Impact of erosive winds on morphology of sand dunes in Semnan Plain

Sand transport by erodible winds is one of the most important wind processes in arid and semi-arid regions. In this study، in order to determine the wind regime، different indices of same wind aspect index (UD)، sand transport potential index (DP)، erodible winds direction resultant index (RDD)، transport potential resultant index (RDP) were studied and compared with sand dunes morphology index in Semnan Plain. Garmsar، Semnan، Damghan and Biarjomand synoptic stations anemometer data and sand rose graph software were used to analyze wind data، sand transportation potential and sand rose drawing. Results showed that wind sand transportation potential is relatively high at all studied stations and more than 3000 vector unit (VU) throughout the year، according to six m/s threshold velocity which presents highly potential of wind erosion and sand transportation in the region. Annual (UD index is more than 0. 9 in Damghan station and varies between 0. 3 to 0. 8 in other stations. RDD index is also reflecting wind direction changes from 130 to 180 degree. These two indices are representing barchan sand dunes، barchanoid and or silk shape longitudinal dunes in Semnan_Garmsar plain that are formed along north-northwest to south-southeast winds. This condition show the close adaptation with Alborz mountains cold and high pressure condition at the north part of the region and southern situation of Gramsar، Damghan and Semnan plain and also with topography pathway of the region. Sand dunes moving index shows that they are moving and their current vegetal coverage is the result of de-desertification activities.