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<br />39 <br /> <br />. <br /> <br />actual flow profile for conditions of tranquil flow (Fr ~ 0.7). <br />However, program PR~FILE is unique among the three in its capacity <br />to calculate a continuous profile for flows near critical in a single <br /> <br />run on the computer. The most severe cases encountered in the study <br /> <br />area were between stations 214+00 and 334+00. Some of the restricted <br /> <br />cross-sections in chutes are shown in Appendix E, Figures E-l, E-7 <br /> <br />and E-8 for stations 331+00, 332+00 and 333+00. The most severe <br />channel slopes were 0.075. Calculated and measured water surface <br /> <br />profiles are also shown in Figure E-l5. A number of isolated computed <br /> <br />points were one order of magnitude higher than the observed profile. <br /> <br />These points were associated with a short reach of accelerated flow, <br /> <br />such as a contraction, after which the water surface would drop to <br /> <br />the supercritical level for a short distance. Since this occurrence <br /> <br />was isolated, it is felt that it does not significantly detract from <br /> <br />utility of the program. Points where the measured water surface drops <br /> <br />should be easily identifiable from a field survey, then some possible <br /> <br />deviation should be anticipated in the computed profile. If such a <br /> <br />condition would develop as a result of stream modifications, the water <br /> <br />surface elevations calculated by the program at the point of occurrence <br /> <br />would be greater than in the field, although velocity calculations <br /> <br />would be too low. However, based on the observations of many investi- <br /> <br />gators, there should be reasonable assurance that the mean velocity <br /> <br />would not exceed about 20 feet per second in natural streams. Observed <br /> <br />velocity in the chute shown in Figure E-7 was near 18 feet per second. <br /> <br />~ <br /> <br />. <br /> <br />, <br /> <br />~ <br /> <br />. <br /> <br />Utility of the Program for Modeling <br /> <br />All three of the programs, USGS, USBR and PR~FILE, were used to <br /> <br />determine the effects of alterations to various stream cross-sections. <br />