Subdivision Froude number

A Froude number that is applicable to subdivisions of a cross section is developed assuming one-dimensional flow. The subdivision Froude number is shown to be an accurate index of the flow regime in subdivisions of a cross section. An imaginary Froude number in a flood plain indicates that the velocity is increasing with depth and that a one-dimensional flow assumption may be invalid. Mixed flow regimes at a cross section which invalidate assumptions associated with the standard step method can be recognized with the subdivision Froude number. A total of 193 cross section-discharge combinations were tested with a modified version of HEC2; 11 had a mixed flow regime and 36 had at least 1 imaginary Froude number.