of
water
which can
be
withdrawn
from a reservoir in a
specified
period
of
time.
Safe
yield is
the maximum quantity
of
water
which can be
supplied from
a
reservoir in a
specified period
of
time
during
a critical
dry
year.
S
e
c
o
n
d
a
r
y
y
i
e
l
d
:
i
s
t
h
e
q
u
a
n
t
i
t
y
o
f
w
a
t
e
r
w
h
i
c
h
i
s
a
v
a
i
l
a
b
l
e
d
u
r
i
n
g
t
h
e
p
e
r
i
o
d
o
f
h
i
g
h
f
l
o
w
i
n
t
h
e
r
i
v
e
r
s
w
h
e
n
t
h
e
y
i
e
l
d
i
s
m
o
r
e
t
h
a
n
t
h
e
s
a
f
e
y
i
e
l
d
.
a
r
it
h
met
i
c
averag
e
o
f
the
fi
r
m
y
i
e
l
d
and
A
v
e
r
a
g
e
y
i
e
l
d
:
T
h
e
a
v
e
r
a
g
e
y
i
e
l
d
i
s
t
h
e
t
he
secondary
yield
over a
long
period of
time.
D
e
s
i
g
n
y
i
e
l
d
:
T
h
e
d
e
s
i
g
n
y
i
e
l
d
i
s
t
h
e
y
i
e
l
d
a
d
o
p
t
e
d
i
n
t
h
e
d
e
s
i
g
n
o
f
a
r
e
s
e
r
v
o
i
r
.
T
h
e
d
e
s
i
g
n
y
i
e
l
d
i
s
u
s
u
a
l
l
y
f
i
x
e
d
a
f
t
e
r
c
o
n
s
i
d
e
r
i
n
g
t
h
e
u
r
g
e
n
c
y
o
f
t
h
e
w
a
t
e
r
n
e
e
d
s
a
n
d
t
h
e
a
m
o
u
n
t
o
f
r
i
s
k
i
n
v
o
l
v
e
d
.
Reservoir
capacity
depends upon the inflow available
and
demand
inflow
in
the
river is always
greater
than
the
demand, there
is no
storage
required
if the
inflow
in the river is small
but the
demand
is
high,
a
large reservoir
capacity
is
required
The
required
capacity for a
reservoir
can
be
determined
by the
following
methods:
1.
Graphical
method,
using
mass
curves.
2.
Analytical
method
Graphical
method
1.
Prepare a mass inflow curve from the flow
hydrograph of the site for a number of
consecutive years including the most critical
years (or the
driest years)
when the
discharge is
low.
2.
Prepare the
mass
demand curve
corresponding
to the given
rate
of demand. If the rate of
demand is
constant,
the mass demand
curve is
a
straight
line. The scale of the
mass
demand
curve should be the same as
that
of the mass
inflow
curve.
3.
Draw the lines
AB,
FG,
etc.
such
that
(i)
They are
parallel
to
the
mass demand
curve,
and
(ii)
They are
tangential
to the
crests
A, F,
etc.
of
the mass
curve.
4.
Determine the
vertical intercepts
CD. HJ, etc.
between the
tangential lines and
the mass inflow
curve. These
intercepts
indicate the volumes by
which the inflow volumes fall
short
of
demand.
Assuming that the
reservoir is
full at
point
A, the
inflow volume
during
the
period
AE is equal to
ordinate DE and the demand is
equal to
ordinate
CE.
Thus the
storage required
is equal to the
volume
indicated by
the
intercept
CD.
5. Determine the
largest
of the vertical
intercepts
found in Step
(4).
The
largest vertical intercept
represents
the
storage capacity
required.
The following points should be
noted.
(i)
The
capacity obtained
in the net
storage
capacity which must be
available
to meet the
demand. The gross capacity of the
reservoir
will
be more
than the
net
storage capacity. It
is
obtained by adding the evaporation and
seepage losses
to
the
net
storage
capacity.
(ii)
The
tangential lines
AB, FG;
etc. when
extended
forward must
intersect
the curve. This
is
necessary
for the
reservoir to
become full
again,
If these
lines do
not intersect
the mass
curve, the
reservoir
will not be
filled again.
