The Selection of Rain Distribution Analysis Method in Downstream Sub-Watershed: Bengawan Solo Watershed

摘要

Hydrological factor causes the flood. Thus, it needs to be examined through rain frequency analysis by using continuous chance distribution. The location of this research is at the downstream sub-watershed of Bengawan Solo River. Average rainfall inflow area is calculated by Polygon Thiessen method with 19 (nineteen) different areas depending on the distribution of rain in each station. Frequency distribution analysis and its suitability test use 2 instruments which are a Smirnov-Kolmogorov test and Chi-Square Test. The used distribution applications are Normal Distribution, Normal Log Distribution, Gumbel Distribution and Pearson III Log Distribution. The result of Chi-Square for normal and lognormal distributions is 3,833, also Gumbel and log Pearson III distribution in the amount of 1,333. The result of Smirnov-Kolmogorov for normal distribution = 0,172, Critical normal log = 0,154, Critical Gumbel distribution = 0,119 and Critical log Pearson III distribution = 0,101. The four distributions are accepted but the best distribution is log Pearson III distribution.