Srisailam Dam - History, Technical Details and Rare Photos

The Krishna River raging through the radial crest gates of Srisailam dam, Aug 14, 2019

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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.

The Krishna River basin. The location of Dams constructed across the Krishna and its tributaries are labeled using push pins in red. Reproduced with permission from creator Pradeep Macherla. HQ can be found here.

The foundation stone for Srisailam dam was laid by the then Prime Minister Late Shri Pandit Jawahar Lal Nehru on 24th July 1963. Funds were mobilized through a loan from the World Bank

                                                         

                                                          

After almost 20 years of construction, the then Prime Minister Smt. Indira Gandhi inaugurated the dam in October 1982.

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.

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.

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.

Kanuri Lakshman Rao, the father of India's water management and agriculture is the architect of Srisailam Dam.

Kanuri Lakshman Rao, the father of India's water management and agriculture is the architect of Srisailam Dam.

Top: When the construction of the concrete wall was about to start

Bottom: After construction is finished.

When the upstream coffer dam construction just finished. Coffer dams are built to prevent water flow and make the area dry for construction.

Srisailam Right Power House work in progress.

When excavation of the foundation is in progress.

Plunging pool work in progress. Plunge pools absorb the impact of water from spillway gates.

The D/S concrete wall

The D/S concrete wall

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

When the construction of spillways just finished

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.

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.

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.

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.

The "Gallery "of the Dam
Top: The steps way to the foundation gallery (495ft)
Bottom: The top gallery (780ft).

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).

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.

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).

Top: The construction of a turbine using giant steel ferrules.
Bottom: Model of turbines and penstocks of Srisailam right powerhouse.

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)

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.

Some aerial footage of Srisailam dam curated from newspapers.
Top and Middle: Aerial images obtained during the Krishna Floods, 2009
Bottom: Drone image obtained when gates opened 2017.

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)

August 14, 2019

August 14, 2019

Many Telugu language movies were shot in the backdrop of Srisailam Dam. Below are some of the well know movies (Hyperlinked to YouTube)

1) Bangaru Panjaram starring Shobhan Babu and Vanishri , 1969

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

Let me know in the comments sections if there are any errors in technical details or usage of terms.