Assessing the hydrologic homogeneous regions and regional distribution functions with linear moments method in Golestan Province

One of the factors that are required in the regional analysis is obtaining hydraulic homogenous regions and assessing the appropriate statistical distribution function in each homogeneous region. In this study, the methods of linear moments and Cluster analysis in SPSS were used for making homogeneous groups. And to select the good distribution, HAYFA was used to determine the best regional distribution by low flow. 29 hydrometric stations with appropriate long duration and uniform distribution in Golestan province were selected. The minimum duration of daily flow records was 11 years for Nomel station and the maximum duration of 44 years was for Galish station. After sorting the daily flow the number of courses was characterized with low flow and also the maximum days number with low flow was determined. The method of linear moment and cluster analysis in SPSS, was used to assess homogeneous regions. The study area is divided to 4 regional homogeneous categories based on maximum days with low flow. Using both homogeneous Hosking and Wallis statistic method, there is no awkward station and region is quite homogeneous. Finally, using the index z and executive file in FORTRAN, the best regional distribution function for different extracted homogeneous groups was determined. Based on maximum days with low flow, distribution function of Pearson type 3 for regional 1, 3 and normal for regional 2, pareto for regional 4 were the best methods.