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<br />., <br /> <br />. <br /> <br />'\ <br />, I <br />'-- <br /> <br />rJ <br />..., <br /> <br />. <br /> <br />'-' <br /> <br />~ 8 ,- I <br />iJ .,H <br /> <br />Regime Width Analysis <br /> <br />An analysis was made to determine if the open'channe1 width of the <br />Platte River as shown on the 1938 aerial photographs Yith variation <br />from 2,000 to 3,000 feet could be supported by a regime width formula. <br />Several of these formulas were tried such as those of Lacey, Bose, <br />Enge1und and Hansen" Blench, and the Bureau formula developed for <br />the Navajo Indian Irrigatio~ Project. The dominant,discharge was <br />computed at aboat 1+,000 ft /s from the Overton gage records from <br />1915 to 1938. With this dominant discharge, the computed regime <br />widths were as follows: <br /> <br />Formula <br /> <br />Width in feet <br /> <br />Lacey <br /> <br />W ~ 2.7Q.5 <br /> <br />W a 2.8Q.5 <br /> <br />W ~ .78Q.525 <br />D .316 <br />'. 50 <br /> <br />522 <br /> <br />283 <br /> <br />Bose <br /> <br />294 <br /> <br />Engelund and <br />Hansen <br /> <br />(metric) <br /> <br />Blench <br /> <br />(:: ) <br /> <br />.5 <br />Q.5 <br /> <br />1,170 <br /> <br />W~ <br /> <br />USBR <br /> <br />W a 4,24Q.5 <br /> <br />445 <br /> <br />where: <br /> <br />Q <br /> <br />3 <br />- 11,000 ft /s <br /> <br />D50 a 0.73 mm (from bed mate+ial samples at <br />Overton in 1953 and 1956) <br /> <br />Fb - 2.5 <br />F a 0.02 <br />s <br /> <br />(from high-discharge flow <br />measurements at Overton gage <br />1940 t'J 1949) <br /> <br />The above formulas show that, prior to 1938, the Platte River was not <br />in regime either caused by an extreme braided or aggrading condition <br />'and possibly affected by the ice jams that occurred each year. The <br />Blench equation gave the best check on widths in the south channel <br />in 1938 and 1971 and for the main channel in 1971. <br />