Junction Loss Experiments: Laboratory Report Publication No. FHWA-HRT-07-036

The junction loss study described in this report was conducted at the Federal Highway
Administration (FHWA) hydraulics laboratory. Between 1986 and 1992, Chang et al. conducted a
lab study of energy losses through junction access holes, using relatively large-scale (one-quarter
scale) physical models.(1) A preliminary method for determining such losses, based on early results
from that study, was published in the Federal Highway Administration’s (FHWA) Urban Drainage
Design Manual (Hydraulic Engineering Circular No. 22 (HEC 22)).(2) FHWA plans to update HEC
22 and further develop computer software for storm drain design. The need for consistent
technology in FHWA publications and software applications on this subject is urgent. To
accommodate that need and overcome some of the difficulties in estimating energy loss in access
holes, the FHWA’s Office of Bridge Technology initiated this study to validate Roger Kilgore’s
proposed method for computing access hole energy losses. This report will be of interest to
hydraulic engineers involved in storm drain design and to researchers involved in developing
improved storm drain design guidelines. It is being published as a Web document only.
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