Hydraulics of Multibarrel Culverts under Inlet Control

The hydraulic characteristics of multi- and single-barrel circular culverts were compared in this study. One-, two-, and three-barrel culverts configurations, operating under inlet control, were tested in the laboratory with various approach conditions and barrel spacing (horizontal and vertical). The single-barrel head-discharge relationship was consistent with the average head-discharge relationship of the individual barrels in a multibarrel culvert configuration with a uniform upstream approach flow and uniform invert elevations. For the nonuniform approach flow condition, the single-barrel model overpredicted the average-barrel flow by up to 10%. With the middle barrel installed at a lower elevation than the outside barrels, in submerged flow the single-barrel head discharge relationship was consistent with the outside barrels, but the middle barrel was up to 7% more efficient than the single-barrel discharge. The flow rate variations are attributed, in part, to a reduction in approach flow contraction entering the center culvert in the three-culvert configuration and a nonuniform distribution of intermittently forming surface vortices at the culvert inlets. The results of a state (United States) Department of Transportation survey regarding multiple culvert use are also presented.