However,
very
large
reservoirs
sometimes do
not get refilled
every year.
In that
case,
they may
become
full
after
2-3
years.
(iii)
The
vertical
distance such as FL between
the
successive tangents represents the
volume
of water spilled
over
the spillway of the
dam.
Analytical
method
•
capacity of the reservoir is
determined
from
the net inflow and
demand.
•
storage
is
required
when
the
demand
exceeds the
net
inflow.
•
the total storage required
is
equal to
the
sum of the
storage required during the
various
periods.
1.
Collect the stream
flow
data at the
reservoir
site
during
the
critical
dry
period. Generally, the
monthly inflow
rates
are
required.
However, for
very large
reservoirs,
the annual inflow rates
may be
used.
2.
Ascertain the
discharge
to be
released
downstream to satisfy water rights or to honour
the agreement between the
states
or the
cities.
3.
Determine the direct
precipitation volume
falling on the
reservoir during
the
month.
4.
Estimate the
evaporation
losses which would
occur
from
the reservoir
„The
panevaporation
data
are normally
used
for the
estimation
of
evaporation losses during the month.
5.
Ascertain the demand
during various
months.
6.
Determine the
adjusted
inflow
during different
months as
follows:
Adjusted inflow = Stream inflow +
Precipitation
-
Evaporation – Downstream
Discharge
7.
Compute the
storage
capacity for
each
months.
Storage
required
= Adjusted inflow –
Demand
8.
Determine the total
storage capacity
of the
reservoir
by adding the
storages required
found
in Step
7.
Determination of
Yield
of
a
Reservoir
The
yield from
a
reservoir
of a
given capacity
can be
determined
by the use of the
mass
inflow
curve
1.
Prepare the mass inflow curve from the
flow
hydrograph of the
river.
2.
Draw tangents
AB,
FG,
etc.
at the crests A, F,
etc.
of the
mass
inflow curve in
such
a way
that
the maximum
departure (intercept)
of these
tangents
from
the mass inflow curve is
equal
to
the given
reservoir
capacity.
3.
Measure
the
slopes of
all the
tangents
drawn
in Step
2.
4.
Determine the slope
of
the
flattest
tangent.
5.
Draw
the mass demand
curve from
the
slope of the
flattest tangent
(see insect).
The yield is
equal
to
the
slope of
this
line
Reservoir
Sedimentation
is a
difficult
problem for which an
economical
solution
has
not
yet been
discovered,
except by
providing a “dead storage” to accommodate the
deposits
during
the life of the
dam.
Disintegration,
erosion,
transportation,
and
sedimentation, are the
different
stages leading
to
silting of
reservoir.
Causes of
sedimentation
Nature of soil
in
catchment
area
Topography
of
the catchment
area
Cultivation
in catchment
area
Vegetation
cover in catchment
area
Intensity
of
rainfall
in
catchment
area
Sediment
Management
•
Maximum efforts should water should
be
released
so
that
less
sediments should
retain in
reservoir.
Following options
are:
–
Catchment
Vegetation
–
Cons
t
r
u
ction
o
f
coff
e
r
d
a
ms/l
o
w
h
e
ig
h
t
barriers
–
Flushing and desilting of
sediments
–
Low
level
outlets
/
sediment
sluicing
Catchment
vegetation
Catchment
vegetation
Wooden
barriers
Wooden
barriers
Stepped watershed for
sediment
control
Flushing of
sediments
from
reservoir
Mechanical desilting from
reservoir
Sediment
sluicing
Sediment
sluicing
Reservoirs play a crucial role in managing water resources for various purposes like irrigation, hydroelectric power generation, flood control, and more. This article explores different types of reservoirs such as storage, flood control, retarding, and detention reservoirs, along with their functions and classifications. From investigations to engineering surveys, learn about the essential aspects of reservoir planning and development.
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Presentation Transcript
Content Types, Investigations, Site selection, Zones of storage, Safe yield, Reservoir capacity, Reservoir sedimentation and control.
