Have you ever wondered what is the age of our rivers? For instance, did you know that the rivers that flow in Karnataka are older than the mighty Himalayas?
Karnataka Water Resources Department has classified the state’s rivers into seven major systems: Godavari, Krishna, Cauvery, North Pennar, South Pennar, Palar, and all the west-flowing rivers. As a matter of fact, the west-flowing rivers, though many in number, account only for 12.73% of the state’s drainage area while the six major river systems account for 87.27%. So, why do most of these rivers flow eastward? There is a bit of geological history to this, rooted in the Western Ghats where most of Karnataka’s rivers originate.
Over 180 million years ago (mya), all of today’s land mass (most continents) was merged together as a supercontinent called Gondwana land. Owing to a certain geological event, it split and one of them was the Peninsular Indian plate that drifted northward for about 100 mya to eventually hit the Asian plate about 45 mya, which resulted in the formation of the Himalayan mountain range. During its movement, it passed through the present-day Reunion Islands which had a volcanic centre in the Earth’s lithosphere over 200-300 km across. As it passed through this region, it generated basaltic magma resulting in the uplift of what is now the Western Ghats and tilted the Indian plate in the easterly direction. Thus, the Western Ghats are not true mountains but faulted edge of a raised plateau.
By the time peninsular India ended its northward drift and collided with the Asian mainland (between 45 and 65 mya), the Western Ghats was very much in place. All this permanently cast the drainage pattern. Thus, in Karnataka, most of the rivers originate in the Western Ghats and drain into the Bay of Bengal. The Cauvery is the largest river in the state and originates from Talakaveri in Kodagu district.
Ecology and biodiversity
The geological origins of the rivers in the Western Ghats have also helped nurture a unique ecosystem. The mountain ranges comprise high-altitude grasslands, sholas, wet evergreen, semi-evergreen, moist deciduous and dry deciduous forests. And as one moves eastwards towards the plains, a bulk of the plateau is scrub — grassland with occasional dry deciduous forests. Yet, these regions form the catchment area and are part of the river hydrology that is responsible for capturing the incident rainfall and draining them off. Most of the west-flowing rivers are perennial while the east-flowing rivers depend on the monsoons. During all these cycles, life in various forms is nurtured and supported. These unique landscapes are home to several species of plants and animals found nowhere else on Earth.
India, being an agriculture-dominated country, has over 70% of the population directly or indirectly dependent on rivers for food and livelihood. In Karnataka, the east-flowing rivers originating from the forests of the Western Ghats and traversing thousands of kilometres on the downstream journey to the Bay of Bengal provide food security to hundreds of towns and villages in southern Peninsular India. These river systems not only provide water for household consumption and irrigation, but also for the generation of electricity. Massive irrigation projects in the Rivers Cauvery, Krishna and Godavari serve as the granary of the Deccan plateau. The west-flowing rivers mostly contribute to the generation of electricity to power Bengaluru’s IT hub and other parts of Karnataka. The Karnataka Power Corporation Limited has 34 dams on its rivers and 24 hydropower stations across the state.
Fisheries also form a substantial means of livelihood, particularly for people who have settled near the river bank. Fishing activities in rivers and their tributaries support the livelihoods of a significant proportion of the population, especially tribals and other local people who are largely dependent on these river systems.
The east-flowing rivers with large drainage area have been the key sources of water for drinking and irrigation. This, consequently led to the building of the initial large dams. With hydroelectricity generation gaining momentum in the last century, several hydroelectric projects came up along the Western Ghats. A series of dams have been built along River Sharavathi, which has reduced the natural flow of the 140-km-long river to a mere 8 km. The ecological impact of dams has been irreparable. For instance, several species of stream fishes are unable to move across the stream for breeding since they are now confined to one side of the dam. Some species are known to move upstream for breeding. But this movement has been restricted now.
A protest by locals against building a dam across River Bedthi in the 1970s resulted in dropping of the project. Subsequently, no large dams were constructed in the state. However, in the past decade, there has been a resurgence of small dams in lieu of large dams. Notable among them is the Yettinahole project, taken up by Karnataka government.
Yettinahole project
Two rivers, Kempuhole and Kumaradhara, originate in Sakleshpur taluk of Hassan district and drain westward through the Western Ghats into the Arabian sea. A massive ongoing project aims to divert nearly 24 tmc of water from the headwaters of River Kempuhole (a tributary of River Netravati) towards the water-scarce regions of Kolar, Ramanagara, parts of Hassan, Tumakuru, Chikkaballapura, Bengaluru Rural, and Devanahalli industrial area.
The project plans to divert the west-flowing Yettinahole stream which eventually joins Kempuhole through eight diversion weirs/dams and a canal network spanning 1,000 km. The water will be pumped from the weirs through giant pipes that cut across the Western Ghats to channel this water eastwards. Seven huge storage reservoirs are also planned to be constructed in other parts of the state. This project, to divert water to the other end of the state, is estimated to cost Rs 13,000 crore. It is an energy- and resource-intensive project and is expected to have an adverse effect on the biodiversity of this region in the Western Ghats. While such projects give weight to support civilisation (through drinking water supply), it is critical that we evaluate the ecological impacts and pursue sustainable alternatives towards meeting our development goals.
The recent floods in Kodagu and Kerala are to be treated as a warning bell for pursuing any alterations to the ecology of the Western Ghats, and rivers in particular. Understanding the river hydrology and floodplains, which form diverse habitats for flora and fauna, can go a long way in arriving at sustainable solutions.
Time and again, ecologists have raised concerns against river linking and the threats it can cause to larger ecosystems. It is crucial that policymakers apply an integrated river water management framework that is evolved at a watershed level. Development goals should be evolved locally, and the water demands should be assessed at watershed levels. Unfortunately, the development activities at Yettinahole appear to be another disaster in the making.
(The writers are with Gubbi Labs,
Bengaluru)