In the last few decades tremendous progress has been made in the use of catchment models for the analysis and understanding of hydrologic systems. A common application involves the use of these models to predict flows at catchment outputs. However, the outputs predicted by these models are often deterministic because they focused only on the most probable forecast without an explicit estimate of the associated uncertainty. This paper uses Bayesian and Generalized Likelihood Uncertainty Estimation (GLUE) approaches to estimate uncertainty in catchment modelling parameter values and uncertainty in design flow estimates. Testing of join probability of both these estimates has been conducted for a monsoon catchment in Vietnam. The paper focuses on computational efficiency and the differences in results, regardless of the philosophies and mathematical rigor of both methods. It was found that the application of GLUE and Bayesian techniques resulted in parameter values that were statistically different. The design flood quantiles estimated by the GLUE method were less scattered than those resulting from the Bayesian approach when using a closer threshold value (1 standard deviation departed from the mean). More studies are required to evaluate the impact of threshold in GLUE on design flood estimation.2 of 15 applied the Bayesian inference to estimate rainfall uncertainty characterized by two parameters k and rMult for Abercrombie River's daily flow. Rainfall flood events were simulated as random processes (e.g., [1,[4][5][6][7][8][9]). The model parameter error and output error, in this case, were combined into a single random process.Model error: The model error is estimated mainly by analysis of model parameter uncertainty. A well-known approach in uncertainty analysis of model parameters is the behavioral approach [10,11]. Examples of this approach are as follows: Generalized Likelihood Uncertainty Estimation (GLUE) method [12][13][14]; Bayesian method using Metropolis-Hasting algorithm and Adaptive Metropolis (AM) algorithm [1,15,16]; and Markov chain Monte Carlo [17][18][19]. In this approach, the input and output errors are ignored and the threshold of objective functions for selecting parameter values were determined.Using the threshold to select parameter values was developed in the GLUE method, firstly introduced by Beven and Binley [12]. This procedure recognizes the equifinality of different sets of parameters in the generation of acceptable catchment response. The parameters producing acceptable responses are assigned "behavioural" and will be accepted [12]. Identifying the threshold in the GLUE method is based on an acceptable range of performance measures such as Nash-Sutcliffe Efficiency (E), Root Mean Square Errors, percent bias, and correlation coefficient (e.g., [20,21]. For example, in the hydrograph measure of fit using Nash-Sutcliffe Efficiency (E), the range of E was established. Cameron [21] and Zhao [20] selected threshold of 0.7, Shen [22] accepted the threshold of 0.5. In design flood quantile...