This document provides an overview of the design process for a new diversion dam project on the Tarbela Dam in Pakistan. It discusses selecting the site, conducting site studies to understand the geology and foundation conditions, determining the appropriate dam type is an earth-fill dam, designing the embankment, investigating the reservoir area, conducting test fills, studying causes of dam failure, developing the flood hydrograph, and collecting basic hydrologic and meteorological data. The project will require detailed exploration of the foundation and subsurface conditions to support the earth-fill dam design and ensure the stability and safety of the new diversion dam.

1. Graduate School of Water Resources
Design of Diversion Dam in Tarbela Dam Pakistan
Designed by: Muhammad Shoaib
Student # : 2015730558

2. Introduction
Contents
1.Site Selection
2.Site Study
3.Dam Type selection
4.Embankment
5.Geology and foundation conditions
6.Reservoir investigations
7.Test fills
8.Study of causes of dam failure
9.Flood Hydrograph
10.Basic Hydrologic and Meteorological
11.Flood Hydrology Reports
12.Engineering Design
13.Penstock
14.Construction

3. The project is located at a narrow spot in the Indus River valley
at Tarbela in Haripur.
The main dam wall, built of earth and rock fill, stretches 2,743
meters (8,999 ft.) from the island to river right, standing 148
meters (486 ft.) high.
The spillways, located on the auxiliary dams, in turn consist of
two parts.
The main spillway has a discharge capacity of 18,406 cubic
meters per second (650,000 cu ft. /s) and the auxiliary spillway,
24,070 cubic meters per second (850,000 cu ft. /s).
Now a new diversion dam project is going to start on
Tarbela dam.
Introduction
(Tarbela Dam Pakistan)

4. 1.Site Selection

5. Site Selection continues…..
(Site Selection Front view)
(Site Selection Back view)
(Site Selection top view)
Reasons for selecting this site
 If from the selected point the river flows forward, it will flow
through the valley of steep mountains and will flow again in the
Indus River.
 Advantages :
 There is no need to make tunnel to divert the flow during
construction
 Disadvantage/Environmental Issues:
 A bridge will need to be constructed to replace the road to let the
river flow in Indus River.

6. 2.Site Study
First we will conduct detailed geological and subsurface explorations, which characterize the foundation,
abutments, potential borrow areas and type of Dam selection.
2.1 Geology of the Tarbela area:
 The phyllite unit forms the base of the Kingriali Formation nearly
everywhere in the Tarbella area. This unit was called the "basal
conglomerate member" by Ali (1962, p. 34). It is a gray- and
brown-weathering phyllitic sequence of shale and siltstone.
 Pebbles and cobbles in the conglomerate consist mainly of
Tanawal quartzite but also include phyllite, shale, and vein quartz.
 The dolomite unit of the Tarbela area consists of dark-weathering
interlayered brown and gray microcrystalline dolomite.
 In the Sherwan syncline, distinct layers of undolomitized gray
limestone are present within the dolomite.

7. 3.Dam Type selection
 Site conditions lead to selection of an earth-fill dam
rather than a concrete dam (or roller-compacted
concrete dam) because it includes a wide stream valley,
lack of firm rock abutments, considerable depths of soil
overlying bedrock, poor quality bedrock from a structural
point of view, availability of sufficient quantities of
suitable soils.
 The geology of the dam also supports the construction
of earthfill dam as Shale, Limestone, Siltstone and
dolomite are all soft minerals which when compacted
alongside the soil can produce a strong embankment.
 Furthermore, the earthfill dams are the most common
type of dam, principally because their construction
involves the use of materials from required excavations
and the use of locally available natural materials
requiring a minimum of processing.
 Moreover, the foundation and topographical
requirements for earthfill dams are less stringent than
those for other types
(Earthfill Embankment Dam)

8. 3.1 Technical requirements
 The dam, foundation, and abutments must be stable under
all static and dynamic loading conditions.
 Seepage through the foundation, abutments, and
embankment must be controlled and collected to ensure
safe operation
 The freeboard must be sufficient to prevent overtopping by
waves and include an allowance for settlement of the
foundation and embankment.
 The spillway and outlet capacity must be sufficient to
prevent over-topping of the embankment by the reservoir.
3.2 Administrative requirements
 Environmental responsibility.
 Operation and maintenance manual.
 Monitoring and surveillance plan.
 Adequate instrumentation to monitor performance.
 Documentation of all the design, construction, and operational
records.
 Emergency Action Plan: Identification, notification, and response
sub plan.
 Schedule for periodic inspections..
(Dam Foundation)

