Investigation and Comparison of the Quantitative and Qualitative Frequency Distribution of the Rivers

The entrance of pollutants from human activities to the surface water has seriously threatened the quality of water. TDS is an important qualitative parameter of water that describes the water salinity by measuring the concentration of total dissolved solids. First, using TDS and discharge data of the Cuyahoga River, Ohio, the partial and annual data sets were obtained. Then, partial data with three thresholds of n, 1.64n and 2n, in which n is the number of statistical years were developed and using the Hyfa Software, the frequency distribution of the data series was done. The results showed that for most cases, the two-parameter Log-normal distribution is the best distribution. Finally, for model validation, the error corresponding to each estimation was first calculated in comparison to the real data for the corresponding return periods. Then, 1.64n partial series was considered as the optimum method suggested by Hasking and a comparison was made between the estimates and this optimum series. The results showed that the series with a length of 2n was closest to the optimum case.