Climatic Data and Satellite Imagery for Assessing the Aeolian Sand Deposit and Barchan Migration, As a Major Risk Sources in the Region of In-Salah (central Algerian Sahara)

Climatic data from the In-Salah weather station covering the period 2005–2014 and bi-date satellite imagery have been used to investigate sand drift potential and barchan migration in the Erg Sidi Moussa dunefield. The application of the Fryberger and Dean’s (1979) model on surface wind records revealed that the studied area belongs to high-energy wind environments (drift potential (DP) = 785 VU) with strong spring (May, April) and summer (July, August) moving-sand seasons. The net drift potential RDP was about 560 VU, which is the equivalent of 39 m3 of transported sand across 1 m land width per year. The values of resultant drift direction (RDD) were fully ranged between 50 and 76° with an average of 64°; this signifies that the prevailing winds and consequently sand transport are directed toward the west-southwest sectors. Beside, significant value of the directional variability index RDP/DP was detected (0.71), confirming the low effective wind variability and its directional steadiness throughout the year. Wind regime in the Erg Sidi Moussa was recognized as wide unimodal, and fully associated with crescent-shaped sand dunes including transverse dune, barchanoid ridge, and individual barchan. Climatic data for the In-Salah airport station have been used to estimate the dune mobility index M according to Lancaster (1988); results showed that the M values were largely superior to 200, implying that barchans were fully active during the considered period. The accurate measurement of the barchan migration rate and direction had been realized, by applying the point to point geo-correlation technique on 29 individual barchans; basing on bi-temporal fine resolution imagery (2002 and 2013), results showed that the barchan movement distance were ranged between 7 and 18 m/year (12 m/year average), and that the barchan displacement rate was—in general—inversely proportional to their size, namely the height ranging from 5 to 24 m and the width which ranges from 50 to 335 m. Further, the barchan displacement angle was about 63° average, in well accordance with the calculated resultant drift direction RDD (64°). Consequently, urban areas, agricultural reclamations, and socioeconomic installations downwind are seriously facing the risk of encroaching sands and migrating barchans.