The 163-MW Athirappilly project is not the one-shot pill for our power woes but it definitely is important for the state’s future. The project design had gone through fire; was subjected to the most intense expert scrutiny innumerable times, and had even undergone precautionary design changes just so that the ecology or even the irrigation needs of people downstream are not affected in the worst-case scenario.
It is not a big water-storing project but a run of the river one. The small dam for the project is proposed to be constructed 3 kms downstream from the point where the tail race from Poringalkutthu power house joins with Chalakkudy river. The Athirappilly powerhouse will come up five kilometres downstream, on the left bank of the existing Kannankuzhy Thodu.
Water will reach the powerhouse through a 5-km long tunnel. After power is generated, the water will flow back into Chalakkudy river through Kannankuzhi Thodu, a tributary of Chalakkudy river. The water from Kannankuzhy Thodu will collect above the check dam constructed for Thumboormoozhi irrigiation project. It has been planned to generate 160 MW by installing two 80 MW generators.
Midway change in design
However, it was found that the initial design would dry up Athirappilly waterfalls by the start of summer itself. It was also realised that if there is no adequate flow between the dam and Kannankuzhi Thodu, it could probably affect the aquatic species along the 7.8 km stretch of the river. This prompted planners to rework the design of the project in such a way that the flow in the area is ensured all through the year.
Under the new design, 6.23 to 7.62 mc (cubic metre) of water will be released every second from the dam to the Chalakkudy River. So as not to let it go waste, the new plan envisaged the installation of two 1.5 MW generators right under the dam.
The rain months, however, do not pose any problem. Rainfall received during during June, July and August months will not only lead to an overflow of the proposed Athirappilly reservoir but also, combined with the inflow from nearby Charpa and Idyani streams, would provide enough water right from the base of the dam. The tweak in the design had been carried out as an additional precaution.
If the figures for the last 32 years are taken, it can be found that the catchment area has water equivalent to generate 360 million units of power. The flow comes from three directions. One, the water released after generation in Poringalkuthu. Two, spillover from Poringalkuthu reservoir (this will be 20 times the capacity of the reservoir). Three, the inflow received from the downstream of Porongalkuthu catchment.
The important thing here is, what is stored in the proposed Athirappilly reservoir is a mere 5.5 Mmc (million cubic metre) of water. What this means is that the project uses the flow of the river to generate power. It is this that had prompted Central Electricity Authority to grant techno-economic sanction to the project. Special care has been taken to ensure that the river ecosystem does not suffer from any fundamental changes.
Only 28.62 hectares of forests need to be diverted. 20 tribal families live upstream of the area that will be submerged by the reservoir. 31 persons from these families work on contract basis in KSEB and Forest Department. Orders related to the rehabilitation of these families have been issued way back in 2000 itself. As part of rehabilitation, each family will receive one acre each. Five acres will be allotted for common purposes like toilets and burial. At least one member from each family will be given job during the project period.
Protecting irrigation downstream
Athirappilly project has been envisaged in such a manner that the river water can be put to use for much more than power generation. During summer, the most important function of Chalakkudy River is to nourish the Thumburmoozhi Irrigation Project that services areas lying downstream. The check dam of the project lies below the confluence of Chalakkudy River and Kannankuzhy Thodu. The check dam can store 0.218 Mmc of water. There is a canal on the right and left banks of the River. 2.16 Mmc of water is required daily to pump water along these canals in full capacity.
There is an understandable fear among the local population that the proposed project could bring about a reduction in the water available for irrigation. But this can be avoided if production is done in a controlled manner. During summer, the maximum flow between Athirappilly dam and Thumboormoozhi check dam, except during evening peak hours, will be 6.23 to 7.62 mc. (This has been ensured by a tweak in the design as stated before). Uninterrupted flow, therefore, is assured.
During peak hours in summer, generation in Poringalkuthu and Poringalkuthu Left Bank together have been raised up to 48 MW. In such a scenario, the tail race flow towards Athirappilly project will 36-38 mc. It has been calculated that if water is received at 125 mc per second, Athirappilly project can function at full capacity (160 MW). Therefore, if water is received at 36-38 mc per second for four hours, 160 MW can be generated in Athirappilly for at least one hour.
But, to benefit irrigation downstream, the same input can be used differently to generate 40 MW in four hours. If 160 MW is produced, the water after generation will overflow the check dam and go to waste. But if generation is controlled to 40 MW during peak hours, only 30-32 mc of water will reach Thumburmoozhi causing no spillover. All the water can be used for irrigation purposes.
(The writer is a former KSEB engineer)
