بررسي روش‌هاي تعيين ضريب چولگي منطقه‌اي حداكثر دبي لحظه‌اي در استان آذربايجان شرقي

Investigation of Methods for Determining the Regional Skewness Coefficient of the Maximum Discharge in East Azarbaijan province

در ﺗﻌﯿﯿﻦ دﺑﯽ ﺑﺎ دورهﻫﺎي ﺑﺎزﮔﺸﺖ ﻣﺨﺘﻠﻒ، ﻻزم اﺳﺖ ﮐﻪ ﺿﺮﯾﺐ ﭼﻮﻟﮕﯽ ﺑﺎ دﻗﺖ ﻗﺎﺑﻞ ﻗﺒﻮل ﻣﻮرد اﺳﺘﻔﺎده ﻗﺮار ﮔﯿﺮد. ﺑﺮآورد ﭼﻮﻟﮕﯽ ﺟﺎﻣﻌﻪ در ﻣﻨﺎﻃﻖ ﻣﺨﺘﻠﻒ، ﺑﺎ روشﻫﺎي ﻣﺨﺘﻠﻔﯽ ﻫﻤﭽﻮن ﭼﻮﻟﮕﯽ ﺗﻮزﯾﻦﯾﺎﻓﺘﻪ و ﭼﻮﻟﮕﯽ ﺗﻌﻤﯿﻢﯾﺎﻓﺘﻪ ﺑﻬﺒﻮد ﻣﯽﯾﺎﺑﺪ. ﻫﺪف از اﯾﻦ ﺗﺤﻘﯿﻖ ﺗﻌﯿﯿﻦ ﺿﺮ اﯾﺐ ﭼﻮﻟﮕﯽ ﺑﺎ روشﻫﺎي ﻣﺨﺘﻠﻒ و ﻣﻌﺮﻓﯽ ﺑﻬﺘﺮﯾﻦ روش ﺗﻌﯿﯿﻦ آن ﺿﺮاﯾﺐ در اﺳﺘﺎن آذرﺑﺎﯾﺠﺎن ﺷﺮﻗﯽ اﺳﺖ. اﺳﺘﺎن آذرﺑﺎﯾﺠﺎن ﺷﺮﻗﯽ داراي ﺳﻪ ﻣﻨﻄﻘﻪ ﻫﯿﺪروﻟﻮژﯾﮏ ﻣﺘﻔﺎوت اﺳﺖ. ﺷﻤﺎل اﺳﺘﺎن ﺟﺰء ﺣﻮﺿﻪ آﺑﺮﯾﺰ ارس، ﻣﺮﮐﺰ اﺳﺘﺎن ﺟﺰء ﺣﻮﺿﻪ آﺑﺮﯾﺰ درﯾﺎﭼﻪ ي اروﻣﯿﻪ و ﻗﺴﻤﺘﯽ از ﺟﻨﻮب اﺳﺘﺎن ﺟﺰء ﺣﻮﺿﻪ ي آﺑﺮﯾﺰ ﺳﻔﯿﺪرود ﻣﯽﺑﺎﺷﺪ. در اﯾﻦ ﺗﺤﻘﯿﻖ از روشﻫﺎي ﻣﺨﺘﻠﻒ ﺿﺮﯾﺐ ﭼﻮﻟﮕﯽ ﺗﻌﻤﯿﻢﯾﺎﻓﺘﻪ اﺳﺘﻔﺎده ﮔﺮدﯾﺪ. در ﻣﻄﺎﻟﻌﻪ ﺣﺎﺿﺮ، ﺿﺮاﯾﺐ ﭼﻮﻟﮕﯽ ﺗﻌﻤﯿﻢﯾﺎﻓﺘﻪ ﺑﻪ ﭼﻬﺎر روش ﺿﺮﯾﺐ ﭼﻮﻟﮕﯽ ﺗﻌﻤﯿﻢﯾﺎﻓﺘﻪ ﺑﺪون در ﻧﻈﺮ ﮔﺮﻓﺘﻦ ﻣﻨﺎﻃﻖ ﻫﯿﺪروﻟﻮژﯾﮏ، ﺿﺮﯾﺐ ﭼﻮﻟﮕﯽ ﺗﻌﻤﯿﻢ ﯾﺎﻓﺘﻪ ﺑﺎ در ﻧﻈﺮ ﮔﺮﻓﺘﻦ ﻣﻨﺎﻃﻖ ﻫﯿﺪروﻟﻮژﯾﮏ، ﺿﺮﯾﺐ ﭼﻮﻟﮕﯽ ﻧﺎارﯾﺐ و ﺿﺮﯾﺐ ﭼﻮﻟﮕﯽ ﺗﻮزﯾﻦﯾﺎﻓﺘﻪ ﺑﺮاي ﻣﻨﺎﻃﻖ ﻫﯿﺪروﻟﻮژﯾﮏ ﺳﻪﮔﺎﻧﻪ و 62اﯾﺴﺘﮕﺎه ﻣﺸﺎﻫﺪاﺗﯽ ﻃﯽ دورهﻫﺎي ﻣﻮرد ﻣﻄﺎﻟﻌﻪ ﺑﺮآورد ﮔﺮدﯾﺪ. ﺑﺮ اﺳﺎس ﻧﺘﺎﯾﺞ ﺑﻪ دﺳﺖ آﻣﺪه ﺑﺮ اﺳﺎس ﺗﺠﺰﯾﻪ و ﺗﺤﻠﯿﻞ ﻣﻘﺎدﯾﺮ RMSEﺑﺎ اﺳﺘﻔﺎده از روشﻫﺎي ﻣﺨﺘﻠﻒ ﻣﯽﺗﻮان روش وزندﻫﯽ ﺑﻪ ﺿﺮﯾﺐ ﭼﻮﻟﮕﯽ ﺑﺎ ﻣﻘﺪار ﻣﯿﺎﻧﮕﯿﻦ 0/104را ﺑﻪ ﻋﻨﻮان روش ﺑﺮﮔﺰﯾﺪه در اﺳﺘﺎن آذرﺑﺎﯾﺠﺎن ﺷﺮﻗﯽ ﭘﯿﺸﻨﻬﺎد ﻧﻤﻮد. ﻫﻤﭽﻨﯿﻦ ﻧﺘﺎﯾﺞ ﺣﺎﺻﻞ از ﻣﺤﺎﺳﺒﻪ ﺿﺮاﯾﺐ ﻧﺶ ﺷﺎﺗﮑﻠﯿﻒ و ﻣﺠﺬور ﻣﯿﺎﻧﮕﯿﻦ ﻣﺮﺑﻌﺎت ﺧﻄﺎي ﻧﺴﺒﯽ ﻧﺸﺎن داد روش وزندﻫﯽ ﺑﻬﺘﺮﯾﻦ روش ﻣﺤﺎﺳﺒﻪ ﺿﺮﯾﺐ ﭼﻮﻟﮕﯽ اﺳﺖ.

To determine the flow rate with different return periods, it is necessary to use the skewness coefficient with acceptable precision. Estimation of population skewness in different regions is improved by different methods such as weighted skewness and generalized skewness. The main objective of the present research is to determine the coefficients of skewness using different methods and present the best method for determining the mentioned coefficients in East Azerbaijan, Iran. East Azerbaijan has three different hydrologic regions. The north of the province is a part of Aras catchment area, the center of the province is a part of Urmia lake watershed and a part of the south of the province is a part of Sefidrood catchment area. In this research, different generalized skewness coefficients methods were used. In the present study, the generalized skewness coefficients were estimated using four methods including generalized skewness coefficient without considering hydrological regions, generalized skewness coefficient with accounting hydrological regions, unbiased skewness coefficient and weighted skewness coefficient for three hydrological regions and 62 observed stations during studied period. Based on the obtained results and on the basis of the analysis of RMSE values for different methods, the method of weighting skewness coefficient can be suggested as the selected method in East Azerbaijan with an average value of 0.104. Also, the results of calculating the Nash-Shutcliffe and the square of the mean squares of relative error coefficients showed that the weighting method is the best method for calculating the skewness coefficient.