9. 4.Embankment
 Many different trial sections for the zoning of an
embankment should be prepared to study
utilization of fill materials; the influence of
variations in types, quantities, or sequences of
availability of various fill materials; and the relative
merits of various sections and the influence of
foundation condition.
4.1 Other Considerations
 Other design considerations include the
influence of climate, which governs the length of
the construction season and affects decisions on
the type of fill material to be used.

10. 5.Geology and foundation conditions
 The foundation is the valley floor and terraces on which the
embankment and appurtenant structures rest Gravel
foundations, if well compacted, are suitable for earthfill
dams.
 Because gravel foundations are frequently subjected to
water percolation at high rates, special precautions will be
taken to provide adequate seepage control or effective
water cutoffs or seals. The liquefaction potential of gravel
foundations will be investigated.
5.1 Comprehensive field investigations and/or laboratory testing will be required
where conditions such as those listed below are found in the foundation:
 Deposits that may liquefy under earthquake shock or other
stresses.
 Weak or sensitive clays.
 Dispersive soils.
 Varved clays.
 Organic soils.
(Weak or sensitive clay)

11. 5.2 Subsurface investigation for foundations should develop the following data
 Subsurface profiles showing rock and soil materials and geological formations, including presence of
faults, buried channels, and weak layers or zones. The RQD is useful in the assessment of the
engineering qualities of bedrock.
5.2.1 Fault
 To the researchers knowledge, there has as yet been no
historic case of an operating dam being displaced by a
fault during an earthquake, although there have been some
"near misses."
 This good record of worldwide performance is particularly
remarkable in view of the fact that many if not most dams
are located in river canyons whose courses are controlled
by preferential erosion along underlying faults and joints.
 Not surprisingly, almost all foundations for large dams
display some faults, however minor, and the geologic and
seismologic challenge is to determine whether such faults
are likely to rupture during the life of the structure (i.e., are
they "active"?) and, if so, with what displacements, with
what geometries, with what magnitudes, and with what
likelihoods
(Real time example of fault)

12. 6. Reservoir investigations
 The sides and bottom of a reservoir should be
investigated to determine if the reservoir will
hold water and if the side slopes will remain
stable during reservoir filling, subsequent
drawdowns, and when subjected to
earthquake shocks
7.Test fills
 In the design of earth and rock-fill dams, the construction of test embankments can often be of
considerable value and in some cases is absolutely necessary.
 Factors involved in the design of earth and rockfill dams include the most effective type of compaction
equipment, lift thickness, number of passes, and placement water contents; the maximum particle size
allowable; the amount of degradation or segregation during handling and compaction; and physical
properties such as compacted density, permeability, grain-size distribution, and shear strength of
proposed embankment materials.

13. 8.Study of causes of dam failure
 An understanding of the causes of failure is a critical element in the design and construction process for new
dams and for the evaluation of existing dams.
 The primary cause of failure of embankment dams in the is overtopping as a result of inadequate spillway
capacity.
 The next most frequent cause is seepage and piping. Seepage through the foundation and abutments is a
greater problem than through the dam.
 Therefore, instrumentation in the abutments and foundation as well as observation and surveillance is the
best method of detection.
 Other causes are slides (in the foundation and/or the embankment and abutments) and leakage from the
outlet works conduit
8.1 Other factors that increase the likelihood of internal erosion and backward erosion
piping incidents developing at a given site include:
 Conduits constructed across abruptly changing
foundation
 Circular conduits constructed without concrete
bedding
 Conduits with an excessive number of joints
 Excavations made to replace unsuitable
foundation
 Conduits with compressible foundations
 Conduits located in closure sections in
embankment dams

14. 9.Flood Hydrograph
 Design-flood hydrographs or parts thereof (peak or volume) are required for sizing the hydraulic features of
a variety of water control and conveyance structures.
 In the case of dams and their appurtenant features, flood hydrographs are required for the sizing of
spillways and attendant surcharge storage spaces
9.1 PMF Hydrograph
 The PMF (probable maximum flood)
hydrograph represents the maximum runoff
condition resulting from the most severe
combination of hydrologic and
meteorological conditions considered
reasonably possible for the drainage basin
under study.
 The PMF is used by design and
construction organizations as a basis for
design in those cases where the failure of
the dam from overtopping would cause
loss of life or widespread property damage
downstream.

