Abstract: Assessing irrigation performance plays an important role in improving irrigation efficiency and water resource management in the low land of Vu Gia – Thu Bon river basin where traditional irrigation practices are applied to a predominantly paddy rice cultivation. Relative Water Supply (RWS) and Relative Irrigation Supply (RIS) were selected as relevant indicators to assess the relationship between water supply and water demand of the irrigation system. About 120 primary and secondary pumping stations were visited during field trips. 13 large primary pumping stations were chosen to validate the actual irrigation supply. Annually there are two crops Winter-Spring and Summer-Autumn being cultivated in this region. Monthly RWS and RIS were calculated for 13 irrigation management schemes during the two crops in the years 2004 - 2005. The obtained results differ from scheme to scheme and were analysed individually. The result presents an under - irrigation supply at six irrigation management schemes including Tu Phu, Tu Cau, Xuyen Dong, Bich Bac, An Trach, Ai Nghia in both crop seasons Winter – Spring and Summer – Autumn, especially from February to July. Both RWS and RIS are high in December and August implying that there is considerable potential to save and use water more effectively during this period. At Ai Nghia and Chau Son irrigation management schemes, RIS values are zero while RWS is relatively high in May demonstrating that rainfall variability plays an important role in changing RWS and RIS. Reducing the irrigation supply should be considered for those periods, so that effective irrigation management can be achieved.
Keywords: water management, water demand, water supply, irrigation performance, relative water supply (rws), relative irrigation supply (ris)