Hydraulic Characterization of Relief Culverts

A relief culvert is a road drainage work that is classified as cross drain, since the flowing water crosses the road. It differs from common culverts and bridges in that they are not built to cross streams or rivers. Relief culverts convey water from one side of the road to the opposite side, preventing the overflow of gutters, ditches and swales. This type of culvert is frequently used, especially in hilly roads where cut and fill sections are common. In spite of this, literature and research on the topic are sparse.

Therefore, a physical model was built in order to determine the hydraulic characteristics that describe the flow in a relief culvert. To do so, a clear acrylic physical model was constructed in scale 1:4 following Froude scale law. Discharge, flow velocity and pressure were carefully monitored and recorded. Typical inlet control conditions were tested as well as some outlet control situations, mainly, those where the outlet is not submerged.

From the model it was possible to establish the different flow conditions and patterns that may occur in a relief culvert, a performance curve of the structure is suggested as well as discharge coefficients for submerged inlet control. Finally some preliminary design guidelines are outlined.