Dust activity and surface sediment characteristics of the dustiest river in southern Africa: the Kuiseb River, Central Namib

Abstract

Previous remote sensing studies (2005–2008) have identified Namibia’s Kuiseb as the dustiest river in southern Africa. The purpose of this study was to extend the dust event record through to 2014, and to examine the nature of the surfaces from which this satellite imagery indicates these dust plumes originate. The new 10-year record confirms the delta as the dustiest geomorphological unit (54% of plumes), followed by the gravel plain (28%) and then the river (8%). No dust originated from the Namib Sand Sea dunes or interdunes. Field observations provided detail about the geomorphological and sedimentological setting of the landscape components. The laboratory analysis focused on the size characteristics of 153 surface sediment samples collected from the Kuiseb main channel, its terraces, delta, gravel plain surfaces and tributaries, dunes and interdune. This study has identified that surface sediments suitable for dust production increase towards the coast with particular ‘dusty’ floodplain surfaces between Swartbank and Rooibank and the Kuiseb delta. We suggest that silt crusts formed as the flood water dissipate, provide a main source of potentially entrainable material for emission. The crusts consist entirely of silt- and clay-sized materials, with a maximum of 97% <63 μm, 39% <10 μm and 6% <2 μm. Anthropogenic disturbances of the surfaces are potentially playing a role in the production of dust, with the area undergoing significant development.