Hydraulic Efficiency of Grate and Curb Inlets - Urban Drainage and ...

1 INTRODUCTION
A research program was conducted at Colorado State University (CSU) to evaluate the
hydraulic efficiency of three storm-drain inlets. Inlets tested in this study are currently used by
the Urban Drainage and Flood Control District (UDFCD) of Denver, and consist of the Denver
Type 13 and 16 grates, and the Colorado Department of Transportation (CDOT) Type R curb.
These inlets have never been specifically studied or tested for development of hydraulic
efficiency relationships. Current design practices are based upon a document produced by the
Federal Highway Administration (FHWA, 2001) titled “Hydraulic Engineering Circular 22”
(HEC 22). General inlet types are addressed in HEC 22, but no specific guidance is provided
for these three inlets used by the UDFCD. The study presented in this report focused on
collecting data on these inlets under physically-relevant design conditions, and developing
improved design methods for determining inlet efficiency under varying road geometries. A 1/3
Froude-scale model of a two-lane road section was designed and built at the Engineering
Research Center (ERC) of CSU. The model consisted of an adjustable slope road surface, gutter
panels, and three interchangeable inlet types positioned in a testing flume. Details pertaining to
model construction, testing procedure, resulting database, and data analysis are presented in this
report.
1.1 Project Background
Storm-water runoff is typically conveyed through a network comprised of streets, gutters,
inlets, storm sewer pipes, and treatment facilities. Streets of developed areas often serve as
collectors for runoff, and convey water into gutters and eventually to storm sewer inlets. Stormwater
management in the metropolitan Denver area falls under the jurisdiction of the UDFCD.
Policies, design procedures, and Best Management Practices (BMPs) are provided in the “Urban
Storm Drainage Criteria Manual” (USDCM; UDFCD, 2008). Design methods presented in the
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