Storm water flow on a curbed TxDOT-type concrete roadway, the variation of Manning's n with differing equations, definitions of wetted perimeter, and roadway slopes

In 1946, C. F. Izzard introduced the gutter discharge equation derived via integration of a Manning velocity equation across a gutter section. Literature reviews indicate that Izzard suggested increasing Manning's n values when using the integrated equation. Although the integrated equation is utilized extensively, the suggested increase in Manning's n appears to have not been implemented. There is a discrepancy between the geometric equation (the product of Manning's Mean Velocity Equation and flow area) and the integrated equation that results in overestimation of a gutter's flow capacity when using the integrated equation and traditional Manning's n values.; With intent to improve driving conditions by obtaining more accurate gutter flow computation methods, the derived geometric and integrated equations are evaluated for three definitions of the wetted perimeter of a curbed section. Also, experimental data is evaluated to determine Manning's n for a curbed concrete TxDOT (Texas Department of Transportation) type roadway at various transverse and longitudinal slopes.