Idukki Arch Dam in the southern Indian state of Kerala is the first of its kind in Asia. It is a Double Curvature Arch Dam impounding Periyar River at a narrow gorge between two granite hills in Idukki, Kerala. In a layman’s explanation – a double curvature arch dam is a dam which is curved both horizontally and vertically towards the upstream i.e. towards the source.

Such type of dams are thinner than ‘earth filled’ or ‘masonry’ dams and are also economical as they require less amount of concrete. They are suitable for narrow gorges as the hydrostatic pressure of the water pressing against its curved surface; strengthens its structure.

The dam is constructed and owned by the ‘Kerala State Electricity Board’ and the water stored by the Idukki curved dam as well as two other dams; Cheruthoni- a Concrete Gravity Dam and Kulamavu- a Gravity/Masonry Dam is used by the Hydroelectric Power Station at Moolamattom (780 MW), which is an underground power station located inside a cave. The approximate distance between the Idukki Arch Dam and the Hydro Power Station at Moolamattom is 43 km and the water from the dam to the station is carried by underground pipes.

Location of Idukki Arch Dam

Idukki Arch Dam is constructed on a narrow gorge also known as the Idukki gorge between two granite hills – Kuravanmala (839 ft) and Kurathimala (925 ft), in Idukki district of Kerala. In local dialects Kuravan means a tribal and Kurathi his spouse, while ‘mala’ is the local word for mountain. The dam is located at an approximate distance of 40 to 50 km downstream of Periyar River from its source.

Nearest railway station to Idukki Dam is Kottayam about a distance of 109 km and nearest airport is the Cochin International airport at a distance of 99 km from the site of the Dam.

The Idukki Dam along with Cheruthoni and Kulamavu Dams hold a huge reservoir which is surrounded by Idukki Wildlife Sanctuary displays nature in its purest form and the view is awe-inspiring.

Legend of Kuravan and Kurathi

There is a small but interesting mythological story told by the locals for centuries about the two hills Kuravan Mala and Kurathi Mala. The legend has it that when Lord Rama and Sita were roaming in the forest during exile; Sita settled to bathe in the spot where the Periyar River was flowing through. The tribal couple Kuarvan (male) and Kurathi (female spouse of Kuravan) accidentally came across the bathing Sita and spellbound by her beauty they were caught staring at her by Lord Rama.

Rama was displeased by their act and cursed the couple to be transformed into rocks (hills Kuravan Mala and Kurathi Mala). However the couple pleaded mercy stating that they cannot even think about a life of separation. Softened by their pleading; Rama told them that they will attain ‘moksha’ or salvation during the Kaliyuga when they will be joined forever.

According to the myth, after the curse they became two hills (Kuravan and Kurathi) and Periyar River started flowing between them and with the construction of the Dam joining the two, the promise which Rama made to Kuravan and Kurathi was fulfilled.

 

History of Idukki Arch Dam – The Idea and Construction

The idea of an arch dam at the location was first conceived as early as 1919 by an Italian engineer Jacob, who submitted a proposal to the Travancore government in this regard; however, the proposal was rejected.

The idea was once again stirred up during a hunting trip of W.J. John- Mallankara estate superintendent and his friend AC Thomas Edattu. The two were on a hunting trip in the location of the present dam guided by the chief of the local ‘Oorali’ tribe. Impressed by the chief’s narration of the legend of Kuravan and Kurathi hills and the impressive flow of Periyar River through the gorge between the hills; Thomas suggested the suitability of the location for construction of an Arch Dam.

Once again in 1932 W.J. John submitted a report to the Travancore government for the construction of an Arch Dam impounding Periyar river at the gorge between Kuravan and Kurathi hills. This time the report included the technical details of utilizing the dam for the purpose of electricity generation.

Later the issue of the dam was notified to the Travancore government in 1935 by the Travancore Assembly member Shri K.A. Narayana Pillai; unfortunately the government didn’t pay much attention to it, although a technical study was conducted by two Italian engineers Angelo Omedeyo and Clantheyo Masele.

It was only during 1947 that the government of Travancore asked its Chief Electrical Engineer- P. Joseph John, to submit a report on dam’s construction; which was submitted to the government the same year. On the request of the Government of India the Central Water commission conducted a detailed investigation of the project in 1956. Consequently the report was prepared in 1961 and the project was sanctioned by the planning commission in 1963. Initial works of the projected started in 1964 under the guidance of Superintending Engineer E.U. Philipose.

The construction of the dam began around five years later on April 30th 1969. Several retired as well as working engineers like C.V. Mathews (Retd. Chief Engineer) were employed to supervise the project. The project was provided long term loan and aid by the Government of Canada and also a Canadian firm of consulting engineers. SNC Lavalin was advising project engineers on Canadian aid. The bid of construction was won by the Hindustan Construction Company (HCC) of Walchand group founded by the Indian Industrialist Walchand Hirachand Doshi.

 

The storage of water in Idukki reservoir commenced in February 1973. Trial run of the first machine was done on October 4th 1975. Finally, on February 12th 1976 the Power Station was commissioned by the then Prime Minister of India Smt. Indira Gandhi.

