Programme  OS1s Hydrological diagnosis and forecasting: Advanced computational approaches  abstract 318

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(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 .

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Session: OS1s Hydrological diagnosis and forecasting: Advanced computational approaches
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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