The simple equation of GIUH are frequently used in many researches instead of the derived equation of GIUH. However it is still unknown whether the simple equation of GIUH is adaptable for estimating IUHs for basins with various geomorphologic conditions. To verify the applicability of the simple equation of GIUH, in this research, four basins which were Bangrim, Sanganmi, Museong, and Byeongcheon were selected and each basin was assumed as the third and fourth stream order basin according to variable resolutions. After than, IUHs were estimated using the derived and simple equations of GIUH. Eight to sixteen hydrographs were estimated from the each IUH, compared with observed graphs. In case of that the basin is assumed as a third order stream, the derived equation underestimated the peak flows while the simple equation overestimated them. When the basin is assumed as a fourth order stream, the simple equation generally overestimated the peak flows whereas the derived equation produced peak flows good agreement with the observed peak flow.Moreover, the simple equation showed various deviations in accuracy whereas the derived equation produced stable results. Based on the fact found from this research, it can be concluded that the derived equation of GIUH brings better results than the simple equation of GIUH to estimate IUHs for ungauged basins.

This study is to derive the fourth-order Geomorphologic Instantaneous Unit Hydrograph (GIUH), driven for only third-order basin, for the application of GIUH to various types of basin. The second, third, and fourth order GIUHs were compared for various topographical conditions. The results showed lower peak runoff and later peak time in GIUH with higher stream order. Initial state probability was estimated from a function of geomorphologic parameters such as area ratio and bifurcation ratio for the application of GIUH. However, initial state probabilities and early parts of the GIUHs have negative values for many basins due to the inherent errors in the parameters. Initial state probability was calculated by area ratio of direct drainage using ArcView GIS 3.2 model to solve the problem.GIUHs were estimated for three basins, Sanganmi, Byeongcheon, and Sangye, using the above suggested method, and the results showed that the method is free of the problem.

There are various methods for the rainfall time distribution and numerous theoretical approaches have been proposed in many countries. The fact, however, is that only used model in each country are presented as official guidelines. In Korea, the Huff's method is generally used, but several problems have been proposed. Therefore, in this study, we developed the time distribution method using actual rainfall and verify its applicability. It is very reasonable to utilize the time distribution pattern which reflects the regional rainfall characteristics for designing the structures. In this study, a total of 172,851 storm events were extracted from 69 meteorological stations, and the hourly maximum rainfall over 30mm was separated to analyze the each event. Considering actual rainfall characteristic to drive the time distribution, we suggested the conditions and constraints to distribute the rainfall. Additionally, the constraint time distribution method can be applied to cases where peak runoff and runoff volume are crucial.

The phenomenon and impact of abnormal weather caused by climate change is not limited domestically, and the frequency and magnitude of natural disasters are increasing. In Korea, heavy rainfall has occurred, and sea level rise is accelerating. This falls under domestic urban disasters, which cause severe damage due to multiple floods in the coastal cities. In this study, the risk of disaster in the coastal cities was examined using XP-SWMM. In order to tackle the risk of flooding due to sea level rise, we examined whether the performance targets for the prevention of disasters were appropriate. Performance targets for the prevention of disasters and various scenarios of sea level rise were applied to the urban drainage system in Changwon City, where flood damage had occurred due to sea level rise. In spite of the freefall conditions for the currently set performance targets for the prevention of disasters, it was confirmed that there is a greater risk of flooding due to sea level rise. The results of this study show the spatial variation of flood risk due to sea level change near the coastal cities. Furthermore, these results can be used as reference data for establishing countermeasures to tackle related disasters.