The degradation of riverine ecosystems. resulting from changes in
natural flow regimes. is incrc;1,mgly recognized as hcing amon1-'.Sl the most sig­ nificant negatl\
e effects of hydraulic structures. l;m iron mental 1km, are managed releases from a reservoir
intern.led to mitigate these impacts. Numerous techniques have been developed to estimate
environmental flows but, for a variety of rea­ sons, these methods are rarely applied
in developing countries. The Ethiopian
Government is planning major hydropower and irrigation development in the catch­ ment or the Blue
Nile River. This paper repor1, the 1indings of a first attempt
to rigorously quantify environmental llows in the Blue Nile R1\er. Three desk­ top
hydrological methods, the Global Environmental Flow Calculator. the Desktop Reserve Model. and the
Tennant 1Hethod, were applied at three locations. With reasonable consistency they indicate that
21-28<:.1 of the mean annual flow may he sufficient to sustain basic ecological
functioning. The results. which are low­
,:ontidence estimates. need to he confirmed with much more detailed studies. hut provide a basis
for discussion and (·an contrihut.e ttJ the early phases of planning.