The effect of the geographical direction on alluvial fans dimensions (Case study: Shirkouh-Yazd)

Alluvial fans are one of the most important of types of geomorphic landforms in mountainous regions, especially in dry and semi-dry region, which flow processes create them with reducing the slope and opening the valley after leaving the mountain.This study investigate the effects of geographic directions on the dimensions of alluvial fans in down streams in Shirkouh Mountain in the central part of Iran's plateau with dry climate. . This mountain is limited to the mountains Boohrook and Dasht-e- Fakhrabad from the east, Tang Chenar and Turanposht from the south, Farashah and Taft city in the west, and with a short distance to Yazd city in the north. It is determines about 24 alluvial fans in the different slopes of the Mountain. After determining the landforms, four geometric characteristics of them includes fans area and length, fans width in the center and in the base were calculated in different slope with different orientations using GIS. Then, using the same software, geometric characteristics of the watersheds include area, environment, average height, average slope, basin length, gravilious coefficient, basin shape coefficient, and drainage density of basin were measured in four directions of geography. Then, using SPSS software, the correlation and also the regression between geometric parameters of the alluvial fans and geometric factors of their upstream basins was calculated. Analyzing showed that geometric factors of the basins in eastern slopes with northern direction and also in northern slopes has been less affected on the fans dimensions. But on the eastern slopes with southern directions and western slopes as well, whose basins are higher and exposed to moist masses, Geometric characteristics of catchment are the most important parameters affecting and controlling the dimensions of fans.