Storm-coverage effect on dynamic flood-frequency analysis: Empirical data analysis

In this study, a dynamic flood-frequency analysis model considering the storm coverage effect is proposed and applied to six sub-basins in the Pyungchang River basin, Korea. The model proposed is composed of the rectangular pulse Poisson process model for rainfall, the Soil Conservation Service curve number method for infiltration and the geomorphoclimatic instantaneous unit hydrograph for runoff estimation. Also, the model developed by Marco and Valdes is adopted for quantifying the storm-coverage characteristics. By comparing the results from the same model with and without the storm-coverage effect consideration, we could quantify the storm-coverage effect on the flood-frequency analysis. As a result of that, we found the storm-coverage effect was so significant that overestimation of the design flood was unavoidable without its consideration. This also becomes more serious for larger basins where the probability of complete storm coverage is quite low. However, for smaller basins, the limited number of rain gauges is found to hamper the proper quantification of the storm-coverage characteristics. Provided with a relationship curve between the basin size and the storm coverage (as in this study), this problem could be overcome with an acceptable accuracy level.