Abstract:
The basin is undergoing extensive changes due to agro-ecological, socioeconomic and institutional developments. Livelihoods vary from area to area depending on the physiographic conditions and availability of land and water. Irrigation development has been the major strategy- for livelihood enhancement of the people in the basin// However, tea plantations have replaced the natural vegetation that covered the mountains in the past and abandoned tea lands have been degraded by severe soil erosion. Newly introduced trees like pine and eucalyptus were planted under reforestation programs in the 1950s in this area . They have had a negative impact on the hydrology of the basin, causing some small streams to dry up.// The increasing trend of agro-chemicals usage for irrigated agriculture by the basin farmers is likely to have adverse impacts on the biodiversity of the lagoons. Irrigation development has had negative impacts on the aquatic environment also Specially, large scale deforestation, removal of vegetation cover and encroachment of reservations and other conservative areas with in the basin have drastically reduced watershed performance and environmental friendly behaviors which have severely affected the maximum efficiency of the catchments. An increasing competitive usage of water resources by several sectors can also be seen within this basin An accurate topographical maps to scale 1:50,GOO have been used to digitized the basin and it's sub catchments using geographic Information System(GIS1. Divisional Secretariat Divisions |DSD) falling into the Walawa basinand different types of land usages in the basin were identified using Multi Layer Analysis in GIS - Geoprocessing.// To obtain an average rainfall value over the catch men and sub catchments of Walawa basin, the Thiessen polygon method was used The runoff coefficients for the sub catchments Samanalawewa and Udawaiawaof the basin were calculated from the daily reservoir water balance computations under some assumptions for the period. Irrigation recharge contribution to ground water were also calculated. But, in this study, river recharges were not calculated due to the non-availability of required data. Ground water withdrawal for each seasons were also calculated separately for each zone.// Human, livestock, agio and industrial water consumptions were also calculated under some assumptions from year 2000 lo 2005.Collected the necessary data and information required for the identification of mitigatory measures towards watershed protection to promote soil and water resources conservation within the basin Therefore, the output objectives are directly related to draw our attention lo identify the suitable strategics for the equitable, efficient and effective water resources management and watershed management practices preserving soil, water and other natural resources, reducing waste to a minimum and meeting the water requirement of a given demand site. This will be very useful for the sustainable development of the basin.
