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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I, <br />I <br />I <br />I <br />I <br />I <br />I <br />r <br />I <br />I <br /> <br />C=.1821 <br /> <br />Table 7.4 1M Site flow distribution for modeled recurrence intervals <br /> <br /> Recurrence Interval Discharge <br />Location Q\.l Q1.5 Q2 Q5 Q10 Q25 Q50 Q75 Q100 <br />1M Site 1 Tota[ Discharge (cfs) 358 553 669 915 1060 1210 1310 1370 1400 <br /> In-Channel Discharge (cfs) 358 545 655 888 1022 1158 1248 1302 1334 <br />1M Site2 Tota[ Discharge (cfs) 464 680 818 1200 1480 1870 2180 2400 2510 <br /> In-Channel Discharge (cfs) 464 675 8[0 1190 [329 1449 1495 1562 1599 <br />1M Site 3 Total Discharge (cfs) 464 680 818 1200 1480 1870 2180 2400 2510 <br /> In-Channel Discharge (cfs) 464 618 808 949 1024 I I 14 1163 1205 12 I 8 <br />1M Site4 Total Discharge (cfs) 464 680 818 1200 1480 1870 2180 2400 2510 <br /> In-Channel Discharge (cfs) 464 680 818 113\ 1\57 139\ \556 \665 174\ <br />1M Site 5 Total Discharge (cfs) 464 680 818 1200 1480 1870 2180 2400 2510 <br /> In-Channel Discharge (cfs) 464 679 814 1104 1172 1378 1526 1618 1667 <br />1M Site 6 Total Discharge (cfs) 464 680 818 1200 1480 1870 2180 2400 2510 <br /> In-Channel Discharge (cfs) 464 680 813 991 II 18 1310 1460 1555 1606 <br /> <br />7.3.2. Model Construction and Calibration <br /> <br />Data available for model construction consisted of cross-section surveys, discharge <br />calculations, topographic maps, and an HEC-RAS floodplain model developed by URS. <br />A total of six hydraulic models were constructed, one for analysis of each 1M site. Each <br />model used a combination of cross-section survey data and topographic mapping. <br />Following development of model geometry, calibration was accomplished by varying <br />Manning's roughness coefficients (n-values) and contraction and expansion coefficients <br />within the model to match measured water surface elevations for specific discharges. <br /> <br />Cross-section surveys and discharge calculations were performed at relatively low-flow <br />levels for cross-sections AR-O, AR-I0, and AR-20. Influences from multiple hydraulic <br />controls made low-flow model calibration difficult and generated extremely large n- <br />values, ranging up to 0.15. This was a result of numerous small channel bed features <br />acting as hydraulic controls at low flows. Not all of the bed feature controls were <br />represented by cross-sections, resulting in inordinately high n-values to compensate for <br />the influence of the controls. At higher flows, the influence of these controls becomes <br />minimal. Other techniques for n-value estimation were used, including multiple <br />empirical equations developed by Cowan (1956), Limerinos (1970), and Jarrett (1984), <br />Manning's equation, and water surface elevation calibration techniques (USGS, 1989). <br /> <br />May 7. 1999 <br /> <br />Pluvial Geomorphological Assessmen/ <br />Upper Arkansas River <br /> <br />Page 55 <br />