Accurate discharge gauging and controlled energy release are recurring requirements in irrigation, drainage and hydraulic control structures. Compound weirs serve both, yet the pairing of a Cipolletti notch with a rectangular crest has not been characterized. This study presents the first clear-water dimensionless characterization of this compound sharp-crested weir in two orientations: a Cipolletti base with a rectangular crest (Weir-1) and the inverted arrangement (Weir-2). Tests covered bed slopes 0 to 4° and upstream heads H1 in a 5.00 m × 0.30 m tilting flume, with calibrated instruments, triplicate readings and a stabilisation criterion. Discharge followed the velocity-area method with Pitot verification, and the governing dimensionless groups (H1/P, H1/L, Re, We, S) came from the Buckingham π theorem. Weir-1 gave a stable rating, Cd = 0.63 ± 0.06 (CoV = 9.8%, 95% CI 0.61 to 0.66), exceeding Weir-2 (Cd = 0.52, CoV = 9.6%) by 20.3% (Welch t = 5.60, p < 0.001). The Cd model (RMSE = 0.052, MAE = 0.042; Shapiro-Wilk p = 0.83; VIF = 1.01) and the energy-dissipation relation (R2 = 0.83) were validated. Downstream Frd reached 6.47 and 11.66. A hydraulic performance index ranked Weir-1 above Weir-2 (0.74 versus 0.66), recommending it for dependable gauging. In practical terms, the study delivers a validated and transferable rating for a novel compound geometry that measures discharge with the accuracy of a purpose-built single weir while retaining low-flow sensitivity, and it provides a quantitative decision framework, including a hydraulic performance index, for selecting between gauging-oriented and dissipation-oriented configurations in canals, drainage systems and small hydraulic control structures.