Subcritical Flow Over Various Weir Shapes

Submerged flow exists for any given structure when a change in flow depth downstream from the structure causes a change in flow depth upstream from the structure for any given constant value of discharge. The two flow depths, normally measured when submerged flow exists, consist of a depth upstream from the structure, which is used also for free flow conditions, and a depth of flow located any place downstream from the structure. The initial studies in which the submerged flow analysis was developed were made on flat-bottomed flumes (Hyatt, 1965; and Skogerboe, Walker, and Robinson, 1965). Later studies verified the method of analysis for Parshall flumes (Skogerboe, Hyatt, England, and John son, 1965; and Hyatt, Skogerboe, and Eggleston, 1966). Because of previous findings, it was felt this method of analyzing submerged flow could be applied to various types and kinds of weirs. Original development of the parameters and relationships which describe submerged flow came from a combination of dimensional analysis and empiricism. Further verification of the parameters developed in this manner are obtained by employing momentum relationships. Both approaches to the submerged flow problem are discussed in this report. Considerable effort and study has been expended on free and submerged flow weirs by other authors in previous years. For this reason the authors of this report went to the literature as a source of data. Various studies typifying a particular type of weir structure were investigated and the data selected from these studies were subjected to the submerged flow analysis developed by the authors. The data from these studies provide further verification of validity of the approach to the submerged flow problem made by the authors. Acknowledgement is given and appreciation expressed to those authors whose studies provided the data used in the analysis presented in this report. Although no investigation was made of a contracted weir, the authors feel that the submerged flow analysis as explained in this report would be just as valid for this type of structure