structural:reformatting
Delta

The delta of the Zambezi is today about half as broad as it was before the construction of the Kariba and Cahora Bassa dams controlled the seasonal variations in the flow rate of the river. Before the dams were built, seasonal flooding of the Zambezi had quite a different impact on the ecosystems of the delta from today, as it brought nutrient-rich fresh water down to the Indian Ocean coastal wetlands. The lower Zambezi experienced a small flood surge early in the dry season as rain in the Gwembe catchment and north-eastern Zimbabwe rushed through while rain in the upper Zambezi, Kafue, and Lake Malawi basins, and Luangwa to a lesser extent, is held back by swamps and floodplains.

The discharges of these systems contribute to a much larger flood in March or April, with a mean monthly maximum for April of 6,700 m (240,000 cu ft) per second at the delta. The record flood was more than three times as big, 22,500 m (790,000 cu ft) per second being recorded in 1958. By contrast, the discharge at the end of the dry season averaged just 500 m (18,000 cu ft) per second.

In the 1960s and 1970s, the building of dams changed that pattern completely. Downstream, the mean monthly minimum–maximum was 500 to 6,000 m (18,000 to 212,000 cu ft) per second; now it is 1,000 to 3,900 m (35,000 to 138,000 cu ft) per second. Medium-level floods especially, of the kind to which the ecology of the lower Zambezi was adapted, happen less often and have a shorter duration. As with the Itezhi-Tezhi Dam 's deleterious effects on the Kafue Flats, this has these effects: