United States Department of Transportation
i
Interception Capacity of Conventional Depressed Curb Inlets and Inlets with Channel Extension
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2018-09-01
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[PDF-5.79 MB]
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Edition:Final Report
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Abstract:This report presents the results of a project investigating the performance of the TxDOT PCO curb inlet for effects of flush supports and internal hydraulic controls. PCO inlets use flush supports for the top slab of inlets longer than 5 ft, which are thought to reduce the interception capacity of curb inlets by as much as 50%. PCO inlets longer than 5 ft are divided into a main bay and side extension chamber(s). Unlike a conventional inlet, flow in an extension does not fall directly into a large bay. Instead, an extension has a channel directing the flow into the main bay, which has the potential to reduce the interception capacity. Three topics were investigated: 1) The effect of structural slab supports on the performance of curb inlets, 2) the performance of conventional depressed inlets under different flow conditions and road slopes, and 3) the effect of potential flow restrictions on the interception capacity of curb inlets with channel extensions. An existing model of a roadway with adjustable slopes was modified to accommodate a full-scale model of the depressed PCO inlet. Experiments for on-grade 10 and 15 ft inlets showed no observable difference in the intercepted flow due to the presence of slab supports. However, tests showed the present on-grade equations for long curb inlets significantly overestimate their capacity. A correction factor was developed for computing the 100% interception flow and a new relationship for computing the inlet capture at less than 100% interception condition. Tests showed the 10 ft PCO inlets on-grade are equivalent to a conventional inlet and requires the same correction factor to compute capacity. The 15 ft PCO inlets should never be used on-grade due to clogging potential. Tests for a submerged PCO extension in a sag show significant degradation such that 10 ft and 15 ft inlets will be 58% and 47% of expected capacity. PCO inlets are not recommended to handle submerged sag conditions
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