Development of hydrologic simulation model to predict flood runoff in a small mountainous watershed

Most Korean watersheds are mountainous consisting of various soil types and land uses, and seldom watersheds are found to have long term hydrologic records. The SNUA, a hydrologic watershed model was developed to meet the unique characteristics of Korean watershed and simulate the storm hydrographs from a small mountainous watershed. The applicability of the model was tested by comparing the simulated storm hydrographs and those observed from Dochuk watershed, Gwangjugun, Kyunggido. The model includes the simulation of interception, evaporation and infiltration for land surface hydrologic cycle on the single storm basis and the flow routing features for both overland and channel systems. Net rainfall is estimated from the continuous computation of water balance at the surface of interception storage accounting for the rainfall intensities and the evaporation losses at each time step. Excess rainfall is calculated by the abstraction of infiltration loss estimated by the Green and Ampt Model from the net rainfall. A momentum equation in the form of kinematic wave representation is solved by the finite differential method to obtain the runoff rate at the exit of the watershed. The developed SNUA Model is a type of distributed and event model that considers the spatial distribution of the watershed parameters and simulates the hydrograph on a single storm basis. The results of verification test show that the simulated peak flows agree with the observed data in the occurrence time but have relative errors in the range of 5.4-40.6% in various flow rates and also show that the simulated total runoff have 6.9-32% of relative errors against the observed data. To improve the applicability of the model, it was thought that more studies like the application test to other watersheds of various types or the addition of other hydrologic components describing subsurface storages are needed