B. Kavitha*
* M. Phil., Scholar, Department of History, S. T. Hindu College, Nagercoil.
Abstract
The Perunchani Dam was built in the year 1948 across a picturesque valley between low hillocks through which the river Kodayar now flows. The catchment area and the surroundings are hilly, ever-green forest regions. The total length of the dam is 1137 feet of which the main non over flow dam is 903 feet long. The maximum height above the deepest foundation is 137 feet, while the height over average bed level of the river is 84 feet. The volume of the dam was estimated at 18,29,200 c feet. The dam was built of rubble masonry in cement mortar with coursed spilt stone masonry for the outer faces. Four proportions of cement mortar were used for the dam masonry. On completion of the dam the whole area was converted into a beauty spot and a centre of attraction for tourists and picnic parties. Persons of repute in the profession like Dr. J. L. Savage and Dr. K. L. Rao were consulted at various stages of the construction and their timely advice had been beneficial in accelerating the progress of the scheme. Their remarks about the nature of work done here bear ample testimony to the high standards insisted on in the construction.
Introduction
The Perunchani Dam is located South-East of Trivandrum at a distance of about 36 miles by road and about 6 miles East of Kulasekharam. It is built in the year 1948 across a picturesque valley between low hillocks through which the river now flows. The catchment area and the surroundings are hilly, ever-green forest regions.
Perunchani Dam details
The total length of the dam is 1137 feet of which the main non over flow dam is 903 feet long. The maximum height above the deepest foundation is 137 feet, while the height over average bed level of the river is 84 feet. The crest level of overflow section ie., the full reservoir level stands at 300.0, while the top of the dam is at 309.00. The maximum water level is limited to 306.00 when the area of reservoir will be 2300 acres. The area at full reservoir level is 2137 acres or 3.34 sq. miles. The drawn off capacity will be 2300 m.c feet. The maximum width of dam at foundation level (+195.0) is 86.5 feet, while the width at top is 16 feet. The volume of the dam was estimated at 18, 29, 200 c feet.
The dam was built of rubble masonry in cement mortar with coursed spilt stone masonry for the outer faces. Four proportions of cement mortar were used for the dam masonry. A mix of 1:2 1/2 was used for the front 6ft. from the vertical face of dam and 1:4 was used for the near portions up to a level 270.0 while the higher levels the corresponding mixes were 1:3 and 1:5 respectively. Construction joints with copper strips having “U” shaped bends were provided at about 85 ft. intervals in the body of the dam and the space around them filled with asphatt. The face of the masonry at the construction joints were built staggered and special types of precast concrete blocks to suit the particular shape at the corners have been used to afford facility for the spady progress. Concrete cut off trenches wherever necessary on the water side, a drainage inspection gallery 5 ft x 7 1/2 ft. inside body of the dam, drainage culverts and clay puddle on the up steam side with rip rap filling on the rear deal with the seepage water and add to the safety of the structure. Two vent ways of size 6ft x 8ft. each with a discharge capacity of 700 cusecs were provided. These under sluice weighing 61/2 tone each were controlled by winches which can be operated both by manual labour and electric power. As an additional feature emergency shutters of a simple design were also provided. The supply and errection of shutters were carried out by a German Firm.
Except for the use of simple machines like concrete mixers, haulage lines, tripping waggons, hand-winches, the construction works were carried out entirely by manual labour and indigenous improvisations. Dressed stones were used on exposed portions and where water flowing at high velocity has to be tackled.
On completion of the dam the whole area were converted into a beauty spot and a centre of attraction for tourists and picnic parties. Throughout the period this work had been in progress and it is a point of special interest to note that only local labour had been engaged which had contributed considerably towards economy. Another point worthy of mention is that only the minimum supervising staff have been engaged on this work compared to other similar projects elsewhere. Persons of repute in the profession like Dr.J.L.Savage and Dr.K.L.Rao were consulted at various stages of the construction and their timely advice had been beneficial in accellerating the progress of the scheme. Their remarks about the nature of work done here bear ample testimony to the high standards insisted on in the construction.
