Mackenzie's idea was to cut a channel from one of the sand-barred lagoons north of Cape Juby, south to a large plain which Arab traders had identified to him as El Djouf.
He proposed that this inland sea, if augmented with a canal, could provide access to the Niger River and the markets and rich resources of West Africa.
But it covers less than 250 km² and is 500 km north of the geographical area identified as El Djouf (also known as the Majabat al-Koubra[5]) which has an average elevation of 320m.
Mackenzie never travelled in this area but had read of other sub-sea level desert basins in present-day Tunisia, Algeria, and Egypt similar to those found near Cape Juby.
Roudaire and de Lesseps proposed that a channel be cut from the Gulf of Gabès in the Mediterranean to the Chott el Fejej[6] which would allow the sea to drain into these basins.
[7] The project was ultimately rejected by the French Government and funding was withdrawn when surveys revealed that many areas were not below sea level as had been believed.
[17] In 1905, engineers working on an irrigation canal in southern California accidentally released the waters of the Colorado River into a formerly dry basin, creating a large saline lake known as the Salton Sea.