Abstract
The term water use can be classified into consumptive use and non-consumptive use. In Sri Lanka, the highest volume of water is used for irrigated agriculture for paddy cultivation and hydropower generation. In hydropower generation the total amount of water does not undergo a state change i.e. non-consumptive use, whereas in irrigated agriculture only a portion of the released water undergoes a state change i.e. consumptive use. By nature, the balance portion is used for the sustainability ofthe environment including social life. There was no reliable technique to quantify the consumptive use of water in irrigated agriculture. Therefore ,as a common practice the total amount of water released has been accountedfor the event of crop production. If irrigation water is not released for a season, the affected outcome is the immediate loss of crop production. If this is continued for consecutive seasons, several unfavorable situations related to the social life and the environment could be experienced. Hence, one has to identify the different water use activities related to irrigated agriculture and apportion the released amount of water among such activities. Techniques cf Satellite Remote Sensing can now be used to estimate the consumptive use of water irrespective ofthe type of vegetation cover over the land surface. This paper describes the authors work of estimation ofthe amount of water consumed by the paddy crop at the Kaltota Irrigation Scheme using Geoinformatics techniques. The economic benefit of water for paddy production is compared with the same for hydropower generation at Samanalawewa Hydropower Station which is situated on the same water course at the upstream of the Kaltota Irrigation Scheme.