Kształt barchanów jako wskaźnik reżimu wiatru na przykładzie Sahary Zachodniej Maroko

Barchans are characterized by a symmetric shape independently of their stage of development and the axis of symmetry parallels to the dominant wind direction. However, shape of the dunes can be modified by several factors, among which most important are: change of wind regime, dune collisions or interaction of closely spaced dunes, ground surface relief, asymmetric sediment supply. The aim of the study was to analyze the impact of short-term (diurnal) and long-term (seasonal) changes in wind direction and velocity on shape of barchan dunes. The study was conducted in southern Moroccan area of Western Sahara, between Tarfaya and Laâyoune. This area is characterised by significant variability of active wind (RDP/DP=0,66) which is unfavourable for barchans development. Measurements were conducted in two spring seasons of 2011 and 2012 and two autumn seasons of 2007 and 2011. 52 isolated barchans were selected for detailed studies. Based on GPS-RTK measurements, precise 3D models of the landforms were obtained allowing the detailed analysis of dune shapes. Changes of basie morphological parameters were analyzed as well as shape changes occurring the windward slope and within dunes horns. The shapes of the barchans were correlated with the short-term and the long-term wind regime. It was found that basic morphological parameters are not good indicators of wind variability, with the exception of barchan horns lengths which change according to the seasonal wind regime. Short-term wind regime changes are well registered by: i) "collars" developing along the dune crestlines, ii) "tongues" developing at the ends of dune horns and iii) location of the dune apex. On the other hand, beaded horns testify for very strong wind. I was found, that mentioned features develop and undergo modification during first days or even hours of changed wind regime. The analyzes of barchan shapes, performed in different seasons, proved that even a several-month long period of highly diversified wind regime does not change basie shape of the barchans. Therefore, it can be inferred that barchans development does not depend exclusively on wind regime.