FLOOD06423 - Laserfiche WebLink

Home Browse Search

PREPARATION OF INPUT DATA FOR AUTOMATIC COMPUTATION OF STAGE-DISCHARGE RELATIONS AT CULVERT~ By Howard F. Matthai, Harold E. Stull, and Jacob Davidian ABSTRACT Detailed instructions are given on the preparation of input data for automatic com- putation of stage-discharge relations at cul- verts. The program follows standardized methods of computing headwater elevations, given discharges, tail water elevations, and the geometries of the approach cross section and the culvert. The basic energy equations are programed for solutions for single- barreled circular pipes, riveted or multi- plate pipe-arches, and rectangular box cul- verts with or without webs. A full stage- discharge relationship can be developed for the range of discharges and tailwater elevations selected. A computation option that is independent of culvert dis- charge can be used to obtain section proper- ties either of a defined channel cross section, or of both' the approach cross section and of the culvert barrel. One example demon- strates the technique. INTRODUCTION For convenience in computation, culvert flow has been classified into six types on the hasis of the location of the control section and the relative heights of the headwater and tailwater elevations. The six types of flow are illustrated in figure 1. The procedures given by Bodhaine (1968) for computation of peak discharge at culverts have been adapted by R. W. Carter and W. P. Somers to com- pute headwater elevations at the approach section for given discharges and tailwater elevations. The output of the program is a headwater elevation for each selected dis- charge for ali automatically determined types of flow. A stage- discharge rel,ation- ship, or rating. can be plotted and tabulated from the output. A family of. curves is nec- essary for type 3 flow where tailwater ele- vation partially controls the headwater elevation, and a differential head-discharge relation is u sed for type 4 flow. The procedures are applicable to most sites where a culvert is used as a metering device. Peak discharges and runoff during floods are determined frequently at culverts where crest-stage gages or water-stage re- corders are installed. The full rating for the site can be obtained from a judicious selection of discharges and tail water ele- vation's. The peak discharge of an actual flood is determined by applying the elevation of high-water marks. preferably near the approach section. to the computed stage- discharge relation. If the gage is not at the approach section, the relation between the computed headwater elevation and the re- corded stage must be established. The prog~am may be used to compute cross- section properties without regard to the flow in the culvert provided there are no more than four subareas. The computation techniques and detailed instructions for the preparation of input data are explained in this manual. This manual is designed for use with pro- gram number A526. and data-preparation form 9-1695, Stage- Discharge Relations at Culverts. The manual, program number. and da~a-preparation form displace, respec- tively, their counterparts of an older program used heretofore: Somers, W. P., and Selner, G. I., 1965, Computation of stage-discharge relation- ships at culverts: Surface Water Tech- niques. hook 1, chap. R, If. S. CeoI. Survey report.. Program number: ^~31 (al:-;o known a:<; M0044).