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29 . a contraction will have a lower velocity at the upper section, due to continuity and the larger area of the upper section; thus a velo- city decrease in the upstream direction indicates a contraction. By analogous reasoning, a velocity increase indicates an expansion, While it is known that contractions and expansions are responsible for energy losses, quantitative determination of such losses has not been developed to date. Based on field experience, the USBR uses coef- ficients applied to differences in velocity heads for eddy losses. Coefficients of 0.10 and 0.50 respectively, are applied to contractions and expansions. The USCE uses values of 0.10 and 0.30, respectively. For the case of steep mountain streams, the higher expansion losses are assumed to be more applicable. The larger expansion losses are due to the large energy losses associated with separation and att~ndant turbulent eddies. . . . . Operation of Program PR~~ In the computational sequence, values for area and velocity from the downstream section are assumed for the adjacent upstream section. The elevation head and depth are added to the velocity head, and the friction and eddy losses are subtracted and the remaining energy is compared to energy at the downstream station. An adjustment is then made, if required, to the water level at the upstream station. Adjust- ments, which are based upon the computed difference in energy values, will continue to be made until the computed difference is within a satisfactory tolerance or the limit of iterations is reached. If the energy level cannot be computed to a satisfactory tolerance within the limit of iterations, a flow condition near critical is indicated.