Annual flow is above 5,000 Mm3 on average, but varies substantially both within and across years, and includes two flood seasons each year. Between 1944 and 1978, average total flow (at Garissa) was 6,105 Mm3, varying from only 1,789 Mm3 in 1949 to 13,342 Mm3 in 1968. During the 1982-1996 period, annual flow remained above 5,000 Mm3 as well. A series of hydroelectric dams have been constructed along the river, including the Kindaruma Dam in 1968, the Kamburu Dam in 1975, the Gitaru Dam in 1978, the Masinga Dam in 1981, and the Kiambere Dam in 1988. A 2003 study reported that two-thirds of Kenya's electrical needs were supplied by the series of dams along the Tana River.
^ abNakaegawa T., Wachana C. and KAKUSHIN Team-3 Modeling Group. (2012). "First impact assessment of hydrological cycle in the Tana River Basin, Kenya, under a changing climate in the late 21st Century," Hydrological Research Letters, 6, pp. 29-34.