Analyzing hazard severity of alluvial fans located south Binalud based on acceptability of morphotectonic indices

Alluvial fans are depositional landforms formed where a confined feeder channel emerges from a drainage basin, i.e. between a mountain range and a plain. An alluvial fan is a fan- or cone-shaped deposit of sediment crossed and built up by streams. If a fan is built up by debris flows it is properly called a debris cone or colluvial fan. These flows come from a single point source at the apex of the fan, and over time move to occupy many positions on the fan surface. Fans are typically found where a canyon draining from mountainous terrain emerges out onto a flatter plain, and especially along fault-bounded mountain fronts.Alluvial fans are gently sloping, cone-to fan-shaped landforms created over thousands to millions of years by deposition of eroded sediment at the base of mountain ranges. They are easily recognized in arid, to semi-arid environments such as that of the bajada of southern Binalud. A convergence of neighboring alluvial fans into a single apron of deposits against a slope is called a bajada, or compound alluvial fan. The term active refers to that portion of an alluvial fan where deposition, erosion, and unstable flow paths are possible. If flooding and deposition have occurred on a part of an alluvial fan in the past 100 years, that part of the fan can be considered active. This conclusion can be supported by historic records, photographs, aerial photography, and engineering and geomorphic information. The main objective of this paper is to study the relationship between morphotectonic properties and alluvial fans hazard severity in the alluvial fans located southern Binalud, in order to understand vulnerability of settlements established in these fans. Alluvial fans can be a source of major hazards. Recognizing the type of depositional process (e.g. debris flows, rock avalanches, and sheet floods) in the early stage of urban planning and land development will prevent loss of lives and damage to infrastructure. According to the correlation between active tectonic and hazard severity, has been analyzed urban vulnerability of alluvial fans. In this article to analyze urban vulnerability and hazard severity classification of alluvial fans, in the first step, based on four morphotectonic indices including Vf, AF, Smf and fan conically index, tectonic degree of each alluvial fan was determined. Then, using acceptability index and central weight vector, was measured utility of each morphotectonic index considering weight vector and effectiveness on urban vulnerability. The rank acceptability index describes the share of parameter values granting alternative xi rank r.The most acceptable (best) alternatives are those with high acceptability for the best (smallest) ranks.The central weight vector is defined as the expected center of gravity of the favorable weight space.The confidence factor is defined as the probability for an alternative to be the preferred one with the preferences expressed by its central weight vector.Ultimately three hazard classes were identified for alluvial fan risk. Results indicated that three alluvial fans involving Bozmehran 1, Kharv and Darroud have been gained most acceptability for first rank. Results showed that Vf and Smf are main morphotectonic indices to high acceptability for Kharv and Darroud. This status in the Bozmehran1 was equal for all approximately. The vulnerability classification showed that alluvial fan of Bozmehran 1 has high severity and then population of this region is in face of geomorphological hazards. Also this condition is true for Bozmehran 2.The acceptability analysis for Nishabur city as main settlement established in alluvial fan is different. The result showed that Nishabur obtained moderate vulnerability class which refers to ratio of alluvial fan shape in this area. In spite of active tectonic for AF and Vf, shape ratio 1 for this alluvial fan decline the effects of other tectonic indices. In general landslide and flooding according to the faults and climate conditions in Binalud is probable and possible. So a risk management is needed to mange urban developed on alluvial fan located Binalud. Alluvial fans are flat to gently-sloping masses of loose rock material (largely sand and gravel) that are shaped like an open fan. They form at the base of mountains where fast-flowing streams meet relatively-flat surfaces of basin floors or broad valleys. In this article, has been analyzed correlation between tectonic condition and hazard potential in alluvial fans located south Binalud using acceptability index. Results showed that urban of Bozmehran, Kharv and Darroud are high vulnerable to hazard.