Components and design functions of straight drop spillways:
Statement (B) is correct: Transverse sills (end sills) placed across the stilling basin floor stabilize and force the formation of a hydraulic jump within the basin, effectively dissipating kinetic energy.
Statement (C) is correct: Longitudinal sills running parallel to the direction of flow prevent cross-currents and eddies, guiding and straightening discharge uniformly downstream.
Statement (A) is incorrect: Standard SCS criteria require straight reaches of typically 15 to 30 meters (not a rigid 50 m requirement).
Statement (D) is incorrect: Cutoff walls are designed to reduce (not increase!) seepage uplift pressure and eliminate piping failures beneath the structure.