Damage to Karnafuli Dam Spillway

Damage to the spillway chute occurred within three months of initial operation. A model study was commissioned to aid in determining the actual cause and sequence of events leading up to the failure. The model indicated that the vertical force acting on the concrete slab at the toe of the hydraulic jump was barely sufficient to hold that portion of the slab in place at the lower discharges; this of course omitted the effect of pressure fluctuations and surges characteristic of the prototype and applied only to symmetrical operation of the spillway gates. The factor of safety proved insufficient for the prototype. The paper also shows in perspective what can be expected from educators, under varying conditions of operation, when the underdrainage system terminates in the chute blocks of the stilling basin.