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The Eastern Sahara is presently the driest place on Earth. However, there is geographical, geological, and archaeological evidence of wetter climates in the past. Its dune fields are largely enclosed in topographic depressions that served as terminal points for a number of palaeo-rivers and streams. In some of these channels, moisture from occasional rainfall, or from leaking fractures tapping deeper confined aquifers, has been detected at 25 cm beneath the surface. Radar images are used here to map the distribution and morphology of the channels North of the Gilf Kebir plateau and beneath the Great Selima Sand Sheet. Radar waves have the unique ability to penetrate up to 2 m beneath dry, fine-grained desert sand to reveal subsurface features. It is believed that fluvial episodes in the Eastern Sahara are closely linked to the vast accumulations of sand, including: a) the Great Sand Sea, where major channels lead from the Gilf Kebir plateau Northward toward lower topography; and b) the Great Selima Sand Sheet, where four major drainage lines cross it or lead to its borders. The convergence of the channels suggests that surface water occupied inland depressions. Some of that water would have seeped into the underlying porous sandstone to accumulate as ground water beneath both the Great Sand Sea and the Great Selima Sand Sheet.