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In the formulas in present use the resistance coefficient has been considered constant for a particular type of material in a particular state of upkeep. The resistance coefficient, however, is not a constant for a given channel but varies with both velocity and depth. From the nature of these formulas in present use it may be seen that the variable influence of viscosity is not taken into consideration. Because of the need for more accurately determining the discharges in open channels a standard for roughness for open channels such as that which exists for pipes is desirable. The problem of developing a reproducible standard for roughness in open channels has previously received very little systematic study. Although several investigations have been made, each was made with a different type of roughness. This study was conducted for the purpose of determining whether an artificial roughness standard could be established for a channel with a boundary so rough that the viscous effects were negligible. The equation was established and is applicable over at least a fourfold variation in d/a and nearly a twofold variation in the resistance coefficient.