Laserfiche WebLink
<br />x = [ X <br />N <br /> [ L (x - X)2 ] 0.5 <br />5 = <br /> (N-ll <br /> [ (L X2) - d:: X)2JN ] 0.5 <br /> = <br /> (N-ll <br />G = N L (X_X)3 53 <br /> (N-l) (N-2) <br /> = N2( L X3) - 3N( EX) ( L X2)+2( r X)3 <br /> N(N - 1) (N - 2) 53 <br /> <br />(2) <br /> <br />(3a) <br /> <br />(3b) <br /> <br />(4a) <br /> <br />(4b) <br /> <br />in which: <br /> <br />X = logarithm of annual peak flow <br />N = number of items in data set <br />X = mean logarithm <br />5 = standard deviation of logarithms <br />G = skew coefficient of logarithms <br /> <br />Formulas for computing the standard errors for the statistics X, S, and <br />G are give in Appendix 2. The precision of values computed with equations <br />3b and 4b is more sensitive than with equations 3a and 4a to the number <br />of significant digits used in their calculation. When the available <br />computational facilities only provide for a limited number of significant <br />digits, equations 3a and 4a are preferable. <br />The skew coefficient of the station record is sensitive to extreme <br />events; thus it is difficult to obtain an accurate estimate from small <br />samples, and use of a generalized estimate of the skew coefficient is <br />recommended when estimating the station skew for short records. As the <br />length of station record increases, the skew computed from individual <br />station data is usually more reliable. Specifically, if records of 100 <br />years or more are available, the station skew should be used exclusively. <br /> <br />10 <br />