Ill-conceived projects could be disastrous for Aghanashini's ecosystem

Let the river flow

River Aghanashini. Photo by Ashwani Kumar Bhat

A view of the Aghanashini. Photo by Ashwini Kumar Bhat

River Aghanashini, which literally means ‘destroyer of sins’, is one of the few rivers in the country that have remained free from any human intervention so far. However, there have been attempts in recent days to either divert the river or lift and pump the water to irrigate the eastern plains.

The 117-km-long river originates near Shankara Honda in Sirsi of Uttara Kannada district. Some believe that its origin is near Manjanguni, a village 25 km southwest of Sirsi.

Flowing westwards amidst valleys and gorges forming rapids, cascades and waterfalls in the mountainous terrain of the Western Ghats, it drains into the Arabian Sea near the village of Aghanashini in Kumta taluk.

Geographically, the Aghanashini basin is spread over 1,350 sq km. Rocks like granite, gneiss, schist predominate the area and at some places, these are capped by laterite rocks of varying thickness. Interestingly, the rich natural vegetation of the forest in the basin is said to have remained unaltered for 3,500 years, and this makes its estuary highly productive.

The tributaries of the Aghanashini in the western part of the basin, particularly at the right bank catchment, displays structurally controlled rare barbed drainage pattern, which means they flow in opposite direction to the master stream. Such a drainage pattern with unique geomorphological features display varying degrees of gradient till the main river forms waterfall of 108 metre depth near Unchalli village of Siddapur taluk.

But recently, some retired engineers proposed to lift the water of the Aghnashini near Unchalli on the model of Kaleshwaram lift irrigation project in Telangana. And to understand the feasibility and sustainability of the project, it is important to understand the rainfall pattern, hydrological and hydrogeological setup of the Aghanashini basin.

Unscientific project

While the annual normal rainfall in the area where the river joins the sea is 4,500 mm, the rainfall in the eastern part of the basin at Sirsi (near the point of origin) is around 2,500 mm. The 600 sq km catchment area to the east of Unchalli receives a long-term average rainfall of 2,865 mm during the southwest monsoon months (from June to August) and this brings in 61 tmc water. Of this, only 45 tmc (74%) is the run-off near Unchalli falls, while the remaining 26% constitute other components of the hydrological cycle of the area.

Taking this into consideration, the proposal to lift the river water to meet the drinking water requirements and irrigate around nine lakh acres of land in the undivided Ballari, Davanagere and Chitradurga districts seems unscientific. They plan to lift 60 tmc water from the river at Havinabeelu village (near Unchalli) in Siddapur taluk. But, contrary to their estimation, the run-off estimate is just 45 tmc.

Also, the data recorded by the Central Water Commission station at Santeguli in Kumta taluk over the past 10 years shows that the annual flow in the river is 85 tmc and a maximum of 90 to 100 tmc can join the sea. However, those engineers have estimated that 120 tmc of water was joining the sea and this was a 'waste'. This very argument seems unscientific as the circulation of water due to the fresh river water and the tidal influx of the sea oxygenates the water and circulates nutrients.

Further, it is important to note that the already operational drinking water supply scheme to Sirsi town from this river periodically gets affected during the lean season and the problem may worsen if the water is lifted for other schemes.

This apart, blocking the water flow in the river not only affects the natural Unchalli Falls but also the thousands of families dwelling on the banks of the river downstream and in the coastal zone. Needless to say, it will have a profound impact on the fauna, flora and microorganisms along the river and its estuary.

The worst-affected would be the natural development of bivalves, lime shells, variety of fishes, sand deposition and the salt industry. The growth of mangroves in the estuary part too will get curtailed besides saltwater intrusion into the coastal regions.

There also needs to be an evaluation of the perpetual effects the project would have on the socio-economical aspects in the donor basin and the adverse hydro-geological impact it may have over the recipient area.

Tampering with the natural free flow conditions of the Aghanashini by any means shall regionally be ‘an ecological and environmental disaster’.

(The authors are hydrogeologists)