The crescentic sand dune mass known as the 'barchan' occurs extensively on the Kuiseb River delta south of Walvis Bay. The occurrence of these dunes is of sufficient density to present a continuous hazard to the inhabitants of the region. Quantitative measurements were made on a number of the barchans from 1961 and 1976 air photographs to determine the rate of dune advance. This work was in part repeated during a field programme in the delta in January 1988. Dune movement (d) was plotted against height of the dune (h) for the barchans and showed a clear linear relationship of the form d = a + bh. Moreover, the movement of the dunes showed a marked increase in rate of displacement during the 1976-1988 interval, as compared to the 1961-1976 interval. This difference is attributed to variations in the wind conditions, dune height and periodic fluctuations in the sand supply. That the dunes appear to be advancing more rapidly during certain years has wide implications for dune control.