Hydraulic performance of pennsylvania highway drainage inlets (Type J, Type 4-Ft. Special, and Type 6-Ft. Special), November 1972

\ An experimental investigation of the performances of some highway drainage inlets is presented. The purpose of this study was to provide information to aid in the design of spacing highway drainage inlets. The channel considered was triangular in cross-section with one side having slopes ranging from 48:1 to 12:1. The other side or back slope had a slope of either 1/8:1 or 3:1. The drainage inlets studied were (1) Type J Inlet, (2) 4-Ft Special Inlet, and (3) 6-Ft Special Inlet. They are standard inlets used by the Pennsylvania Department of Transportation and are customarily installed in paved channels. Model inlets were built to half the scale of actual inlets. Each inlet was tested under a variety of channel configurations and with a certain range of channel flow rates. The capacity of an inlet was determined by actual measurements, and thus the efficiency of an inlet was obtained. A series of curves, relating efficiency to capacity for an inlet, are presented in the study. The curves show that as more water flows in the channel toward an inlet the efficiency of the inlet decreases. The knowledge obtained from this investigation provides information that is· more adequate to the designer in determining the spacing of highway drainage inlets than the information presently available.