Technical Details (Civil & Electrical)

Idukki Arch Dam is a double curvature parabolic arch Dam. A Double Curvature Arch Dam is a dam which is curved both horizontally and vertically i.e. the cross section of a double curvature arch dam also looked curved. These types of dams are also known as ‘Shell Arch Dams’ owing to their shape and are suitable for narrow gorges. Idukki Dam is a Concrete Double Arch Dam curved on the upstream side of Periyar River. The thrust of water pressing against the dam’s curved surface compresses and strengthens the dam, also the load on it is transferred to the two ends of dam (the hills) in form of horizontal thrust.

The height of the Idukki Dam is 168.91 mtr (554.2 ft) constructed between Kuravan (839 ft) and Kurathi (925 ft) mountains. The dam is 365.85 mtr (1200.3 ft) long on top with a width of 7.62 mtr (25 ft). The width of the Dam at its base is 19.81 mtr (65 ft). The dam was constructed using around 4,64,000 cubic mtr (16,400,000 cubic ft) of concrete. The Idukki Dam does not have any spill ways and is constructed to store water and has to rely on Cheruthoni Dam which has 9 spillways; to maintain water level.

Idukki Dam along with Cheruthoni and Kulamavu Dam together constitute the Idukki Hydroelectric Power Project. The water stored in huge reservoir of the dams is supplied to the Moolamattom Hydro Power station located at a distance of 43 km from Idukki Dam.

The huge reservoir created by the dams has a total capacity of 55.5 cubic km. (approx 2000 million cubic meters) and a surface area of 60 square km. The Catchment area and normal elevation of the reservoir is 649.3 sq km and 732.6 mtr respectively.

The water stored in the reservoir is diverted to the power station at Moolamattom by a underground network of tunnels and pipes. The power station has a total installed capacity of 780 MW.  It is the India’s biggest hydroelectric power station consisting of 6 (Pelton type) turbine of 130 MW individual capacities. A Pelton Turbine is an impulse turbine which uses the impulsive movement of water for generation of electricity.

The regulated reservoir water drops to a height of 670 mtr (2196 ft) for reaching underground power station. Electricity so generated is transmitted to the states of Tamil Nadu and Kerala by a network of lines and sub stations.

Advantages of Idukki Arch Dam

1) Electricity Generation

The full hydroelectric potential of the Periyar River is used by the Idukki Hydroelectric Power Project which meets the power needs of Tamil Nadu and Kerala. The generated power is supplied to two substations at Kalamassery and Tamil Nadu through a double circuit and single circuit lines respectively also one single circuit line to Pallom.

2) Irrigation

The water released after the generation of power is diverted approx. 20 kilometers to the town of Muvattupuzha through a network of tunnels and channels to be used for irrigational purposes. Muvattupuzha has mainly agriculture based economy and it relies hugely on the water supplied by the Idukki reservoir.

3) Tourism and Wildlife

Idukki is a well sought after tourist destination in Kerala. Located 120 km (approx 75 miles) from Kottayam city; Idukki valley is a beautiful wooded landscape surrounded by small hills and wandering streams. The entry to the dam was initially restricted which was later relaxed for ten days during the festivals of Onam and Christmas. Although at present the duration has been increased to one month during Christmas.

The Idukki reservoir formed by three of its dams- Idukki, Cheruthoni and Kulamavu has a length of 33 km and is surrounded by the Idukki wildlife sanctuary which extends in south east till the town of Thodupuzha and Udumbanchola; the latter bordering the state of Tamil Nadu.  The area of the Idukki wildlife sanctuary is approx. 105 sq km and is home to various animals like- Elephants, Bisons, Sambhars Deers, Tigers etc. The sanctuary is also home to many snake species and birds like Jungle Fowl, Myna, Laughing Thrush etc.

FAQs about Idukki Arch Dam

Q1) Which is the first Arch Dam in India?

Ans- Idukki Dam located in Idukki district, in the southern Indian state of Kerala is the first arch dam constructed in India as well as first in Asia too.

Q2) Where is Idukki Dam located?

Ans- The Dam is located at an approximate distance of 40 to 50 km downstream of Periyar River from its source in the Idukki district, approx. 109 km from Kottayam.

Q3) Which is the nearest railway station and airport to the Idukki Dam?

Ans- Kottayam Railway Station- 109 km; Cochin International Airport 99 km.

Q4) Which river does the Idukki Dam impounds?

Ans- It Impounds Periyar River.

Q5) Idukki Dam is part of which project?

Ans- Idukki Hydroelectric Power Project.

Q6) Which board/company owns the Dam?

Ans- The dam is owned by the ‘Kerala State Electricity Board’.

Q7) Which two other Dams are part of the project along with the Idukki Dam?

Ans- Cheruthoni- a concrete gravity Dam and Kulamavu- a gravity/masonry Dam.

Q8) What type of dam is Idukki Dam?

Ans- It is a double curvature parabolic arch dam.

Q9) Name the hills between which the Idukki Dam is constructed?

