Technical Note: Peak flow Estimation in Ungauged Catchments Using Flow Index

In regional flood frequency analysis, instead of using the data from a single station, it considers the data and characteristics of a group of similar stations. This study was carried out in Qazvin province and is based on linear momentum that Hosking and Wallis are provided this method as a new approach to flood frequency analysis. The results of factor analysis showed that perimeter, equivalent diameter, time of concentration, length of main waterway and area were the main variables affected flood magnitude. Based on cluster analysis and using the factors affected flood peak, the remaining 15 stations, were divided into two homogenous regions. Homogeneity of these two regions was confirmed using homogeneity test of L-moments. Based on the best-fit criteria of Zdist, GNO distribution is the best fit for the entire region but for one and two homogeneous regions, GLO and GPA distributions were the best fit, respectively. Parameter values for each of the selected distributions were calculated using linear moments and discharges with different return periods were estimated using the best regional distribution for all stations. Finally, after drawing of growth curves, the regression relation between average discharges and watershed areas were obtained at each region. Based on these relationships, at un-gauged locations, peak discharges can be estimated using index flood method for different recurrence interval.