Updating Culvert and Storm Drain Design and Installation Methods

Hydraulic Efficiencies for Colorado Department of Transportation Type C and D Median Inlets

  • Amanda L. Cox (University of Saint Louis)


A research program was conducted to evaluate the performance of two Colorado Department of Transportation (CDOT) highway median storm drain inlets, Type C and Type D. Inlets tested are currently used by both the Urban Drainage and Flood Control District (UDFCD) of Denver and CDOT. Theoretical flow depth-capacity curves have been developed for the Type C and D inlets, but were not previously laboratory tested. Current design practices are based upon general application of the orifice and/or weir equations. A 3:1 Froude-scale model of a highway median was designed and built to provide data to evaluate the accuracy of the existing rating equations. The model consisted of a constructed highway median channel with one interchangeable inlet. Six types of inlet configurations were tested: on-grade and depressed inlets for Type C, Type D and Type D rotated. A total of 120 hydraulic tests including twenty-four debris tests were performed. Variations in grate angle measured along the slope (0, 10, 20 and 30 degrees) were investigated to provide flow-depth and discharge data for each inlet configuration. Evaluated prototype flow depths ranged from 0.3 to 0.9 m. Resulting stage-discharge data were tabulated and plotted, and qualitative observations were made regarding the hydraulic conditions during testing and debris assessments. Stage-discharge data for the grate inlets were compared to existing methods for computing inlet efficiency, and a new rating equation was developed for median inlets with orifice flow.

How to Cite:

Cox, A. L., (2014) “Hydraulic Efficiencies for Colorado Department of Transportation Type C and D Median Inlets”, National Hydraulic Engineering Conference 2014 1(2014).

Rights: Copyright © 2014, Amanda L. Cox

Publisher Notes

  • Panel moderated by Andrea Hendrickson, MNDOT.
  • About the Presenters: Dr. Cox is an Assistant Professor in the Civil Engineering Department at Saint Louis University (SLU). Prior to joining SLU, she was a Research Scientist and Laboratory Manager at the Colorado State University (CSU) Hydraulics Laboratory where she completed over 70 research projects. Dr. Cox received her BS degree in Civil Engineering from the University of Missouri – Columbia. Subsequently, she received her MS and PhD degree in Civil Engineering from CSU specializing in Hydraulic Engineering. Her experiences include physical and numerical hydraulic modeling encompassing several areas of hydraulic engineering including river modeling, channel rehabilitation structures, bridge pier scour, reservoir outlet works, and erosion control product performance testing.

Download HTML



Published on
22 Aug 2014
Peer Reviewed