SELECTION AND INSTALLATION OF CUTTHROAT FLUMES FOR MEASURING IRRIGATION AND DRAINAGE WATER

THE CUTTHROAT FLUME HAS BEEN DEVELOPED FOR OPERATION UNDER BOTH FREE FLOW AND SUBMERGED FLOW CONDITIONS. THE FLUME HAS A FLAT BOTTOM. VERTICAL WALLS, AND A ZERO-LENGTH THROAT SECTION. THE MOST OBVIOUS ADVANTAGE OF A CUTTHROAT FLUME IS ECONOMY OF FABRICATION DUE TO THE FLAT BOTTOM AND ELIMINATION OF THE THROAT SECTION COMMON TO OTHER FLOW MEASURING FLUMES. ANOTHER ADVANTAGE IS THAT ALL FLUMES HAVE THE SAME CONVERGENCE AND DIVERGENCE RATIOS, THEREBY ALLOWING THE SAME FORMS OR PATTERNS TO BE USED FOR ANY THROAT WIDTH. THE USE OF A CONSISTENT GEOMETRIC SHAPE HAS FACILITATED THE DEVELOPMENT OF GENERALIZED FREE FLOW AND SUBMERGED DISCHARGE RELATIONS. ANY FLUME LENGTH BETWEEN 1.5 FEET AND 9 FEET CAN BE USED, WHILE THROAT WIDTHS BETWEEN 1 INCH AND 6 FEET HAVE BEEN INVESTIGATED. THE DIFFERENCES BETWEEN FREE FLOW AND SUBMERGED FLOW CONDITIONS ARE DISCUSSED AND THE NECESSARY CRITERIA FOR DETERMINING WHICH FLOW REGIME EXISTS ARE ESTABLISHED. THE TRANSITION SUBMERGENCES ARE GIVEN FOR THE RANGE OF FLUME SIZES INVESTIGATED. FOR FREE FLOW, THE RATIO OF INLET FLOW DEPTH TO FLUME LENGTH SHOULD PREFERABLY BE LESS THAN 0.4. THE ACCURACY OF DISCHARGE MEASUREMENT FOR SUBMERGED FLOW RAPIDLY DETERIORATES ABOVE SUBMERGENCES OF 95 PERCENT. EXAMPLES ARE GIVEN WHICH ILLUSTRATE THE DESIGN PROCEDURE FOR DETERMINING FLUME SIZE, AS WELL AS OBTAINING THE FREE FLOW AND SUBMERGED FLOW RATINGS. PROPER INSTALLATION AND MAINTENANCE PROCEDURES FOR CUTTHROAT FLUMES ARE DESCRIBED. /COLOSTU/