15. 10. Basic Hydrologic and Meteorological
 Data-compilation and analysis of hydrologic and meteorological data accumulated during and after severe
flood events is necessary for every flood hydrology study
10.1 Hydrologic Data
10.1.1 Recorded Stream flow Data
 These data are collected primarily by the (Pakistan Geological Survey) at continuous recording stream flow
gauging stations. Generally, these publications present the stream flow in terms of the average daily flow for
each day for the period the stream gauge has been in operation
10.1.2 Peak Discharge Data
 Because the cost of installing, operating, maintaining, compiling, and publishing the data is high, there
are relatively few continuous-recording stream gauges, considering the number of rivers and streams
in the Pakistan
10.2 Meteorological Data
 Systematic acquisition of precipitation data is accomplished primarily through the efforts of the NWS (National
Weather Service). The NWS maintains a network of “first order” weather stations. Each station in this network
collects continuous precipitation, temperature, wind, and relative humidity data.

16. 11.Flood Hydrology Reports
 Envelope curves
 Reservoir routing criteria
 Antecedent flood
 Frequency analysis
 Probable maximum flood
 Snowmelt
 Loss rates
 Unit hydrograph
 Storm study
 Basin description
 General
 Summary of study results
 Authority

17. 12.Engineering Design
12.1Dam Capacity
 Dam capacity = [Reservoir Length x Reservoir Width (at the
dam) x Depth of the Water (maximum)] / 3
 In our case Reservoir Length = 900 meter
 Reservoir Length = 257 meter feet
 Dam height = 15.20 meter
 Total Dam capacity = 900*257*15.20
 = 3,515,760 cubic meter.
 Average pressure = γ * h/2 = 9.81 * 15.20/2 = 74.556
 Length along which pressure acts =
L = h/sin θ = 15.20/ sin 60 = 49.86 m
 Force = pA = 257 * 74.556 * 49.86= 955362.07 KN
 Center of pressure = h/3 from bottom
= 15.20/3 = 5.06 m
12.2 Force & Center of Pressure

18.  Where:
 A is the catchment area in hectares (ha)
 R is the average annual rainfall in millimeters (mm)
 Y is the runoff as a percentage of annual rainfall
 A= 23.13 Ha R=750 mm (average per year) Y= 7.5 %
 Therefore runoff = 23.13*23.13*750*7.5
= 3,009,357 Liters.
Note: Indus basin has never experienced a rainfall of more than
800 mm/year.
12.3 Catchment runoff
 Catchment runoff = 100 *A*R*Y liters
12.4Volume of Embankment
 V = D/6[A1+4M+A2]
 Where M is the area of the cross-section midway
between A1 and A2.
 Height = 15.20 Meter.
 Bottom Length is 2/H.
 Bottom Length = 10.13 Meter
 D = 2.5 meter
 Dam Width = 257 Meter
 Bottom Length = 10.13-2.5=7.63A1 = 17.007* 257=
4370.79 meter square
 A2=A1 M= 2.5*257=642.5 meter square
 V = 4370.79/6[4370.79+4(642.5) +4370.9]
 Volume of Embankment = 8,240,250 Cubic Meter

19. 12.5 Power of Dam
Power The electric power in kilowatts (one kilowatt equals 1,000 watts).
Height of Dam The distance the water falls measured in feet.
River Flow The amount of water flowing in the river measured in cubic feet per second.
Efficiency
How well the turbine and generator convert the power of falling water into electric power. While for
newer, well operated plants this might be as high as 90% (0.90).
11.8 Converts units of feet and seconds into kilowatts.
Power = (Height of Dam) x (River Flow) x (Efficiency) / 11.8
Power = (49.992 feet) x (70962 cubic feet per second) x (0.80) / 11.8 = 258,002 kilowatts
To get an idea what 258,002 kilowatts means, let's
see how much electric energy we can make in a year.
Since electric energy is normally measured in kilowatt-
hours, we multiply the power from our dam by the
number of hours in a year.
Electric Energy = (258,002 kilowatts) x
(24 hours per day) x (365 days per year) =
2,260,097,520 kilowatt hours.
The average annual residential energy use in the
Pakistan is about 1,500 kilowatt-hours for each person.
So we can figure out how many people our dam could
serve by dividing the annual energy production by 1,500.
People Served = 2,260,097,520 kilowatts-hours / 1,500
kilowatt-hours per person) = 1,506,731.68people.

