For hydrologists, time of concentration (TC) is one of the most important parameters to be able to predict the response of a watershed to a given rain event and plays a key role in rainfall-runoff simulation. There are several methods to calculate the TC. The time of concentration is defined as the time from the hydraulically furthermost point to watershed outlet. In this study, we integrated 22 formulas from various references for calculating time of concentration and selected seven formulas by considering the specific conditions and limitations that are suitable for Shafaroud watershed with an area of 345.4 km 2 , located in the western Guilan province of northern Iran. They included Ventura, Passini, Bransby-Williams, Carter, Johnstone-Cross, Izzard and Papadakis-Kazan. The TC values obtained from the mentioned methods were applied in HEC-HMS software for the four rainfall events of June 5, The results indicated that peak flow values obtained by the Bransby-Williams method are most consistent with the observed peak data values and better presents the hydrologic condition of the watershed.
Landslide is one of the most destructive natural hazards that can impose economical and life loss. Fortunately, through numerical and spatial analysis we can lessen the damages caused by landslides. In this study which goes through landslide susceptibility mapping, a combination of AHP and Fuzzy approaches is applied. AHP is used in order to prioritize the effective criteria and Fuzzy method is used in two steps, factor map fuzzification, and factor maps are calculated and overlaid after fuzzification. In order to achieve the best output susceptibility map, 6 scenarios has been proposed in fuzzy overlay step for a study area in Iran as a case study and the best scenario has been chosen according to the comparison of every output with observed landslides layer. The susceptibility map that has the greatest overlap area was the result of using fuzzy Or in overlap step which is considered as a suitable way in hazard risk zonnation. Analysis of the final landslide susceptibility map shows that scenario 6 which is proven to be the most suitable outcome, has the least AUC= 0.3 and matches with observed landslides much better than other scenarios, and through physiographical analysis, we found that most landslides have occurred and are probable in are used as good ranges, are in middle slope angle, and have northern slope aspects.
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