Ecology of Mahadayi River basin

Ecology of Mahadayi River basin: An overview
By Dr. Nandkumar Kamat

IT was late Pleistocene. The ancestors of modern Homo sapiens were descending south of the Vindhyas. Many followed the river valleys-Godavari, Krishna, Bhima. A few travelled down the resource rich Ghattprabha and Malprabha rivers. From there it was the call of the Arabian Sea and the search for sea-salt which brought these ancient humans to the valleys of Mandovi and Zuari.
About hundred thousand years ago, the nomadic humans entered Goa and dispersed along the trails linking the river banks to the plateaus and the coast. The prehistory of Goa is intimately linked to the ecological history of rivers. At no point of time in their thousand hundred years history, the Goans thought that they would be deprived of the sacred waters of their life line river Mandovi. But the inevitable is likely to happen. The next two weeks would be crucial for the ecological destiny of Goa.
Although Karnataka is a friendly state, its government is allegedly hell-bent to proceed with its plan to build dams on the Kalsa and Bhanduri tributaries feeding the Mahadayi river despite consistent objections from Goa since 1985. The aim is unauthorised inter basin transfer of water from Mahadayi basin to Malaprabha basin. Mahadayi river becomes Mandovi river past Ganjem village in Goa. The ecology of Mahadayi basin is already very fragile on account of massive deforestation and quarrying in Khanapur district of Karnataka. The basin falls in the Western Ghats -a hot spot of megabiodiversity.

The Bhimgarh-Krishnapur limestone caves on Goa-Karnataka border is the only shelter in the world for the rare Wroughton's free tailed bats. The Mahadayi river basin supports hitherto unexplored flora and fauna. For Goa, the freshwater flows from the catchment in Karnataka are essential for maintaining the delicate balance between the saline estuarine zone-from Aguada to Ganjem and the freshwater zone beyond Ganjem.
The Mandovi is an interstate river basin draining area in Karnataka, Maharashtra and Goa. The Basin (1,580 sqkm drainage area in Goa) occupies 42.70 per cent of the total area of the state. The river rises in Jambotighat, about 10 km north-east of Sonasagar in Khanapur taluka, Belgaum, Karnataka at an elevation of about 940 meters above Sea level. The basin lies between latitudes 15 degree 15'24” N and 15 degree 42'00” N and Longitudes 73 degree 45'46” E and 74 degree 24'54” E. The total length of the main river is 87 km, out of which initial 35 km is in Karnataka and the balance 52 km in Goa.
The Mahadayi river in Karnataka is joined by three important tributaries namely the Bail Nadi, the Kotni Nadi and the Bhandura. There are five important tributaries forming the Mahadayi/Mandovi river in Goa portion, namely Surla (or Nanode Nadi), the Ragda, the Dicholi, the Mapuca and the Khandepar (or the Dudhsagar). The Mahadayi / Madei / Mandovi drains a total area of 2,032 sqkm of which initial 375 sqkm in East and North East and South East in Karnataka, 77 sqkm in North East portion of the basin in Maharashtra and the balance 1,580 sqkm in Goa. The basin receives 3,000-5,000 mm rainfall during the monsoon periods extending from June to November. There are 17 rain gauge stations in and around the basin. The stations inside Karnataka are Supa, Khanapur, Kankumbi, Jamagaon, Amgaon and Castlerock. In Maharashtra there is one at Tilariwadi, whereas Goa has stations at Panaji, Sanguem, Margao, Quepem, Mapusa, Bicholim, Valpoi, Ponda, Colem and Marmugao.
The Karnataka government claims that Goa is “criminally wasting'' the Mahadayi water resources. On the contrary, Goa was constantly assessing its ecological needs and the feasibility of constructing small dams and also designs of mini-hydel projects. Goa did not want to pay the heavy price of deforestation and ecological damage which Karnataka government had paid for constructing dams on western flowing rivers such as Kali and Sharavathi. Goa had planned the Mandovi Irrigation Project in the 70s at Nanode village in Sattari taluka. It was supposed to bring under irrigation a command area of 5,902 ha with an annual irrigation of 13,110 ha of land in Sattari and Bicholim talukas. The project was cleared by the Central Water Commission and the Planning Commission. But the ministry of forests and environment did not give the clearance under the Forest (Conservation) Act 1980 probably because it had apprehensions about the submergence of a large, rich forest area under the reservoir. The ecology of Mahadayi basin is very delicate. Karanatka government feels that diverting 7.56 TMC of water would not make a big difference to Goa. This is not true. The freshwater flow from Mahadayi maintains Mandovi. A simple definition of an estuary is an extension of the arm of the sea. What would happen if the freshwater flow is reduced? For some time no changes would be instantaneously noticed. But as time passes, the estuarine front would move deeper, past Ganjem and it could also affect the Zuari basin through the linking Cumbharjua canal. What would be the impact of the advancing salinity front? There would be a drastic change in the ecology, the flora and fauna of Mahadayi/Mandovi basin. If large part of the 52 km long stretch of Mandovi river is rendered saline then the freshwater availability in Goa would be reduced.
The central government, the Planning Commission and funding agencies like the World Bank need to appreciate that unlike the government of Karnataka, Goa is not in a tearing hurry to sacrifice the fragile ecology of the rivers to support large dams. Mahadayi catchment in Karnataka must be left undisturbed. The future of Goa's ecology depends on it. Karnataka government must pay more attention to demand side management, rainwater harvesting, controlled irrigation and better reservoir management instead of arm twisting a small lower riparian state like Goa anxious to conserve its fragile ecology at any cost. Goa has the capacity and is determined to harvest its water resources judiciously.