The long term (1915 – 2014) average annual flow at Diem station is about 50 BCM. However, the annual flows of the Blue Nile show strong inter-annual variability. The 1980’s have been particularly dry period. Known years of low flow are: 1978 (annual flow: 26 BCM), 1979 (38 BCM), 1982 (28.8 BCM) and 1984 (29.7 BCM). Years of high flows were: 1961 (63.8 BCM), 1964 (60.9 BCM), 1988 (63 BCM), 1998 (65.9 BCM), and 2014 (63.6 BCM). Due to these high fluctuations in the flow, any meaningful use of the river requires storage dams to regulate the flow and thereby provide reliable water supply.