20. 13.Penstock
 Metal pipes will be used in the construction of conduits.
 Steel is a strong alloy of iron and carbon that contains lower
carbon content than cast iron (lower than 2 percent).
 The amount of carbon determines the steel’s hardenability.
Advantages of using Steel pipes
 Welded joints provide water tightness
 High compressive and tensile strength
 Flexible and deformable under stress
 High modulus of elasticity to resist buckling loads
 Various types of joints possible
 Flanges provide a rigid connection to gates and valve
 Has the ability to be easily used as a redundant system
Disadvantages of Steel pipes
 High material costs
 Requires a concrete encasement for
significant and high hazard embankment
 Requires special linings at reservoirs
 The proper selection of linings and
coatings and any associated
maintenance are required to prevent
corrosion.

21. 14.Construction
14.1 Construction of road to access the site
14.2 Leveling and excavation of the damsite
 The site need to be leveled and the required ditching
should be done to make the site ready for the
embankment construction and ultimately dam
construction

22. 14.3 Clearing
 The area to be covered by the embankment* should be pegged out prior to commencement of any works.
 The embankment and the area to be excavated should be cleared and grubbed.
 Topsoil should be heaped in areas outside of the area to be covered by the embankment and all trees,
scrub and roots removed.
 Topsoil should be placed in layers not exceeding 200 mm and planted with grass if it is to be left for a
considerable time (more than 6 months).
14.4 Foundation construction
14.4.1 Grouting
 Grout holes for the cut-off curtain are drilled to a depth where the grout curtain will effectively seal off the
seepage of water beneath the proposed data

23. 14.5 Installing penstocks
 Then the next step is the installing of Penstock.
14.6 Embankment compaction
 All fill material for the embankment should be placed
in layers (or lifts) no greater than 150mm thick.
 The largest size particle should not be greater than
1/3rd the height of the lift, that is, 50mm.
 Each layer should be thoroughly compacted before
the next layer is place
 The compaction effort achieved should be on
average 98% Standard Maximum Dry Density
 The minimum compaction effort should be 95%
Standard MDD
 The material forming the embankment should be
placed with sufficient moisture to ensure proper
compaction
 Before each additional 150mm lift is added to the
embankment, the preceding lift should be scarified to
ensure that the two lifts are properly joined
 A wheeled scraper or truck should be used for
placing the clay on the dam site
(Installing the Penstock)
(Compaction of Embankment)

24. 14.7 Settlement of the embankment
 Settlement of soil banks is common and an allowance must be made for settlement of the dam embankment.
 The embankment may settle to a level where it is overtopped by water and failure will result.
 Or overtime settlement may result in the height of the embankment becoming lower than the spillway.
14.8 Vegetation
 Topsoil should be spread over the exposed surfaces
of the embankment to a depth of at least 150mm and
sown with pasture grass to establish a good cover as
soon as possible.
 Never allow any vegetation larger than pasture grass
to become established on or near the embankment.
 Tree roots, especially eucalyptus tree roots can
cause the core to crack resulting in the failure of the
dam.
 As a rule of thumb, trees and shrubs should be kept
to a minimum distance of 1½ times the height of the
tree away from the embankment of the dam.
 This especially applies to eucalypts.
(Vegetation on Embankment)

25. 14.9 Spillway
The purpose of the spillway is to pass flood flows without overtopping the dam wall. Particular attention must be
paid to providing adequate width and depth (or freeboard) of the spillway as per the specifications given in the
dam permit.
The following guidelines apply to spillways:
 The absolute minimum width of a spillway is three meters.
 Minimum spillway dimensions are given on the permit.