Texas Tech University

Project 0-5823

Hydraulic Performance Evaluation of Horizontal Inlet Type-H


Type H Inlets are frequently used by the Texas Department of Transportation as median drains for divided highways. Despite frequent use, engineers do not have adequate design information to mathematically describe the hydraulic performance of these structures. Typically, it has been assumed that IL-H-G and IL-H-L function essentially the same as road-way grates or curb inlets, but there is no basis for that assumption. Type-H drop inlets were investigated using a database from literature-reported experiments for similar inlets and physical model studies conducted at Texas Tech University. The findings of this study are: Type-H inlets, as studied, perform similar to the HEC-22 expectations when the weir-type conditions are applied (Equation (4-26) in HEC-22). Orifice-type models could not explain the TTU or the literature-derived observations. A power-law model that uses the dimensionless groups suggested by Cassidy (1966), with the slopes omitted, provides a reasonable explanation of inlet behavior. SWMM was investigated as a predictive tool by comparison to the TTU experimental results. The SWMM model was subject to very minimal calibration yet predicted performance reasonably well, especially when full inlet capture may occur.


Center for Multidisciplinary Research in Transportation (TechMRT)