Background of Program: In developing a water resources atlas for the State of Utah it was necessary to determine the characterisitcs of stream flows within the State. The variations of stream flow for any given month from year to year as well as the variations from month to month throughout the year are important characterisitcs which are determined by analyzing the streamflow records to determine their probability distributions. The program which is descirbed in the following pages was written to determine the monthly as well as annual runoff amounts which might be expected for any number of specified levels of probability. Since all streamflow data does not follow the same distribution function, the program has been designed to fit the data to any or all of the following four distribution functions which are commonly used. 1. The normal distribution; 2. The distribution actually obtained from the data by ranking it from high to low; 3. The gamma distribution; and 4. The long-normal distribution. The program has been written specifically to determine the monthly and annual runoff volumtes in ac-ft and also in inches over the watershed. The program could, however, serve equally well for determining monthly and annual amounds of other quantities at specified levels of probabilities after very minor modifications.
Jeppson, Roland W., "Frequency and Magnitudes of Monthly and Annual Flow Rates (As Determined By (a) A Normal Distribution (b) By Ranking (c) A Gamma Distribution And (d) By A Log Normal Distribution)" (1967). Reports. Paper 314.