Summary

The objective of this study was to determine current and future development condition frequency functions to be used in flood damage analysis in the CRS watershed. To calculate the increase in EAD, the analyst needed the current and future development flow-frequency functions. Using an available calibrated rainfall-runoff model of current development in the watershed, precipitation events of known frequency were used in HEC-HMS to compute a flow-frequency function. Eight precipitation frequency events were used to ensure adequate resolution of this function. The flow-frequency function developed was then compared to functions developed using alternative procedures. A best-estimate current development condition frequency function was then adopted. Then, the rainfall-runoff model was altered to reflect the watershed with future development. For both development conditions, several methods, as shown in the Alternative Methods for Deriving Flow-Frequency Functions and discussed in the text, can be used to compute flow-frequency functions.