 The U.S. National Weather Service defines Johnson Creek's flood stage, measured at USGS station 14211500 at Sycamore in Portland, as , equivalent to a flow rate (discharge rate) of about per second.The USGS peak streamflow data collected by the stream gauge at that station show that the creek reached or exceeded per second 37 times between 1941 and 2006; that is 37 floods in 65 years.Twenty of those floods exceeded per second.