Effect of catchment’s area, slope, and main stream length on the roundness, surface texture, and microcrack of natural aggregates of alluvial fans of Direh Plain

Morphometric parameters of catchments such as area, slope and main stream length can affect some physical characteristics of aggregates including roundness, surface texture, and micro-cracks. In this study,12 alluvial fans with similar catchment lithology were selected based on satellite images, geological maps and field works. In mid part of each fan,150 samples from 3 different sizes of gravel (50 samples for each size) were collected and the above mentioned characteristics were measured. Results show that roundness increases, surface texture soothes and micro-crack decreases with decreasing in slope and increase in area and main stream length of catchments. The lowest rate of roundness belongs to alluvial fans having catchments areas of 33 and 27 hectares and to smallest aggregates (12.5-16 mm), whereas, the highest value of roundness is related to alluvial fans with largest catchments (309 and 206 hectares) and aggregates (37.5-25 mm). In terms of surface texture, the highest crenulation is related to alluvial fans with catchment of 25 hectares and to aggregates size of 16-12.5 mm, whereas the lowest crenulation belongs to alluvial fans with largest catchments (309 hectare) and largest aggregates (37.5-25 mm). In terms of micro-cracks, the lowest percent of cracks (10%) is related to smallest aggregates, and alluvial fans with largest catchment. While the highest percent of cracks (32%) is observed in largest aggregates and in alluvial fans with catchments having areas of 29 and 33 hectares. The main stream length effect on the aggregates characteristics is similar to the effect of catchment area.