Die nordwaartse begrensing van die duinsee van die sentrale Namib langs die Benede-Kuiseb

Abstract

Abstract provided by author:

If the rate of annual groundwater extraction from the Kuiseb River exceeds the rate of replenishment, the plant and animal life in the area may suffer, but the dunes south of the area between Hudaob and Rooibank will not extend themselves northwards to fill or cross the Kuiseb River. The Namib Sand Sea probably originated in the Late-Cretaceous to Miocene and the consolidated sand was reactivated in the Late-Miocene to Pliocene to form the presently active dune field

In this study, 132 samples of dune sand and 76 samples of sand from the Kuiseb river were analysed by sieving, optical and computer methods. Statistically significant differences regarding median phi, average grain size, sorting, roundness and heavy mineral contents between dune and river sands were obtained, indicating that the present amount of dune sand being shed in the Kuiseb River bed is insignificant. Wind data for four stations in the area was analysed in terms of the geomorphological effectiveness thereof. Wind velocities of 16 km/h and their frequencies were used to calculate average annual and resultant sand transportation vectors, using Bagnold's and Landsberg's formulae. From the interior to Rooibank, resultant sand transport vectors indicate a net annual displacement of sand generally southernly of the Kuiseb River, while the resultant for Walvis Bay is northeast

However, trend surface analysis on the dune sand indicated a northeasterly direction of displacement and on Kuiseb samples a direction along the river's present course. This can be explained in that parameters such as grain size, roundness etc., accentuates the historical direction of transport of sand and not necessarily that of the present. The northeastern displacement of Namib dune sand in the study area is thus a fossil phenomemon. The present frequency and volume of runoff in the Kuiseb River still maintains sand transport downstream as during its geomorphic history