تحليل فراواني منطقه اي سيلاب به روش هيبريد در شرق و شمال شرق ايران

Flood Frequency Analysis Using Hybrid Method in Khorasan Province, Iran

In water resources management and flood forecasting, making reliable predictions become crucial. There are many ungauged watersheds in arid and semi-arid regions of Iran that need suitable method to estimate peak discharge. One of the methods for flood frequency analysis in arid and semi-arid regions is Hybrid Method. This study was carried out to evaluate Hybrid Method for estimating peak flows in east and northeast of Iran and compare this method with index flood method. At first, the test regional distribution function (Log Pearson) was fitted and inststaneous peak discharges with different return periods were calculated. Using factor analysis the independent and important variables were determined. These factors include: area, mean elevation, drainage density and annual average rainfall. At the next stage, two regional hydrologic models were obtained and hydrologically homogene areas were determined with cluster analysis of data for Index flood Method. According to Hybrid Method, the classification of groups was taken on the basis of area of each watershed and three homogene regions with various areas were determined. Comparison of Hybrid Method with Index Method in Sheshtaraz station showed that only in return periods higher than 10 years, Index Method gives more accurate results. But in two other stations (Frizi and Shast-dareh), the results Hybrid method in all return periods showed more accuracy comparing to index Method.