What is a Reservoir? It is an area developed by water body due to construction of dam. JungHua Dam (Taiwan) Tarbela Dam
Storage reservoir serve the following purpose : Irrigation Water supply Hydroelectric power generation Flood control Navigation Recreation Development of fish & wild life Soil conservation
Classification Storage Reservoirs: Storage reservoirs are also called conservation reservoirs because they are used to conserve water. Storage reservoirs are constructed to store the water in the rainy season and to release it later when the river flow is low Flood Control Reservoirs: A flood control reservoir is constructed for the purpose of flood control. It protects the areas lying on its downstream side from the damages due to flood.
Retarding Reservoirs: A retarding reservoir is provided with spillways and sluiceways which are ungated. The retarding reservoir stores a portion of the flood when the flood is rising and releases it later when the flood is receding. Detention Reservoirs : A detention reservoir stores excess water during floods and releases it after the flood. It is similar to a storage reservoir but is provided with large gated spillways and sluiceways to permit flexibility of operation.
Distribution Reservoirs: A distribution reservoir is a small storage reservoir to tide over the peak demand of water for municipal water supply or irrigation. The distribution reservoir is helpful in permitting the pumps to work at a uniform rate. It stores water during the period of lean demand and supplies the same during the period of high demand. Multipurpose Reservoirs: The are constructed for more than single purpose. Balancing Reservoirs: A balancing reservoir is a small reservoir constructed d/s of the main reservoir for holding water released from the
Investigations Engineering surveys Geological investigations Hydrological investigations
Engineering surveys Conducted for dam, reservoir and other associated work. Topographic survey of the area is carried out and the contour plan is prepared The horizontal control is usually provided by triangulation survey, and the vertical control by precise levelling.
Geological investigation Geological investigations of the dam and reservoir site are done for the following purposes. (i) Suitability of foundation for the dam. (ii) Watertightness of the reservoir basin (iii)Location of the quarry sites for the construction materials.
Hydrological investigations The hydrological investigations are conducted for the following purposes : (i)To study the runoff pattern and storage capacity. (ii)To determine the maximum discharge at the site.
Site selection Large storage capacity River valley should be narrow, length of dam to constructed is less. Watertightness of reservoir. Good hydrological conditions Deep reservoir
Small submerged area Low silt inflow No objectionable minerals Low cost of real estate Site easily accessible
Full reservoir level (FRL): The full reservoir level (FRL) is the highest water level to which the water surface will operating conditions. rise during normal Maximum water level (MWL): The maximum water level is the maximum level to which the water surface will rise when the design flood passes over the spillway. Minimum pool level: The minimum pool level is the lowest level up to which the water is withdrawn from the reservoir under ordinary conditions.
Dead storage: The volume of water held below the minimum pool level is called the dead storage. It is provided to cater for the sediment deposition by the impounding sediment laid in water. Normally it is equivalent to volume of sediment expected to be deposited in the reservoir during the design life reservoir. Live/useful storage: The volume of water stored between the full reservoir level (FRL) and the minimum pool level is called the useful storage. It assures the supply of water for specific period to meet the demand.
Bank storage: is developed in the voids of soil cover in the reservoir available as seepage of water when water levels drops down. It increases the reservoir capacity over and above that given by elevation storage curves. area and becomes Valley storage: The volume of water held by the natural river channel in its valley up to the top of its banks before the construction of a reservoir is called the valley storage. The valley storage depends upon the cross section of the river.
Flood/Surcharge storage: is storage contained between maximum reservoir level and full reservoir levels. It varies with spillway capacity of dam for given design flood.
Safe yield Yield is the volume of water which can be withdrawn from a reservoir in a specified period of time. Safe yield is the maximum quantity of water which can be supplied from a reservoir in a specified period of time during a critical dry year.
Secondary yield: is the quantity of water which is available during the period of high flow in the rivers when the yield is more than the safe yield. The average yield is the the Average yield: arithmetic average of the firm yield and secondary yield over a long period of time. Design yield: The design yield is the yield adopted in the design of a reservoir. The design yield is usually fixed after considering the urgency of the water needs and the amount of risk involved.
