The Hindu : Vented dams to help in water management

Online edition of India's National Newspaper
Sunday, Sep 22, 2002

Southern States

Southern States - Karnataka

Vented dams to help in water management

By M.Raghuram

MANGALORE SEPT. 21. Harnessing of west-flowing rivers in Uttara Kannada, Udupi, and Dakshina Kannada districts to improve availability of water for drinking and irrigation is one of the ambitious programmes of the State Government in recent years.

The Rs. 145.5-crore project began in a modest way with the construction of a vented dam across the Nethravati. The programme, encompassing a catchment area of 1.29 lakh hectares of arable land in these districts, aims at irrigating 23,931 hectares of land.

When all the 907 vented dams will be ready by the end of the Tenth Plan, 17 taluks in these districts can get water under this programme.

The project harnesses the waters of the rivers originating in the Western Ghats and joining the Arabian Sea after flowing for a distance less than 100 km.

The Kumaradhara, the Nethravati, the Shambhavi, the Payaswini, the Gurupur, and nearly 40 of their tributaries flow westward in Dakshina Kannada. The Varahi, the Chakra, the Seeta, the Swarna, the Kollur, the Udyavara, the Shambhavi, and the Pangala in Udupi District, and the Kali, the Gangavali, the Aghanashini, the Badagane, the Sharavathi, and the Venkatapura in Uttara Kannada flow westward. The project hopes to harness the waters of these rivers through a network of vented dams.

The vented dams will be constructed to hold maximum water. Since they will be built in a series, each of them will be complementary to the other situated downstream. The project aims at raising the groundwater level considerably making the catchment area of each dam a huge watershed.

A network of west-flowing rivers drains the district with outlets to the Arabian Sea through estuaries.

The Central Water Commission (CWC) and the Water Resource Development Organisation (WRDO) operate thirteen river gauging stations at six rivers. The estimated average annual flow of the district's rivers is to the tune of 29,561 million cubic meters (mcm) per year. The Nethravathi with a catchment area of 3357 sq. km. contributes 12,434 mcm. a year followed by the Gurpur with 2915 mcm. a year, the Pavanje with 619 mcm., the Mulky with 1253 mcm., the Swarna with 1889 mcm., the Sita with 2738 mcm., the Varahi with 2051 mcm., the Chakra with 1061 mcm., and others contribute 4601 mcm. a year. The district has a total catchment area of 8,326 sq. km.

While the rivers frequently overflow during monsoon, they often experience periods of no flow from December to May. The data available with the CWC on the quality of rivers speaks about apparent pollution in the river, especially Gurupur, which flows adjacent to Mangalore city.

The total surface water consumption is estimated at 759 mcm. a year, which is 60 per cent of the total consumption. Irrigation accounts for 95 per cent. The present total consumption only amounts to 2.5 per cent of the total river flow.

Demand for surface water has risen considerably with the industrialisation of the city. Innovative methods of water harvesting and conservation have improved the water availability for domestic and industrial applications. The problem areas in the management of surface water are the pollution sources in Dakshina Kannada.

A study by the Mangalore City Corporation states that the water quality problems will probably be compounded by lack of available river water during the dry months when the surface supplies are overexploited and saline waters ingress upstream and threaten fresh water resources.

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