Regional analysis of Diferent Return Period annual water yield estimation in 8 Region of Country- Region 4

A comprehensive management of any watershed needs spatial and temporal variation of stream flow generation over the country watersheds, especially over the up stream tributary. Generalization of available information and data from gugaed basin to ungauged needs research and surveying on the variation such factors and their relation to constant and stable parameters of the basins. 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 4 (Region 4) comprises of three main basins including of Karkheh, Karoun and Dez in Kordestan, Kermanshah, Hamedan, Kohgilooyeh-Bowar Ahmad, Khoozestan, Ilam, Chahar-Mahal va Bakhteyari, Lorestan and Esfahan provinces. 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 two homogene groups. There are 179 hydrometery and 269 meteorological stations in the region, that 108 and 208 stations was selected for regional analysis in a 20 years period based on sufficient data. Multiple regression results was used to predict the observed annual water yield of 2 hydrometery stations which were not used in regional regression equations, each for one region. The results showed a high regression coefficient between observed and computed data (0.98 and 0.99). in regional regression analysis, a group of parameters including area, equivalent rectangle length, slope and Gravilios coefficient show direct effects on annual discharge, but the other group including precipitation, main stream length, main stream slope, mean basin elevation, drainage density and perimeter show inverse effects on annual discharge. The above relationship is abnormal for precipitation. In spite of abnormal behaviors of precipitation, the regression coefficient of discharge are 0.57, 0.866, 0.85, 0.849, 0.843, 0.83 for the first group and 0.989, 0.866, 0.866, 0.99, 0.98 and 0.98 for the second group in 2, 5, 10, 25, 50 and 100 return periods respectively which are highly significant (K 0.001). The results of this research showed that the area, as an available important variable, could predict discharge with high correlation (0.83, 0.85, 0.84, 0.81 and 0.79 in 2, 5, 10, 20, 25 and 100 return periods respectively). 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. Also these relations show a decreasing rate of regression coefficient with increasing in return periods. Multiple regression analysis showed that specific discharge (mean depth over basin) with precipitation and area were highly correlated in regional relation, but the discharge showed less correlation with these two variables. In addition,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. Finally, this research focused on regional analysis of mean annual discharge in different return periods for region 4, we emphasized on using the methods for the other base time such as monthly and over country basins.