Luangwa River ago, there was no way out and the Luangwa Rift filled with a Rift Valley Lake called the Madumabisa Lake, which rivalled Lake Malawi in size. The water of the lake overflowed in a river to the south-west, towards what is now the Kalahari, where it combined with the Okavango, Upper Zambezi, Cuando and Kafue rivers, emptying into the Limpopo River and flowing to the Indian Ocean. Several geological events combined to produce the current river systems. Faulting produced another graben just to the south of the Luangwa Rift, and running east-west: the Zambezi Rift Valley and the Chicoa Trough.
Chicago River lowest since 1918. In 2012 Lake Michigan-Huron's seasonal rise was about 4 inches where it usually is about 12 inches. Normally the Chicago River water level is two feet lower than the lake and therefore does not flow into the lake. If the lake level falls too low threatening to reverse the river flow, the Metropolitan Water Reclamation District of Greater Chicago would be forced to close locks between the lake and river for longer periods of time limiting navigation. A reversal flow of the Chicago River into Lake Michigan would have a negative impact on navigation and on the