The Augrabies Falls Region: A Fluvial Landscape Divided in Flow but Magnificent in Spectacle

Abstract

The fluvial landscape of the arid Augrabies Falls region is characterised by a complex of channels, waterfalls and gorges eroded in granitoid bedrock. Anabranches of the Orange River divide and rejoin around stable, predominantlybedrock islands, and many terminate at or near the permanently flowing 50–60 m high Main Falls, with the largest summer floods also activating other normally dry waterfalls. Below the Main Falls, a single channel flows within a deep, narrow gorge up to ~18 km long. A developmental model is outlined, which posits that waterfall retreat and concomitant gorge formation in the initially low-relief valley floor has initiated a wave of erosion that represents a renewed phase oflandscape denudation. The faster retreat of the Main Falls is driving changes to upstream flow patterns. Over a long time scale, incision along anabranches that are tributary to the gorge will combine with gorge sidewall retreat, thereby leading to valley floor dissection.