The ancient Tamils had classified this part of the land into three categories namely, Malai Nadu (Mountainous Country), Edanad (Middle country) and Nanjil Nadu (Land of Nanjil or paddy field), while the entire Vilavancod Taluk and part of Kalkulam were designated as Malai Nadu; part of Kalkulam and the land head reaches of Thovalai were identified as Edanad. The rest of its, namely part of Thovalai and Agasteeswaram are known by name Nanjil Nadu. While gravelly type of porus soils were more predominant in the head reaches, alluvial soils were identified in the lower plain reaches of the district which were found more suitable for agricultural operations than other type. As such from time-immemorial paddy cultivation had come to stay in the lower parts of the district.
The ancient literature speak of the uncommon richness of the soil, the consequent superfluity of filling it and the large volume of water that is discharged into the sea carrying in its flow flowers of variegated colours.
Construction Details
This is a solid gravity dam with a surplus regular of 4 vents (12.19 m x 4.57 m). The dam is built of Random Rubble Masonry in Cement Mortar upstream face of dam Cement Mortar 1:21/2 and 1:3 are used below and above 270.00 respectively. In the downstream face Cement Mortar 1:4 & 1:5 are used. The front and rear faces are of hammer dressed stones of rectangular shape with hearing of random rubble.
A drainage gallery 1.5×2.25 m has been provided in the mid river section for a length of 45m. for the remaining length of dam 0.60 x 0.60 m drainage duct connecting the vertical drainage, shaft has been provided. Construction joints has been provided at 7.5 m intervals in the body of the dam.
Safety Measures
In the year 1992 during flood, the dam experienced an inflow of 936 cumecs as against designed flood of 895 cumecs and free board was encroached upon.
Hence the dam safety paned proposed to convert the existing open weir available on the left end of the dam into a gated spilt way (i.e. 3 additional vents of size 12.20 m x 4.57 m).
While providing additional vents it is necessary to strengthen the dam by providing backing concrete to non spill way portion for stability of the existing masonry dam.
Hence this estimate is prepared with following provisions
1. Clearing scrub jungle.
2. Chipping and wedging
3. Earth work open excavation
4. Removing hard rock
5. Benching hard rock
6. Drilling 75 and 35 mm bore holes for foundation
7. Cleaning and water testing
8. Grouting bore holes
9. Providing anchor rods of 25 mm dia
10. Raking out joint 20 mm
11. Providing bitaments point
12. Providing towel rods of 20 mm dia
13. Providing M20 for gallery
14. Providing M10 backing concrete
15. Supplying fabricating steel
16. Refilling foundation with excavated earth
17. Provision for Photographic, vedio, tender, P.S. and diversion channels formatting changes.
This estimate is prepared based on the current schedule of rate for the year 2007-2008 and works out to Rs. 11.50 crores. It can be chargeable under the head of account.
Conclusion
As there was deficiency in the Kodayar System, Perunchani Dam was constructed in the upstream of Pandian Dam in 1953 to store flood water in Paralayar river. The dam was also raised, strengthened and improved during 1964-70 to take additional storage by raising the full reservoir level by 1.83 m. Vast forest areas have been cleared in Keeriparai, Pechiparai, Perunchani and the surrounding regions for raising Rubber Plantations which are further extended. It is very essential to protect the rich but vanishining flora of in and around Perunchani.
References
1. V. BALACHANDRAN and G. RAMALINGAM, Geological Document on Perunchani Dam and its Appurtenances, Kanyakumari District, 1997.
2. M. GOPALA KRISHNAN, Gazetteers of India Tamil Nadu Kanniyakumari District, Madras, 1995
3. V.GOPAL SAMY, Executive Engineer, PWD History of Perunchani Dam, Nagercoil, 1987.
4. Chief Engineer (Investigation) Public Works Department, Madras-Report, dated 23.1.1989.
5. G.O.Ms.No.193 Public Works (R1) Departments, dated.15.03.1993.
6. Report of the Estimate for providing Additional for spill way at Perunchani Dam in Kanyakumari District in Tamil Nadu, 2007-2008.
7. Copper Plate Inscription in Perunchani Dam, 2nd September 1953.