Programme  Poster session 2  abstract 334

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
Author(s): Nasser Tahmasebi, Mohammad Mahdavi, Forood Sharifi, Hamid Pezeshk, Sayed Mahmood Reza Tabatabei
1.Nasser , Tahmasebi , Assistant professor in university of Lorestan , Faculty of Agricultural Email : tahmasebi Phone :+986614200191 - Fax:+986614200289 Presentation : oral Sub-theme : Hy

Keyword(s): Generalized coefficient ,Hydrometeric station skewness , Instantanous maximum discharge , Dez basin

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Session: Poster session 2
AbstractOne 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 determined 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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