Abstract. Laboratory data obtained from the overtopping failure of eight cohesive embankments built with different construction parameters are presented in this paper. Experiments were performed in two phases. Five experiments under phase 1 were carried out in small width flume having dimension viz. 17 m long, 0.6 m wide and 0.6 m high. In phase 2, three experiments were performed on large width flume having dimensions viz. 13 m long, 1.75 m wide and 0.5 m high. The construction parameters which were varied in embankments are compaction effort, compaction moisture content, and the moisture content at the time of failure. Phase 1 investigate the effect of compaction effort and compaction moisture content on breach parameters. As the water content of clay decreases or increases, the soil shrinks or swells which can cause damage ranging from small hairline cracks to severe structural distress. The sudden rise of water level in the reservoir due to heavy rain will cause rushing of water through cracks and if water overtopped the embankment will lead to quick failure. An attempt was made in phase 2 to investigate the effects on breach evolution when the embankments were air dried to reduce its moisture content and to develop cracks. The final breach shape and parameters noted in experiments show remarkable change for each dam failure. In the remainder of this paper, we report results of a set of small and large scale dam-overtopping experiments that were designed to; (1) investigate the effect of changing compaction effort and moisture content of the headcut migration, breach parameters, and flood hydrograph; (2) assess the overtopping behaviour of embankments when they are air dried for a long time.