Reservoir capacity depends upon the inflow available and demand inflow in the river is always greater than the demand, there is no storage required if the inflow in the river is small but the demand is high, a large reservoir capacity is required
The required capacity for a reservoir can be determined by the following methods: 1. Graphical method, using mass curves. 2. Analytical method
Graphical method 1. Prepare a mass inflow curve from the flow hydrograph of the site for a number of consecutive years including the most critical years (or the driest years) when the discharge is low. 2. Prepare the mass demand curve corresponding to the given rate of demand. If the rate of demand is constant, the mass demand curve is a straight line. The scale of the mass demand curve should be the same as that of the mass inflow curve.
3. Draw the lines AB, FG, etc. such that (i)They are parallel to the mass demand curve, and (ii)They are tangential to the crests A, F, etc. of the mass curve. 4. Determine the vertical intercepts CD. HJ, etc. between the tangential lines and the mass inflow curve. These intercepts indicate the volumes by which the inflow volumes fall short of demand.
Assuming that the reservoir is full at point A, the inflow volume during the period AE is equal to ordinate DE and the demand is equal to ordinate CE. Thus the storage required is equal to the volume indicated by the intercept CD. 5. Determine the largest of the vertical intercepts found in Step (4). The largest vertical intercept represents the storage capacity required.
The following points should be noted. (i)The capacity obtained in the net storage capacity which must be available to meet the demand. The gross capacity of the reservoir will be more than the net storage capacity. It is obtained by adding the evaporation and seepage losses to the net storage capacity.
(ii)The tangential lines AB, FG; etc. when extended forward must intersect the curve. This is necessary for the reservoir to become full again, If these lines do not intersect the mass curve, the reservoir will not be filled again. However, very large reservoirs sometimes do not get refilled every year. In that case, they may become full after 2-3 years. (iii)The vertical distance such as FL between the successive tangents represents the volume of water spilled over the spillway of the dam.
Analytical method capacity of the reservoir is determined from the net inflow and demand. storage is required when the demand exceeds the net inflow. the total storage required is equal to the sum of the storage required during the various periods.
1.Collect the stream flow data at the reservoir site during the critical dry period. Generally, the monthly inflow rates are required. However, for very large reservoirs, the annual inflow rates may be used. 2.Ascertain the discharge to be released downstream to satisfy water rights or to honour the agreement between the states or the cities.
3.Determine the direct precipitation volume falling on the reservoir during the month. 4.Estimate the evaporation losses which would occur from the reservoir The panevaporation data are normally used for the estimation of evaporation losses during the month. 5. Ascertain the demand during various months.
6.Determine the adjusted inflow during different months as follows: Adjusted inflow = Stream inflow + Precipitation - Evaporation Downstream Discharge 7.Compute the storage capacity for each months. Storage required = Adjusted inflow Demand 8.Determine the total storage capacity of the reservoir by adding the storages required found in Step 7.
Determination of Yield of a Reservoir The yield from a reservoir of a given capacity can be determined by the use of the mass inflow curve 1.Prepare the mass inflow curve from the flow hydrograph of the river. 2.Draw tangents AB, FG, etc. at the crests A, F, etc. of the mass inflow curve in such a way that the maximum departure (intercept) of these tangents from the mass inflow curve is equal to the given reservoir capacity.
3.Measure the slopes of all the tangents drawn in Step 2. 4.Determine the slope of the flattest tangent. 5.Draw the mass demand curve from the slope of the flattest tangent (see insect). The yield is equal to the slope of this line
Reservoir Sedimentation is a difficult problem for which an economical solution has not yet been discovered, except by providing a dead storage to accommodate the deposits during the life of the dam. Disintegration, erosion, transportation, and sedimentation, are the different stages leading to silting of reservoir.
Causes of sedimentation Nature of soil in catchment area Topography of the catchment area Cultivation in catchment area Vegetation cover in catchment area Intensity of rainfall in catchment area
Sediment Management Maximum efforts should water should be released so that less sediments should retain in reservoir. Following options are: Catchment Vegetation Construction of coffer dams/low height barriers Flushing and desilting of sediments Low level outlets / sediment sluicing
Stepped watershed for sediment control
