Laserfiche WebLink
<br />events np to the lOO-year, the then the hydrolo~~c' model can ignore the tributary area. <br /> <br />5.5 Storm Patterns and Distribution <br />There are two types of flood producing rain storm events in Colorado, thunderstorms and general <br />rains, There are distinct patterns and intensities for each type of storm which must be identified <br />to adequately distribute the rainfall over a drainage basin, <br />Issues: What are the eenerally accepted intensitie:!.iIuration. and patterns for the rainfall <br />events? How can the policy issues be defmed? <br /> <br />5,6 Methods <br />5,6,1 Statistical Analvsis of Determining Hood Hvdrologv <br />The use of statistical methods for detennining flood hydrology IS a common one; <br />however, in Colorado the records for flood peaks are affected in some cases due to stream <br />diversion or reservoir storage. Discharge-frequency analysis requires at least 10 years of <br />data for a reasonable analysis (17B, pg :20), Methods in Bulletin l7-B are recorrunended <br />for statistical analyses to provide a consistent and uniform technique nationally. There <br />are st<veral options outlined in 17B for determining skew values which include the map <br />in Bnlletin 17-B, predictive equations methods, and the weighted average approach, The <br />use of a state-wide map of skew values would be the ideal tool for establishing the <br />desired consistency and detail not currently available, Until such time as a state-wide <br />skew map is made, available, the methods outlined in Bulletin l7B are the standard <br />practice. <br /> <br />Expected Probability is an adjustment based on an average of true probabilities of all <br /> <br />magnitude estimates for any specified flood frequencies that might be made from <br /> <br />successive samples of a specific size, It represents a measure of the central tendency of <br /> <br />the spread between the confidence limits, This procedure is not a widely used method <br /> <br />in determining flood hydrology through frequency analysis. Expected Probability is <br /> <br />considered only for the design of structural work and estimates of annual flood damages, <br /> <br />6 <br />