The research about effective process on the Anabraching formation in Mahabad River

Mahabad River is located in south part of Urmia Lake. The River is deformed to Anabranching in the region between the upstream of Mahabad dam and downstream of detour dam. The aim of this research is evaluation of the factors that affects the formation of this kind of channel. For this purpose, multiple physical variables including wide bed, stream power, channel slope and the amount of the bank clays were studied. The form of channel were assessed at two different times before and after build of the dam based on 1346 and 1382 aerial photographs. The aerial photographs scanned and processed in Geographic Information System, in order to extract of the wide channel. Finally, the effect of the dam on river and changes after the construction of the dam were determined. The results showed that increasing recent period’s runoff potential and basin erosion were provided the necessary potential for Anabranching formation in this area. But, the most important factor for construction the Anabranching was the dam building causes decreasing peak flow and increasing bed-material deposing rate. The river adjusted by deformation in response to deposition of bed-materials as a result of decreasing stream power. On the other hand, decreasing island length and nonoccurrence of Anabranching channel to Nanson and Knighton model was the result of the presence of the detour dam on downstream.