Clearing the air on water: On Parambikulam Aliyar Project

Synopsis: With political will, Kerala and Tamil Nadu can overcome hurdles to renew the Parambikulam Aliyar Project agreement.

What is Parambikulam Aliyar Project?

It provides for the diversion of 30.5 thousand million cubic feet (tmc ft) annually from Kerala to Tamil Nadu. This major project with an outlay of ₹138 crore was completed in 1972. The project is also an example of co-operative federalism.

Background: The PAP agreement was signed between Kerala and Tamil Nadu on May 29, 1970, with retrospective effect from November 1958.

The agreement ensures Kerala’s riparian share in the Sholayar and Chittoorpuzha sub-basins as a guaranteed annual entitlement without applying the distress-sharing formula. It also ensures four months’ flow (from the Northeast monsoons) from the Upper Nirar for Kerala’s exclusive use in the Periyar basin.

Except for the Kerala Sholayar dam, the Parambikulam, Peruvaripallam and Tunacadavu dams are situated inside Kerala territory but are controlled and operated by Tamil Nadu.

Aims and objective: Using inter-basin diversion, the project irrigates drought-prone areas in the Coimbatore and Erode districts of Tamil Nadu. The project paved the way for surplus waters from eight west-flowing rivers to irrigate eastern Tamil Nadu.

What is the issue?

Kerela’s reservation: Kerala has reservations on the non-realisation of its share of 2.5 tmc of water from the Parambikulam group of rivers for the exclusive use of Chittoorpuzha valley.

The failure of Tamil Nadu: Tamilnadu failed in giving Kerala what it is entitled to at the Manacadvu weir and Sholayar dam in low-yield years from the reservoirs under its control and construction of some structures in the project area without Kerala’s concurrence.

New constructions: Tamil Nadu regrets the non-realisation of the anticipated yield of 2.5 tmc from the proposed Anamalayar project and the expected yield of four months of flow from the Upper Nirar. It also proposes new constructions to augment its share which have not got Kerala’s consent.

Inconclusiveness: The deliberations are so far inconclusive because both States have focused on the total average yield and are not exploring furthering the utilisable yield from the available yield. There is huge variation between the actual yield, the anticipated yield, and also the yield available for utilisation.

What does a closer look at the project hydrology reveals?

Loss of water: Of the last 20 years, the Chalakudy basin experienced overflow from PAP in 12 years. Similarly, a sizeable portion of the water is lost through Manacadavu as unutilisable flows.

Poor storage and the skewed inflow pattern: Kerala had consented to the diversion in the 1960s, anticipating enough storage spaces in both the Periyar and Chalakudy basins to meet its needs, but most of those storage reservoirs were subsequently denied environmental approval.

What is the way forward?

First, experts of both States could analyse and create working tables based on the observed flow regime to see how much additional water can be made available in the system through new reservoir systems and how that can be shared.

Second, it is imperative that proper checks and balances be agreed upon to ensure the guaranteed entitlements at Sholayar and Manacadavu. The political leadership can deliberate on the principles of sharing to review the agreement.

Source: This post is based on the article “Clearing the air on water” published in The Hindu on 27th October 2021.