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I was brought up in Srisailam Project
(Local name Sunnipenta). I lived there for 23 years before moving to Bengaluru
after my mother's retirement in 2012. My parents (Late S.V.S. Subrahmanyam and G.
Syamala Devi) moved to Srisailam in the 1960s as teens in search of jobs as the
project was about to begin. Both my parents worked in the Irrigation Department
of Andhra Pradesh until retirement. I have been thinking about writing something
like this for many years but could not manage the time to do so. Recently when
I was digitizing old photos, I found several rare photos of Srisailam Dam, and
those photos motivated me to write this up. All the photos and the documentary
video were collected by my father.
History of Srisailam Dam
Srisailam Dam is located in the middle of the Nagarjuna Sagar-Srisailam Tiger Reserve, the largest tiger reserve in India. Srisailam dam is also called Neelam Sanjiva Reddy Sagar Project (NSRSP), named in honor of the first Chief Minister of Andhra Pradesh, Late Neelam Sanjiva Reddy (1956-60 and 1962-64). Though the dam acts as a bridge between two states, the maintenance is under the control of Kurnool District, Irrigation Department of Andhra Pradesh. The mega project was constructed across river Krishna which is the fourth largest and second largest river in India and South India, respectively with ~1288km length of which ~720km in AP and TS. The river originates in the Western Ghats of Mahabaleshwar, Maharashtra, and terminates in Hamsaladeevi, Krishna district of AP. Four states (MH, KA, TS, and AP) are dependent on the Krishna water for irrigation and hydroelectric power generation. Several dams have been constructed across the Krishna River since independence.
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After almost 20 years of construction, the then Prime Minister Smt. Indira Gandhi inaugurated the dam in
October 1982.
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India's First Prime Minister Jawahar Lal Nehru laid the foundation for the mega project. On the left is Neelam Sanjiva Reddy, the first chief minister of Andhra Pradesh. On the right is G.A. Narasimha Rao, Chief Engineer of the Project. |
This is the second-largest and second-highest dam constructed across the Krishna River (the first being Nagarjuna Sagar Dam). It is a gravity dam that depends entirely on its own mass for stability.
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Top: The most recent Google earth 3D image of the dam Bottom: The Aerial 3D model of the dam developed much before satellite
imagery! |
The main purpose of the project was to generate hydroelectric power from the two powerhouses constructed on either side of the dam called Srisailam Right Bank Power House (SRBP) and Srisailam Left Bank Power House (SLBP). Now after the bifurcation of AP state, the SLBP went to TS while AP retained the SRBP.
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| The topographical representation of the dam and the
two powerhouses, the one on the left (concerning water flow) is now part of
TS while the one on the right is part of AP. Blue lines represent the water flow
through turbines for power generation. Image sourced from Japan International Cooperation Agency. |
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Top: When the construction of the concrete wall was about to start |
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When the upstream coffer dam construction just finished. Coffer dams are built to prevent water flow and make the area dry for
construction. |
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Srisailam Right Power House work in progress. |
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When excavation of the foundation is in progress. |
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Plunging pool work in progress. Plunge pools absorb
the impact of water from spillway gates. |
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| Top and Bottom images show the water flow over D/S concrete wall during floods in the river the Krishna dated 29-July-1967 at 4PM |
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| When the construction of spillways just finished |
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| Water flowing over spillways due to flood, gates are not fixed yet |
In the above image, if you observe carefully, the
sluice gates are opened. Sluice gates help in flushing out the sand sediments
brought by flood.
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| Inauguration of the project by the then Prime Minister Late Smt. Indira Gandhi, 1982. Both my father and mother received one month's bonus on inauguration. |
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This image was probably captured first the time when
the gates were fixed and opened in 1984. Both my father and mother received
half a month's bonus on opening of gates. |
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| When the sluice gates opened during maintenance. |
Srisailam Dam has an Ogee type of spillway, by design, the end of the spillway has a mini tank-like structure called a bucket
(apron) and a stilling basin. The water
discharged through spillways has potential energy that converts into kinetic
energy of immense magnitude. The stilling basin acts as an energy dissipater and
reduces the velocity of the flow by evaporating water (header image of this
article), thereby preventing erosion of the river, channels, etc., and safeguarding
the foundation.
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The "Gallery "of the Dam |
The gallery of the dams provides
provision for inspection of seepage from the reservoir to the downstream of the
dam. Seepage is common in such mega projects and has to be frequently
monitored. Thanks to my father, I have visited the gallery numerous times since
childhood. The experience is surreal. Lifts are installed to visit the gallery.
There are three gallery levels for Srisailam Dam (the first one at 780ft is called the top gallery, the second at 680ft is called the intermediate gallery and the third at
495ft is called the foundation gallery). I remember visiting the deepest foundation
3rd level gallery in childhood, it is full of knee-level water. Due to a lack of lift maintenance, a few people are allowed to the deepest level only for monitoring. Many people can visit the top gallery with permission
from the Irrigation Department of Andhra Pradesh (Not when the gates opened).
