The river Atbara rift is formed of two main basins the Atbara and the Gash Delta basin separated by a ridge. The Atbara is a longitudinal basin extending 180 km in a NW4SE direction and 704100 kms wide. The triangular shaped Gash delta basin is 600 km² in area.
Two main rivers supplied sediment to the basins; the River Atbara and the River Gash flowing from north western parts of the Abyssinian plateau. They are both seasonal streams, having their annual floods during the rainy season from June to September. The sediment load of the river Atbara was estimated to be about 14 m.t annually . After the sediments filled the Atbara graben, the flow started moving northward to Egypt. The alluvium varies in thickness from 50 to 200 meters, comprising gravels, sands and clays with the arenaceous materials forming more than 50 percent. The sedimentary column indicates high energy deposition by the Atbara at its initial stages. The sediments that fill the Gash delta are mainly alluvial deposits ranging in thickness from 50 to 100 m. They are intercalated beds of unconsolidated coarse to fine grained gravel, silts and clay with the fine materials, silt and clay, increasing downstream.
