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An investigation the effects of generalized skew coefficient (Third moment) on instantaneous annual maximum discharges.

Author(s): Hydrology- Flood estimation
Congress: 2008
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: Phone: +986614200191 -Fax: +986614200289 Presentation: oral Sub-theme: Hydrology-Flood

Keyword(s): Generalized coefficient, Hydrometric, station skew, Instantaneous maximum discharge, Dez basin.
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 occurrence and increase flood hazard power. Use of data in gauging stations in the area is the best method for estimation discharge flood design. Also computation of generalized coefficient skew of measurement data decrease estimated error and water structures dimensions improve designing in the basin without gauging stations or with short data. The study is located in 47 degree and 39 minute to 50 degree and 21 minute in eastern length and 31 degree and 15 minute to 34 degree and 33 minute in northern latitude. We selected 24 gauging stations. 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 statistical period performed. Then statistical distribution of aforementioned data was fitted. Using griding method, the centroid of high area of each hydrometric station was determined generalized skew coefficients of points then were computed using the unbiased skew coefficient , the weight coefficient of data and the distance of each hydrometric gauge from centroid of sub-basin. Spline (Smooth plate Line) method was applied to generalize the skew with the mean square error of %34. The results show that the range of percentage of differences between unbiased and generalized skew 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 skew 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 skew in estimation of peak discharge.
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