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An investigating the effects of generalized skew coefficient(third moment ) on instantaneous annual maximum discharges. (case study : Dez basin in south western of Iran)

Author(s): Hydrology
Congress: 2008
Author(s): Nasser Tahmasebi(1) , Mohammad Mahdavi(2), Frood Sharifi(3), Hamid Pezeshk(4), Sayed Mahmood Reza Tabatabaei(5)
(1) Nasser , Tahmasebi , Assistant professor in university of Lorestan , Faculty of Agricultural (2) Mohammad , Mahdavi , professor in university of Tehran , Faculty of Natural Resources . (3) Forood , sharifi , Assistant professor in soi

Keyword(s): Generalized coefficient ,Hydrometeric station skewness , Instantanous maximum discharge , Dez busin .
AbstractAbstract One of the methods of reduce flood hazard is correct estimation discharge designing of water structures , because without computation of estimated discharge water structures is destroy by flood occurance and increase flood hazard power . use of masurment data in gauging stations in the area is the best method for estimation discharge flood design . Also computation of generalized coefficient skewness of masurmented data decrease estimated error and water structures dimensions improve designing . The study is Located 47 Degree and 39 Minute to 50 Degree and 21 minute in Eastern Langth and 31 Degree and 15 Minute to 34 Degree and 33 Minute in Northern Latitude . selected 24 gauging station and then The test of outlier was conducted by using statistical parameters of peak flow in the hydrometric stations , and it was detemined that there are no outlier points among data . SO completing and lengthening for common statical period performed . Then statistical distribution of aforementioned data was fitted . Using griding method , the centeriod of high area of each hydrometric station was determined eneralized skewness coefficients of points then were computed using the unbiased skewness coefficient , the weight coefficient of data and the distance of each hydrometric gauge from centeriod of sub - basin . Spline ( Smooth plate Line ) method was applied to generalize the skewness with the mean square error of %34 . The results show that the range of percentage of differences between unbiased and generalized skewnesses are from 58% to 137%. The observed data have been fitted well with the normal distribution . using this method results less differences between observed and estimated values of peak discharges as where generalized skewnesses were used , the differences of peaks for return periods of 2 , 100 and 1000 years , were %12 , %77 and %180 respectively . It can be concluded that the fitness of selected probability distribution with the data is quite best using the generalized skewness in estimation of peak discharge .
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