This paper compares the risk of dam overtopping of two rolled compacted concrete (RCC) dams in Malaysia. Uniform methodology was carried out by selecting an appropriate probable maximum precipitation (PMP) series, performing a catchment PMP/PMF (probable maximum flood) rainfall runoff routing and finally, routing the inflow hydrographs through the reservoir water body. The critical PMP/PMF reservoir outflows and their corresponding flood rises were also compared. Both dams are considered safe using the current PMP series. The roles of surcharging volumes above the top water level of the reservoir were also demonstrated via their respective flow attenuation capabilities by their surcharging volume. This paper also demonstrates a close relationship can be forged between the product of spillway width and headroom vis-à-vis the catchment areas draining at the dam sites. The product represents a trade-off between a larger spillway vis-à-vis lower headroom, vice versa. Both Kinta and Bengoh dams’ spillway factors are consistently higher than the regressed curve using a vast database of existing dams and reservoirs in Malaysia.
Keywords: rolled compacted concrete, RCC, probable maximum precipitation, PMP, probable maximum flood, PMF, spillway: dam, flood design, Malaysia