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At Utah State University, considerable effort has been devoted to the analysis of submerged flow at open channel constrictions. A method of analyzing submerged flow was first developed for a trapezoidal flume by Hyatt (1965). Later studies verified the method of analysis for a rectangular flume (Skogerboe, Walker, and Robinson, 1965) and Parshall flumes (Skogerboe, Hyatt, England, and Johnson, 1965). Because of the previous findings, it was felt this method of analyzing submerged flow could be applied to highway embankments.

A highway embankment is a form of broad-crested weir when overtopped by flood waters. Being a weir, the flood discharge over the embankment is only a function of the upstream depth for free flow conditions. This report will present a method for determining the discharge under submerged flow conditions using the upstream and downstream depths. Thus, post flood field measurements and observations, when properly obtained, will provide the necessary information for an accurate determination of the flood discharge for either free or submerged flow conditions.

The concepts involved in the analysis of submerged flow at open channel constrictions were originally developed by dimensional analysis for flow measuring flumes. The parameters describing submerged flow in flumes have been further verified by the development of theoretical submerged flow equations which utilize momentum theory and energy relationships.

The experimental models studied by Kindsvater (1964) are comparable to a secondary highway embankment. The models were constructed to a scale of 1/9 a typical secondary roadway. The data resulting from the model studies has been subjected to the method of submerged flow analysis previously employed with flow measuring flumes. The consistency of the data, both fro free flow and submerged flow, reflects the quality of the experimental design and produces employed in collecting the data. Although the data presented in this report applies only various forms of secondary road embankments, the methods of analysis are general. The development of calibration curves for other embankment geometries requires only the generation of additional data employing model studies.