Water for people.pdf - WHO Thailand Digital Repository

4 1 8 / P I L O T C A S E S T U D I E S : A F O C U S O N R E A L - W O R L D E X A M P L E SRuhuna Basins, Sri LankaTHE RUHUNA BASINS IN SOUTHERN SRI LANKA will face major changesover the next two decades. Ambitious development plans indicate thatthe dominant role now played by agriculture is geared to switch to muchmore industrial and service-oriented activities. Obviously, these changes willhave an enormous impact on society as well as on natural resources andrequire the inclusion of issues of water management. Currently, almost allwater resources that are diverted are used for irrigation with only a smallpercent used for industry and drinking water. Most recent development plansshow that the use of water for urban areas and industry will increase from lessthan 10 million cubic metres (Mm 3 ) currently to 100–150 Mm 3 by the year 2025.General ContextMap 18.1: Locator mapI N D I ASRI LANKAC H I N ATHAILANDRuhunabasinsIndian OceanMYANMARMALAYSIASouthChina SeaINDONESIASource: Prepared for the World Water Assessment Programme(WWAP) by AFDEC, 2002.Already today, the Ruhuna basins are important in the broader SriLanka context: they are the location of a major hydropower plant,and irrigation schemes that make a significant contribution to foodproduction and important nature reserves. However, even before theenvisaged development plans are implemented, the basins arealready experiencing major water resource problems, clearlydemonstrated by the recent drought leading to reduced water forirrigated agriculture, insufficient supply of domestic water andnationwide power cuts for up to eight hours a day.The Ruhuna basins area includes three main rivers and severalsmaller basins, and forms part of the hydrologic system of theancient kingdom of Ruhuna.Sri Lanka has a surface area of 65,500 square kilometres (km 2 )and a population of 19 million inhabitants. It is renowned for itshydraulic civilization in which natural resources have been managedover thousands of years. The country has a mean annual rainfall ofabout 1,900 millimetres (mm) but this ranges from below 900 mmin the driest parts of the dry zone to over 5,000 mm in the centralhills. There are 103 distinct river basins in the island, ranging in sizefrom 9 km 2 to 10,450 km 2 . The Ruhuna basins cover 8 percent of theSri Lanka landmass.Major physical characteristicsGeographyThe Ruhuna basins are mountainous and relatively wet. Severalcatchment areas are poorly developed, but there are downstreamflat areas with developed water resources. These lowlands consist ofrolling plains dotted with a few isolated hills. The rivers originatefrom the southern slopes of the central highland massif atelevations of up to 2,000 metres. A large part of the basins is madeup of many types of composed rock, such as granite, migmatite andquartzites (Panabokke et al., 2002).ClimateThe only source of water is rainfall. Monsoonal rains, which fall fromNovember through March and May through September, contribute amajor part of the annual rainfall, which is supplemented by intermonsoonalrains. The mean annual rainfall for the basin is1,574 mm, the depth of which decreases from the upper to lowerreaches and from west to east. The recent rainfall records atselected stations show a trend of decreasing annual rainfall since1970. The decrease is not uniform or highly significant in statisticalterms. The ambient temperatures in the lowlands range from 25 to28 o C, and in the upper elevations from 23 to 25 o C.Table 18.1: Hydrological characteristics of the Ruhuna basinsSurface area of the basin 5,578 km 2Annual precipitation1,574 mm/yearAnnual runoff 78 m 3 /sAnnual potential evapotranspiration1,700 mm/yearUpper catchment1,458 mm/yearLower catchment1,914 mm/yearMajor socio-economic characteristicsThe Ruhunu basins include parts of the Ratnapura, Badulla, Moneragalaand Hambantota districts with population densities of 307, 291, 71 and217 inhabitants/km 2 , respectively. The total population in the basins isapproximately 1.1 million (Jayatillake, 2002b).The average monthly income per household in the Badulladistrict is the lowest in the country. For the year 2000 the nationalaverage Gross Domestic Product (GDP) per capita was US$850, butfor the Ruhuna basins, per capita GDP is estimated at about