NONZERO LOWER LIMIT IN LOW-FLOW FREQUENCY-ANALYSIS

The implications of fitting distributions with non-zero lower limits t o low flow data are examined. The 3-parameter Weibull distribution is fitted to annual minimum now series from 60 long term stations in Cana da. The relations between the estimated lower limit and three sampling variables (skewness, smallest, and largest observations) were investi gated. The lower limit strongly depends on the sample skewness; it var ies directly with the sample skewness, which in turn is highly influen ced by the largest observation. For a given skewness, the value of the estimated lower limit is determined by the value of the smallest obse rvation. Therefore, the lower limit cannot be accurately determined, a nd the resulting low flow estimates will be either too small or too hi gh.