Part 3: Hydrology, Hydraulics, and Water Quality: Hydraulic Characteristics of Buried-Invert Elliptical Culverts

In response to recent and ongoing adaptation of culvert designs to environmentally sensitive installations, inlet loss coefficients and inlet control flow performance data are presented that are specific to environmentally sensitive culvert geometries. A common practice for such culvert designs is to bury the culvert inverts and create a simulated streambed through the culvert. Common cross-sectional geometries of such culverts typically include circular, elliptical, or pipe arch. These buried- or depressed-invert culverts create inlet geometries for which inlet loss information and inlet control flow performance curves have not been developed. Regardless of the method used to design environmentally sensitive culverts, the ability of the culvert to pass the design flood must be determined. In an effort to provide such information, an elliptical smooth-wall culvert with an invert burial depth of 50% was tested under various conditions (e.g., various end treatments, inlet and outlet control, submerged and unsubmerged inlet conditions, and ponded and channelized approach flow conditions) to determine the inlet loss coefficient and flow performance curve characteristics. The test results show that the inlet loss coefficient is relatively independent of both Reynolds number and the ratio of the distance from the inlet invert to the upstream total energy grade line to the culvert diameter (HW/D) and that the inlet loss coefficients for the elliptical culvert with 50% burial depth are approximately equal to the published coefficients for traditional culvert inlets. The inlet control data adapt well to the Form 1 and Form 2 unsubmerged and the submerged equations recommended by FHWA.