Use of radar data to delineate palaeodrainage leading to the Kufra Oasis in the eastern Sahara

Radar-revealed palaeodrainage systems are analyzed using Radarsat-1 data covering the Kufra Oasis and parts of southeastern Libya and northern Chad. The analysis shows that two mega fluvial systems exist to the south of the Kufra Oasis. Along the western one, a mappable polygonal fluvial unit covers 13,628 km2 in area, with the entire watershed extending north beyond the borders of the present 347,160 km2 study area. The eastern system covers 4321 km2 in area and is morphologically similar to the Amazon’s Rio Negro, although the African channel is four times wider. The enormity of these features provides some explanation as to why continuous extraction of groundwater in the oasis and nearby circular irrigation farms is possible. Clearly, these mega fluvial systems formed at some time in the past when rain was plentiful over a protracted time period.