Pamba Dam
Pamba Dam is a gravity dam built on the Pamba river in the Ranni forest area of Seethathodu panchayat in Pathanamthitta district of Kerala, India. It was built in 1967 as part of the Sabarigiri Hydroelectric Project. Sabarigiri Hydro Electric Project is the second largest hydro electric project in Kerala. Pamba dam's reservoir is connected to the nearby Kakki dam's reservoir by a long underground tunnel. The dam is long and high and is located at an elevation of above sea level. The dam is located in a forest area adjacent to the Periyar National Park. The water stored in the Pamba and Kakki dams is conveyed to the Sabarigiri powerhouse through penstock pipes. The dam was commissioned in 1967.
History
The Project plan was to create a reservoir by impounding Pampa River and another reservoir by impounding Kakki River and connecting both the reservoirs by means of a tunnel to form a connected reservoir. Preliminary work and investigation were done in 1958, and the dam construction was started in 1960. Masonry work started in 1961. Completion of dam as per the 1960 schedule was in 1964. Actual completion of the total project was in 1967. Tools and plants, both indigenous and imported, were used in the construction of the Pamba dam. Natural sand was not available in the nearest localities and hence, except in the case of power house, crushed sand was used. For this purpose, eight crushing and screening plants were installed. As a trial and error, 10 to 20 per cent river sand was mixed with the crushed sand to bring the fineness modulus, but the improvement was not good enough. So, new screens were built and fitted. Due to river diversion problems, difficulties related to excavation in the river bed was delayed. Because of that, the progress of masonry construction was below the target. Sand was collected from the upstream and downstream of the river, then was washed and used until the crushers came into operation.Cement for the dam came from Thulukkapatty in Tamil Nadu and the main storage of cement was at Theni, from where the cement was transported to the dam site and kept in the departmental cement store.
Excavation for the dam
It was assumed that there will not be much excavation to be done. But in reality this had increased much and a quantity of 4,92,000 cubic feet of earth work excavation had to be done for the dam foundation. Disintegrated rock and boulders had to be removed and foundation taken to deeper levels. Machineries could not be used and manual labor had to be used.River bed excavation and coffer dam
To take up the excavation in the river bed, a masonry coffer dam was constructed. The top width of the 285 dam was 2 feet to 2.5 feet and the maximum height was 20 feet.Concrete foundation and spill way
It was originally proposed to be constructed with cement mortar blended with 20 per cent surki. But after finding from laboratory tests that sufficient strength had not been achieved by using surki, Cement was used instead of surki.Dam Features
- Type of Dam: Masonry – Gravity
- Classification: HH
- Maximum Water Level : EL 986.33 meters
- Full Reservoir Level : EL 986.33 meters
- Height from deepest foundation: 57.00 meters
- Length: 281.48 meters
- Spillway: 6 No. radial gates, each of size 7.0 x 4.87 meters
- Crest Level: EL 981.46 meters
- River Outlet: 1 No., Hollow jet valve, 1.8 m diameter
- Name of Project: Sabarigiri HEP
- Purpose of Project: Hydro Power
- Year of completion: 1967