Investigation on regional relations of annual water yield estimation on different return period in 8 Region of country-Region 6

Water resources scarcity is one the main limiting factors for growth and sustainable development in every region and affects all of the short and long term plans. In addition, water resources managements are characterized with several components and special complexity in a basin scale. This complexity and affecting factors should be recognized in an integrated watershed management plan. For satisfying these requirements, annual water yield with different return periods have been recognized in Soil Conservation and Watershed Management Institute mandate as a research priority. In 2006, national research project of and quot;Regional analysis of water yield in different return periods in 8 restricted areas of Iran and quot; was approved by the Institute as a special project and a part of the Watershed Features Integrated Plan. Restricted area number 6 (Region 6) comprises of several main basins including of Hendijan-Jarrahi, Shahpoor-Dalaki, Mond-Sheshpir, Kol-Mehran and Bakhtegan in Fars, Kohgilooyeh-Bowar Ahmad, Booshehr, Khoozestan and Hormozgan province. The area, perimeter, mean basin elevation, length of main drainage, equivalent rectangle length, basin slope, main river slope, drainage density, Gravilios coefficient and mean annual precipitation in different return periods are the parameters were used in this project. Also, SPSS software was used for homogeneity analysis of the basins by cluster analysis. In cluster analysis the basins were categorized in the three homogene groups. In factor analysis for regional relationships the area, mean basin elevation, length of main drainage, equivalent rectangle length, main river slope, and mean annual precipitation were significant in group 1, area, perimeter, length of main drainage, main river slope, Gravilios coefficient and mean annual precipitation were significant in group 2 and finally area, mean annual precipitation, length of main drainage and drainage density were significant in group 3. Therefore, area, mean annual precipitation, main river length as three main affecting factors were seen in the whole region. In the regional relationships of discharge with area, precipitation and equivalent rectangle length parameters in group 1, precipitation, area, and Gravilios coefficient in group 2, and precipitation, area, main drainage length and drainage density in group 3 had direct relationship, but the negatively related with the other factors. In addition, discharge regression coefficient with other factors in different return periods was highly significant (0.001). In an evaluation, comparing the results with different stations data showed that observed and predicted data were highly correlated. The results of this research showed that the area, as an available important variable, could not predict discharge, especially in group 3. In addition, recognizing single regression of discharge with precipitation was not well correlated, but specific discharge and precipitation were highly correlated in different return periods. Multiple regression analysis showed that specific discharge with precipitation and area were highly correlated in regional relation, but the discharge showed less correlation with these two variables. Finally, the result showed specific discharge by two available factors of precipitation and area, which one related to climate and the other related to physical properties of the basin, are better obtained than discharge as volumetric flow rate in single or multiple regression analysis.