GUWAHATI, Sept 11 - The Central Water Commission (CWC), in its 46-page study report on Kerala floods of August 2018, has recommended that it is essential to review the rule curves of all the reservoirs in Kerala.
The rule curves of the Kerala reservoirs need to be formulated for both conservation and operations as well during the flood, particularly for the reservoirs having the live storage capacity of more than 200 MCM, in order to create some dynamic flood cushion for moderating the floods of lower return periods, particularly in the early period of monsoon, it says.
Rule curve is one of the most commonly used tools to aid reservoir operation. It means the division of the useful volume of the reservoir in zones with different strategies for water supply for different uses. Rule curve is generally used to limit the reservoir operations in flood control, the maximum height of the stored water, preventing collapse in supply, etc.
The CWC recommendations in this regard have implications for the NE region, which has several hydroelectric power projects under operation and has the proposal for installing over 150 more hydel projects in the near future.
It perhaps needs no mention here that the phenomenon of climate change has been upsetting the entire rainfall regime of the Indian subcontinent and incidences of heavy to very heavy rainfall activities have been gradually increasing here, along with the lengthening of the list of the number of rainless days.
In Kerala, of the total 758.6 mm rainfall between August 1, 2018 and August 19, 2018, about 414 mm rainfall occurred in just three days, that is � on August 15, 16 and 17, 2018. This created severe flooding in the state. Due to severe rainfall from August 15 to 17, the gates of about 35 dams were also opened because of extremely large inflow of water in the reservoirs. Last month, the reservoirs were either at full reservoir level (FRL) or only few feet below the FRL.
During August 15-17 last, the three-day rainfall depths realised in Periyar, Pamba, Chalakudi and Bharathapuzha sub-basins were 588 mm, 538 mm, 421 mm and 373 mm respectively and these depths are of the same order as that of the 1924 rainfall over the State, says the CWC.
From the analysis it has been found that the dams in Kerala neither added to the flood nor helped in reduction of flood, as most of the dams were already at FRL or very close to FRL on August 14 last, due to more than normal rainfall in the months of June and July. Had the reservoir been a few feet below FRL, the flooding conditions would have not changed much, as the severe storm continued for three days and even for four days in the majority of the places, and in any case, it would have been necessary to release from the reservoirs after the first day of the extreme rainfall, says the above CWC report.
In this context, it is pertinent to mention here that environmentalists maintain that despite repeated assurances, the authorities have been granting clearances to the NE hydel projects without prior downstream impact and risk assessment studies. The latest examples in this respect include the 1750-MW Damwe Lower Project coming up on the Lohit River and 2880-MW Dibang Multipurpose Project coming up on the Dibang River, they say.