Friday, December 30, 2011

Periyar Irrigation Project Status as in 1907

The status of the dam and the Periyar Irrigation Project as obtaining in 1907 (12 years after commissioning of the dam) is fairly described in a letter from E.P.Holton and published in the Scientific American of September 7, 1907.

It is mentioned in this letter that the project work was closed on October 11, 1895 (when the dam was commissioned) and water was let into the (Vaigai) channels on June 20, 1897. Nearly 50,000 acres were brought under irrigation in the first year, increasing to 150,000 acres (as in 1907), bringing in a net income of 4% on the total investment of $ 3.33 million.

"The dam is 1241 ft long, 176 ft high above the bed of the river, 144 ft 6 in wide at the base and 12 ft thick at the crest. The front and rear walls are of rubble masonry and the core of surki mortar concrete. The spillway is over a saddle on the right bank, 434 ft long and blasted down to 22 ft below the crest of the dam. On the left bank there is an extension of the main dam, 221 ft in length to close a smaller saddle."
It is also mentioned that there was leakage in the dam which has dropped from one-fourth to one-twelfth of a cubic foot a second.  Further it is mentioned that the percentage of lime in the water has decreased considerably after the first two or three years.

Of special interest is the mention that there is heavy tropical downpour in the area over 300 sq miles of mountainous catchment area with recorded rainfall over 200 inches, with showers of 6 inches at a time, increasing the normal flow of 2000 cusecs to 120,000 cusecs.

The letter also mentions about the two improvements under consideration then:
1. Generation of electricity utilizing 50,000 HP of the diverted waters.
2. Increasing the storage capacity and making available more of what is stored.
For increased utilization of available storage, it is mentioned that the current water cutting 6000 ft long, 21 ft wide from the lake connecting to the tunnel, is being widened to 35 ft and being lowered to the sill level of the sluice (ie. 106.68 ft above datum) to give an additional 9 ft of gain in available supply.
To increase storage capacity, sluice gates at the spillway are set up to make available 10.2 tmc of live water storage for use.

-Joseph Ponnoly

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