This study dealt with risk-based analysis for design of concrete channel and grass-swale at Lima Kedai, Skudai, Johor. Recent trends in the design of channel and other structures are towards the use of risk analysis. The risk value for both concrete channel and grass-swale was evaluated using mathematical models in this study. The peak flow obtained using Rational Method for grassed swale and concrete with trapezoidal channel were 7.584 m3/s and 10.4 m3/s respectively. The drainage sizes (trapezoidal) for grassed swale was larger compared to concrete channel. The dimension for grassed swale was 1.6 meter (base width), 0.6 meter (depth) and 6.4 meter (surface width). Concrete channel size was 1.25 meter (base width), 0.5 meter (depth) and 5.25 meter (surface width). Overflow risk varies with elapse time (time to peak), whereby grassed swale has lower risk at lower drain time (recession time) and increased with increasing the drain time. The lowest overflow risk obtained were 0.207 (MASMA) and 0.250 (Rapid disposal). The overflow risk for highest elapse and drain time was 0.456 for grassed swale and 0.453 for rapid disposal (concrete). It is suggested to design at lower elapse and drain time to minimize the overflow risk.