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<br />Table 3. Statewide channel-geometry characteristic equations for estimating design-flood discharges <br />in Iowa <br /> <br />[Q, peak discharge, in cubic feet per second, for a given recurrence interval, in years; BFW, bankfull <br />width, in feet; BFD, bankfull depth, in feet; ACW, active-channel width, in feet] <br /> <br />Estimation equation <br /> <br />Standard <br />error of estimate <br />LoglO Percent <br /> <br />Average <br />standard error <br />of prediction <br />(percent) <br /> <br />Average <br />equivalent <br />years of <br />record <br /> <br />Bankfull equations <br />Number of streamflow-gaging stations = 111 <br /> <br />Q2 = 4.56 BF'WO.982 BFDl.02 0.169 40.4 41.0 4.2 <br />Q5 = 14.7 BF'WO.915 BFDo.899 .173 41.5 42.2 4.6 <br />QlO = 26.7 BF'WO.874 BFDo.846 .186 44.9 45.8 5.1 <br />Q25 = 49.5 BF'WO.828 BFDo.797 .206 50.2 51.4 5.8 <br />Q50 = 73.2 BF'WO.796 BFDo.769 .221 54.4 55.8 7.0 <br />QlOO = 104 BF'WO.766 BFDo.747 .236 58.7 60.4 8.5 <br /> Active-channel equations <br /> Number of streamflow-gaging stations = 157 <br />Q2 = 38.5 ACW1.06 0.267 67.8 68.3 1.6 <br />Q5 = 98.2 ACWO.98O .247 61.9 62.3 2.1 <br />QlO = 157 ACWO.937 .246 61.5 61.9 2.8 <br />Q25 = 256 ACWO.891 .251 63.0 63.6 3.6 <br />Q50 = 349 ACWO.861 .258 65.1 65.8 4.8 <br />QlOO = 458 ACWO.833 .267 67.7 68.4 6.3 <br /> <br />Note: Bankfull equations may provide improved accuracies over active-channel <br />equations for channels unaffected by channelization. For channels affected by <br />channelization, the active-channel equations only are applicable when the active <br />channels have stabilized (approximately 5 to 10 years after channelization). See <br />Appendix C for a discussion of stabilized channels. <br /> <br />~ <br /> <br />ESTIMATING DESIGN.FLOOD DISClIARGES USING CHANNEL-GEOMETRY CHARACTERISTICS 23 <br />