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| View of spillway gates discharging flood water as seen from level one gallery, Aug 2019. The water flow direction is reversed and upwards due to the bucket (apron) and stilling basin that reduces velocity as discussed earlier. |
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The instrumentation of the Srisailam dam. The
dam is divided into 22 blocks in total. The dam is fitted with various instruments like thermometers, pressure cells, rock displacement meters, etc. These instruments provide the condition of the dam and are useful for monitoring safety. For example, thermometers provide the temperature of the concrete. Temperature fluctuations result in the contraction or expansion of concrete affect volume and cause cracks. You can see in the above image obtained in Aug 2019, some of the instruments are not working (labeled in red). 
Historic 2009 Krishna River Floods Srisailam Dam witnessed unprecedented floods in
2009 which were estimated to occur once in a century. The reservoir water level
breached 885ft for the first time and reached 896ft with a peak average inflow of
nearly 26 lakh cusecs, double the amount of water that can be
discharged through radial crest gates. "On October 3, 2009, the dam was
subjected to maximum stresses for the first time after its commissioning in
1983-84. The dam tilted downstream by 4 mm and the tilt reached a
maximum of 8.8 mm on October 8, 2009. Fortunately, it returned to normal after
the flood receded." (The Hindu)  |
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| From the viewpoint of the historic 2009 Krishna
River floods, the water level has breached the full reservoir level of
885ft. |
If you observe carefully, the dam is slightly
arched. But the Srisailam dam is not an Arch dam ( a different type of dam ). The abutment rocks were not considered competent enough to take the arch thrusts which is common in the arch dam’s design.
The project serves as a major irrigational source for the Kurnool, Kadapa, and Prakasam districts of AP (via Srisailam Right Bank Canals and balancing reservoirs like Velugodu) and Mahabubnagar, Wanaparthy, Gadwal, Nagarkurnool & Nalgonda districts of Telangana. Several lift irrigation projects were also constructed: Pothireddypadu (AP), Kalwakurthy lift irrigation (TS), and under construction: ~40km tunnel Veligonda project (Gravity feed, work in progress, AP) and Srisailam left bank canal via 51km underground tunnel (Gravity feed, work in progress, TS) to fill lakes during monsoon periods.
Drinking Water Fact: Approximately ~10TMC of water is allocated to Chennai metropolitan city via the Telugu Ganga project for drinking purposes. The water through various canals reaches Poondi reservoir near Chennai.
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Some aerial footage of Srisailam dam curated from
newspapers. |
You can find more details of the dam in the documentary video below; the narration is in Telugu.
The Salient Features of Srisailam Dam (Technical)
Dam and Spillways
Dam type: Gravity dam
Height from foundation: 145.70m
Length of the Dam: 512m
No. of Blocks: 22
Spillway Type: Ogee Spillway
Number of Spillway Gates: 12
Gates type: Radial Crest gates
Radial Crest Gates Discharging Capacity (All
together): 13.55 lakh cusecs
Width and Height of Radial Crest Gates: 60ft width
and 55ft height
Number of Sluice Gates: 2
Sluice Gates Discharging Capacity: 0.35 lakh cusecs
Width and Height of Sluice Gates: 12ft width 30ft
height
Reservoir Details
Water Level and Gross Storage Capacity: 885ft
and 215.81 TMC
Minimum Water Level for Irrigation Purpose: 854ft
(89.29 TMC)
Minimum Water Level for Power Generation: 834ft
(53.85 TMC)
Dead Storage: 705ft (3.41 TMC)
Water Spread Area: 612.42 Sq Km
Tail Water Level Maximum: 635ft
Tail Water Level Minimum: 535ft
Flood Design (1000 year Frequency): 19 lakh cusecs
Maximum Flood Observed: ~26 lakh cusecs (October
2009)
Power Generation Details
Two powerhouses
Srisailam Left Bank Powerhouse (TS)
Srisailam Right Bank Powerhouse (AP)
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Many Telugu language movies were shot in the
backdrop of Srisailam Dam. Below are some of the well know movies (Hyperlinked
to YouTube)
2) Krishnaveni starring Krishnam Raju and Vanisri,
1974
3) Criminal starring Nagarjuna, Manisha Koirala and
Ramya Krishna, 1994
4) Rakshakudu starring Nagarjuna and Sushmita Sen,
1997
5) Master starring Chiranjeevi, Rohini and Sakshi
Sivanand, 1997
6) Suryavamsam starring Venkatesh, Radhika and Meena, 1998
The above screen grab is from BBC drone footage of the dam shot recently when the gates were opened, you can find the video below
Finally, you can view my recent Srisailam Trip Photos from Aug 2019 here at HQ
