We understand from the passage that, in general, rivers leading to waterfalls

The geological formation of the Victoria Falls of the Zambezi River makes it one of the world's
most unusual cataracts, the term for a giant waterfall. Situated between Zambia and Zimbabwe, it
spreads over a mile in width. Unlike most rivers approaching a cataract, the Zambezi has no
rapids to warn the river traveller of the approaching precipice. A shallow, broad river the
Zambezi continues to move slowly up to the brink of the falls. Then it spills abruptly over the
355-foot precipice with a thunderous roar.