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by the median axis of the particle. The equation 0.031 K1/6 is appli- cable to flows at high river stages and is not appropriate for low flows. In both the Chezy and Manning formulae, the slope required as an input is the slope of the energy grade line. This slope is defined as the difference in total energy at two (or more) channel sections, divided by the distance between them. The total energy at a channel section is found with the open channel form of the Bernoulli equation: 2 C6) H=z+d+ where, H = total energy head, in feet (meters) z = elevation of the bed, in feet•(meters) d = average depth for section, in feet (meters) V = average velocity in feet per second (meters per second) g = acceleration of gravity, 32.2 ft/sect (9.8 m/sec ). For practical purposes, it can be seen (Figure=2) that the terms z. + d equal the water surface elevation for a given cross section. Refer- ring to Figure 2, the slope of the energy grade line is: S = H2 H1 (7) - L3 If the assumption is made that flow in the channel is uniform, then the bed slope, hydraulic slope,.and energy slope: are considered equal, So = Sh = Se. PREDICTING THE STAGE-DISCHARGE RELATIONSHIP The determination of the relationship between the stage at a cross section and the discharge associated with that stage must be considered the initial step in the type of simulation used for instream flow assessments. Once the stage has been determined for a certain dis- charge, its elevation is used for simulation in two ways: (1) The depth distribution is found for each cross section by subtraction of bed elevations across the channel from the stage. Thus, if the stage and bed elevations are known, the depth may be determined at any location on the cross section; and (2) The stage identifies the location of the free surface, and is used to establish boundaries for some of the equations used to describe the velocity distribution. Several approaches may be used in the prediction of the stage discharge relationship. Approaches described in this section include: (1) Use of Manning's equation, uniform flow assumed; (2) Calculation of 1 / 0