Lower Kuiseb River sediments and their control on dust emission

Previous studies, using remote sensing, have identified the Kuiseb River in Namibia as the dustiest river in Southern Africa. Dust plumes detected from this basin are mostly associated with the Lower Kuiseb River, between the end of the bedrock canyon at Natab and the Kuiseb Delta towards the Atlantic Ocean. The purpose of this study was to examine the surface materials of the Lower Kuiseb River and establish their potential towards dust production, leading to such plumes. This investigation focused predominantly 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, all of which were analysed using a Malvern Mastersizer 2000 laser diffractometer. In addition, other sediment characteristics such as mineralogy, organic matter content, soluble salts; and selected surface roughness elements were also considered. Furthermore MODIS satellite imagery was used to assess the dust emission activity from each of the geomorphological units sampled in the field for the period from 2005 to 2013. This study has demonstrated surface sediments suitable for dust production to increase towards the coast with particular "dusty" floodplain surfaces between Swartbank and Rooibank, as well as the Kuiseb Delta. It appears that silt crusts formed as the flood water dissipate, provide a main source of appropriately sized material for deflation. The crusts consist entirely of silt and clay sized material, with a maximum of 97% <63&#956;m, 39% <10&#956;m and 6% <&#956;m. Dust producing surfaces of the gravel plain include the gravel plain drainage, which has the largest quantity of clay sized material (maximum of 11% <&#956;m). Anthropogenic disturbances of the surface are likely playing a role in the production of dust, with livestock farming causing a fragmentation of crusts in the river valley, and mining and off-road driving disturbing the gravel plain.

Grantor dc:publisher.institution

Department of Environmental and Geographical Science

Year dc:date.issued

2013

Author dc:creator

• Von Holdt, Johanna RC

Advisor dc:contributor.advisor

• Eckardt, Frank

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/11427/12755

OAI identifier oai:identifier

oai:open.uct.ac.za:11427/12755