Research Project Full Title: Analysis of Curb Inlets in the New TxDOT Standard Inlet and Manhole Program
Principal Investigator(s): Assoc. Prof. Ben R Hodges and Prof. Michael E Barrett
Researchers: Muhammad Ashraf and Frank Schalla
Sponsor(s): Texas Department of Transportation
Full Abstract: Curb-opening inlets are among the commonly used storm drain inlets, which collect and convey storm-water runoff on roadways to subsurface sewer networks. Hydraulic Engineering Circular No. 22 (HEC-22) contains the FHWA’s recommended design equations for curb inlets. These equations assume a linear decrease of the water surface profile along the inlet length. A full scale physical model is used to evaluate HEC-22 design equations for 5, 10, and 15 ft inlet lengths. Results show that the latter part of a long inlet does not have a simple linear water surface profile at 100% interception. This break in the inlet performance is consistent with an analysis reported by Izzard (1977) that introduced a characteristic length scale L2 (based on Froude Number effects) beyond which the interception capacity of the curb inlet significantly drops. This issue has potential safety implications as the gutter bypass and spread for a design storm will be larger than expected for such inlets. Designers are advised to consider the length scale L2 as the longest practical inlet for which HEC-22 equations are valid.
Schalla, F.E., and M. Ashraf, (2016) “Analysis of Flush Structural Supports and Design Equations for TxDOT Curb Inlets” Center for Transportation Research Annual Symposium.
Hodges, B.R., F.E. Schalla, M. Ashraf, and M. Barrett, “Limitations of traditional equations for large curb inlets,” National Hydraulic Engineer Conference, Portland, Oregon, August 9-12, 2016.