Flood stage analysis considering the uncertainty of roughness coefficients and discharge for Cheongmi watershed

Abstract. The objective of this study was to analyze the flood stage considering the uncertainty caused by the river roughness coefficients and discharge. The methodology of this study involved the generalized likelihood uncertainty estimation (GLUE) to quantify the uncertainty bounds applying three different storm events. The uncertainty range of the roughness was 0.025 ∼ 0.040. In case of discharge, the uncertainty stemmed from parameters in stage-discharge rating curve. Parameters in rating curve were optimized by non-linear regression model and assumed by t-distribution. The range of parameters in rating curve was 5.138 ∼ 18.442 for A, -0.524 ∼ 0.104 for B and 2.427 ∼ 2.924 for C. By sampling 10,000 parameter sets, Monte Carlo simulations were performed. The simulated stage value was represented by 90% confidence interval. In storm event 1 ∼ 3, the average bound was 0.35 m, 0.74 m and 0.86 m, respectively. The peak bound was 0.49 m, 1.23 m and 1.61 m, respectively. The recurrence year of each storm event applying the frequency analysis was 1-year, 10-year and 25-year, respectively.