In urban areas, runoff flow is drained through sewer networks as well as surface areas. Therefore, it is very important to consider sewer
networks as a component of hydrological drainage processes when conducting urban inundation modelling. However, most researchers
who have implemented urban inundation/flood modelling, instinctively simplified the sewer networks without the appropriate criteria.
In this research, a 1D-2D fully coupled urban inundation model is applied to estimate the influence of sewer network simplification
on urban inundation modelling based on the dendritic network classification. The one-dimensional (1D) sewerage system analysis
model, which was introduced by Lee et al. (2017), is used to simulate inlet and overflow phenomena by interacting with surface flow.
Two-dimensional (2D) unstructured meshes are also applied to simulate surface flow and are combined with the 1D sewerage analysis
model. Sewer network pipes are simplified based on the dendritic network classification method, namely the second and third order, and
all cases of pipes are conducted as a control group. Each classified network case, including a control group, is evaluated through their
application to the 27 July 2011 extreme rainfall event, which caused severe inundation damages in the Sadang area in Seoul, South
Korea. All cases are compared together regarding inundation area, inflow discharge and overflow discharge. Finally, relevant criterion
for the simplification method is recommended.