1.1.1.WATER RESOURCES Sri Lanka’s radial network of rivers begins in the central highlands. There are about 103 distinct river basins covering 90 per cent of the country. The southwest quarter of the island has seven major basins with catchment areas ranging from 620 to 2,700km². They are: Kelani ganga (2,292km²), Kalu ganga (2,719km²), Maha oya (1,528km²), Attanagalla oya (736km²), Gin ganga (932km²), Nilwala ganga (971km²) and Bentota ganga (629km²). An exception to the radial pattern is the largest basin, that of the 335km-long Mahaweli River, which has a catchment area of 10,448km². After leaving the central highlands, it runs north for 90km from Minipe to Manampitiya and then a further 70km through several distributaries as far as Verugal and Mutur on the east coast. Most Sri Lankan river basins are small; only 17 of the 103 basins exceed 1,000km². In addition to the Mahaweli basin, four others are larger than 2,500km². Three of these (Deduru oya, Kala oya and Malwatu oya) have their entire catchment area in the dry zone. Only Kalu ganga is in the wet zone. Total runoff in Sri Lanka is estimated at 49.2 km3/yr. Groundwater resources have been extensively used since ancient times for domestic purposes using shallow open wells in almost all parts of the country. Sri Lanka’s largest aquifer extends over 200km in the northwestern and northern coastal areas. There are about 15,000 tube-wells in the country. The quality of the groundwater is generally fairly good and relatively constant throughout the year. However, in some parts of the country (northern and northwestern coastal areas) excessive concentrations of iron and nitrates (due to agrochemicals and fertilizers) have been reported. Furthermore, due to uncontrolled abstraction of groundwater for domestic and agricultural uses, brackish water intrusion has occurred in the coastal areas. In 1985, estimated internal renewable groundwater resources were 7.8km3, most (around 7km3/yr) returning to the river systems and being included in the surface water resources estimate. In 1991, the total internal renewable water resources of the country were estimated at 50km³/yr. Economic development, population pressure and growing demand for food production, electric power and adequate water and sanitation services are placing increasing pressure on water resources. The demand for water has outstripped supply, particularly in the country’s dry zone, where most irrigation schemes are located. In 1996, total dam capacity in Sri Lanka was 5.942km3. Dams in Sri Lanka are classed according to the materials they use. They are mainly earthen, rockfill or concrete dams. Earthen dams are the most common type, the longest being the Parakrama Samudraya Dam, which is 13.5km long with a storage capacity of 0.12km3. The highest in this category is the Senanayake Samudraya Dam at 44m, with a storage capacity of 0.95km3. The Victoria dam, built under the Mahaweli multipurpose project, is the highest concrete (double curvature) dam, with a height of 106m and storage capacity of 0.73km3. The gross theoretical hydropower potential in Sri Lanka is estimated at 8,000 GWh/yr. In 1997, 16 hydropower plants were in operation with an installed capacity of 1,103MW. Hydropower accounted for 81 per cent of electricity generation in Sri Lanka.

1.1.2.WATER USE Large-scale development of water resources for irrigation and hydropower has progressed rapidly over the last 50 years. In Sri Lanka, the quantities of water required for industrial and domestic uses are low compared to irrigation and hydropower. In 1990, water withdrawal for agricultural activities was estimated at 9.38km3. The corresponding values for domestic and industrial activities were 0.195km3 each. Groundwater is an important source of water for irrigation and domestic use. It is increasingly used as drinking water, especially in small towns and rural areas. The total estimated water demand for 2000 was 10.92km3. Of this, 90 per cent was for agriculture, 7 per cent for domestic purposes and 3 per cent for industry. Supply of drinkable water to communities is in the early stages of development. In 1992, 53 per cent of the population (87 per cent of the urban and 49 per cent of the rural population) had access to safe drinking water. Other people used unprotected wells, rivers and tanks. High incidences of water-illnesses (120,000 recorded hospitalizations per year for diarrhoea) indicate that there is a serious water quality problem. The government has given high priority to providing water supply to urban communities where groundwater is contaminated. The government spends about US$45 million/yr to provide the population with piped water. Sri Lanka’s only public sewer system is in Colombo. It serves about 20 per cent of the Colombo metropolitan region and the collection is not treated. Very few industries have treatment plants while others discharge straight into waterways.

1.2.WATER QUALITY, ECOSYSTEMS AND HUMAN HEALTH Major environmental problems in Sri Lanka include: deforestation; soil erosion; wildlife populations threatened by poaching and urbanization; coastal degradation from mining activities and increased pollution; freshwater resources being polluted by industrial wastes and sewage runoff; waste disposal; and air pollution in Colombo.