Ans- Kuravanmala and Kuratihimala. (‘Mala’ in local dialects refer to hills)

Q10) Who were Kuravan and Kurathi?

Ans- According to the local mythology, they were local tribal couple. Kuravan was a man and Kurathi was his spouse.

Q11) Who cursed Kuravan and Kurathi?

Ans- Lord Rama cursed the couple a.k.a Kuravan and Kurathi.

Q12) Who was the first to propose the idea of a curved dam impounding Periyar?

Ans- The idea was first proposed to the Travancore government by an Italian engineer Jacob in as early as 1919.

Q13) To which government was the first proposal submitted?

Ans- It was submitted to the government of Travancore.

Q14) When and who submitted a report to Travancore government for the construction of an arch Dam for electricity generation?

Ans- W.J. John in 1932.

Q15) Name the Indian politician who brought the issue to Travancore government?

Ans- Travancore Assembly member Shri K.A. Narayana Pillai in 1935.

Q16) Which two Italian engineers conducted a study for the dam?

Ans- Italian engineers Angelo Omedeyo and Clantheyo Masele conducted the study for the dam’s construction.

Q17) Who submitted the project’s preliminary investigation report and when?

Ans- It was submitted by P. Joseph John, the Chief Electrical Engineer, to the government of Travancore in 1947.

Q18) Who did the detailed investigation on the behest of government and when?

Ans- It was done by Central Water Commission in 1956.

Q19) When was the detailed project report submitted to the government?

Ans- The report was prepared and submitted in 1961.

Q20) When did the planning commission accorded sanction to the scheme?

Ans- The planning commission sanctioned the project in 1963.

Q21) When and under whose supervision the preliminary project work started?

Ans- Under the supervision of superintending engineer E.U. Philipose in 1964.

Q22) When did the construction of dam began?

Ans- The construction of the dam began on 30th April 1969.

Q23) Which foreign government provided loans and aids for the project?

Ans- Government of Canada provided long term loans and aid for the project.

Q24) Which company won the bid of construction?

Ans- Hindustan Construction Company owned by Walchand Group won the bid of construction.

Q25) When did the storage of water in the reservoir commenced?

Ans- In February 1973.

Q26) When was the trial run of first machine conducted?

Ans- On 4th October 1975.

Q27) Who and when inaugurated the power station?

Ans- By then Prime Minister of India, Smt. Indira Gandhi on 12th February 1976.

Q28) What is the height of Idukki Dam?

Ans- The height of the Idukki Dam is 168.91 mtr (554.2 ft).

Q29) What is the length of the Idukki Dam on top?

Ans- The dam is 365.85 mtr (1200.3 ft) long on top.

Q30) How much is the top width of Idukki Dam?

Ans- Width on the top of the Idukki Dam is 7.62 mtr (25 ft).

Q31) How much wide is the dam at bottom?

Ans- The width of the Dam at its base is 19.81 mtr (65 ft).

Q32) How much concrete was used for the construction of Idukki Dam?

Ans- The dam was constructed using around 4,64,000 cubic mtr (16,400,000 cubic ft) of concrete.

Q33) How many spillways do the Idukki Dam has?

Ans- Nil – The Idukki dam has no spill ways and it relies on Cheruthoni Dam for maintaining its water level.

Q34) Where is the Hydropower Station located?

Ans- Moolamattom Hydro Power station is located at a distance of 43 km from Idukki Dam.

Q35) What is the unique feature of Moolamattom Hydro Power Plant?

Ans- It is the biggest underground power station in India.

Q36) How much is the total reservoir capacity of the Idukki Dam?

Ans- Total reservoir capacity of the Idukki Dam is 55.5 cubic km.

Q37) How much is the catchment area and elevation of the reservoir?

Ans- The catchment area and normal elevation of the reservoir is 649.3 sq km and 732.6 mtr respectively.

Q38) How is the reservoir water diverted to the power plant at Moolamattom?

Ans- Through a network of underground pipes and tunnels.

Q39) What is the total installed capacity of the power plant?

Ans- The Hydro Power Plant has a total installed capacity of 6 X 130 MW= 780 MW.

Q40) How much drop does the water encounters before reaching the power plant?

Ans- The regulated reservoir water drops to a height of 670 mtr (2196 ft).

Q41) Which two states is the electricity so generated is transmitted?

Ans- Tamil Nadu and Kerala.

Q42) Which other town does the dam supplies water for irrigation?

Ans- To the town of Muvattupuzha around 20 kilometers from the dam.

Q43) Name the wildlife sanctuary surrounding the Idukki reservoir?

Ans- Idukki Wildlife Sanctuary.

Q44) When does the dam opens for the tourists and for many days?

Ans- The dam opens for a month around Christmas.

Q45) What is the area of the wildlife sanctuary?

Ans- The area of the sanctuary is around 105 sq Km.

Q46) Name some species found in the sanctuary.

Ans- Wild Boar, Bison, Barking Deer, Elephants, Tigers, Jungle Fowl, Laughing Thrush etc along with various species of snakes.