County staff says rational-method trigger proves too sensitive; seeks user-friendly tools
Staff tested a McHenry County simplified rational-method trigger and found the results highly sensitive to time-of-concentration and storm-duration inputs; staff recommended either engineer-run rational calculations or hiring external services to develop a defensible tool.
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Staff presented tests of a McHenry County simplified rational-method trigger and reported results vary widely with small changes to time-of-concentration and chosen storm duration. The presenter warned that using a simplified rational approach produced large swings in calculated peak flows depending on assumed durations and that staff does not yet have a defensible, user-friendly tool to replace more detailed hydrograph methods.
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