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2 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS Data-preparation form: Exp~ form 44-19 Rev.. Stage-Discharge Relationships at Culverts. COMPUTER PROGRAM The program is written in Fortran IV for the IBM 360/65 computer. Discharge coef- ficients and adjustment factors to be selected for the computations are as defined in II Meas- urement of Peak Discharge at Culverts by Indirect Methods, "'by G. L. Bodhaine (1968). The program is adapted from one originally written by W. P. Somers and G. I. Selner in Balgol language for use on the Burroughs 220 computer. Subsequent translation to Fortran IV. revisions, and updating were provided by J. V. Tanida, O. G. Lara, and H. E. Stull. Entries may be made on single computer input form for up to 12 selected discharges. up to 10 tailwater elevations. and up to 25 ground elevations in the approach cross sec- tion. The approach cross section can have up to four subareas with independent rough- ness coefficients~ The computer can vary the roughness coefficients with depth by in- terpolation between assigned values at se- lected elevations. An approach section is required for every computation; therefore, if ponded approach conditions are anticipated and no cross section was obtained, a simple shape is assumed for which stationing and ground elevations are estimated in the field. The program can accommodate single- barreled circular pipes, riveted or multi- plate pipe- arches, and rectangular box cul- verts having either no webs, or up to nine webs. It handles three entrance geometries directly: (a) flush setting in vertical head- wall, (b) wingwall entrance, and (c) project- ing entrance. The section and hydraulic properties of the three types of culvert bar- rels are computed and the type of flow is de- termine.a. Unusual conditions, such as mi- tered pipes set flush with sloping embank- nlents, and culverts with 900 wingwalls, are discussed on page 14 in more detail. Because almost all discharge coefficients and adjustment factors are independent of discharge or velocity, the user determines the appropriate net coefficient for several headwater elevations. The coefficient for type 3 flow in rectangular box culverts is dependent on the Froude number; this coeffi- cient is therefore determined by the COln- puter. The user has full freedom in select- ing nearly all of the various discharge coef- ficiEmts and adjustments. Low- head now is separated from high- head flow by the manner in which computation equations are balanced. Sometimes if cri- teria within the program are not satisfied in the transition range, there may be no com- puted results for certain discharges. Under such circumstances graphical interpolations can be made through the transition range to complete the entire rating. When high-head conditions are computed, headwater elevations are generally given for both types 5 and 6 flow. The decision on the optimum figure is left to the analyst; guide- lines are offered by Bodhaine (1968). Sug. gested procedures are given for smoothing the rating curve in the transition from low- to high-head conditions. BASIC EQUATIONS AND COMPUTATION METHODS The program consists of three major parts: (1) a precomputation edit program; (2) computation of section properties and the critical discharge for selected elevations at the approach section, and culvert-barrel section properties; and (3) computation of headwater elevations for selected discharges and tail water elevations. Part 1 A precomputation edit program examines all the input data for errors in logic, for im- proper symbols, or for lack of agreement with physical limits set on some of the input parameters. The error messages are ex- plicit. Explanations of typical error mes- sages are given on pag.e 16. If a given culvert problem has no input errors, computation commences at once before the next culvert problem is examined for errors. When a fatal error is detected, a message identifying the particular culvert is first printed as follows, referring to the card 2 for that problem: THE LAST NUMBER 2 CARD READ WAS TITLED "_nnnn (see site