## 2 Materials and Methods
### Model Conceptualization and Parameter Setup  
This study used the Computation Hydraulics International (CHI)'s PCSWMM model version 7.3.3095 with the SWMMS hydrology and hydraulics engine, which is based on the 1-D Saint-Venant equations as follows:  
\[\frac{\partial A}{\partial t}+\frac{\partial Q}{\partial x}=0 \tag{1}\]  
\[\frac{\partial Q}{\partial t}+\frac{\partial}{\partial x}\bigg{(}\frac{Q^{2}} {A}\bigg{)}+gA\frac{\partial H}{\partial x}+gAS_{f}+gAh_{L}=0 \tag{2}\]  
where \(Q\), \(H\), and \(A\) denote the flow rate, hydraulic head, and cross-sectional area, respectively; \(g\) is the gravitational acceleration; \(S_{f}\) is the friction slope; and \(h_{L}\) is the local energy loss per unit length. The continuity and momentum equations (as shown in Equations (1) and (2), respectively) were solved by the finite difference method with successive approximations [38]. Integrated hydrology-hydraulic modeling was carried out to simulate different urban flooding scenarios in the Damansara catchment. Two modules in PCSWMM: rainfall-runoff and flow routing process models, were selected for hydrological and hydraulic modeling, respectively. Figure 2 shows the parameters required for a PCSWMM model. Four input layers, including the sub-catchments, junctions, conduits, and outfalls, play an essential role in the flood simulations. The study area was first divided into sub-catchments using the catchment delineation tool in PCSWMM. For hydrologic analysis, each sub-catchment was assigned with the hydrology input parameters, such as area, flow length, slope, and imperviousness (Tables A1 and A2). The impervious percentage for the sub-catchments was taken from the guideline for Urban Stormwater Management Manual for Malaysia (MSMA 2 nd Edition) [39], which is in correspondence with the type of land uses. In this study, the Horton infiltration method introduced by [PERSON] [40] was selected, where surface runoff occurs once the rainfall intensities exceed the soil's infiltration capacity. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**Rainfall** & **Water Level** & **Station No.** & **Station Name** & **Latitude** & **Longitude** & **Standard** & **Skewness** & **Kurtosis** & **Maximum Rainfall** \\ \hline
3010001 & - & Kampung & 03°09′′29′′ & 101°32′04′′ & 14.05 & 3.23 & 13.41 & 134.50 \\  & - & Rumah Pam & 03°07′51′′ & 101°31′59′′ & 13.40 & 3.63 & 18.71 & 171.40 \\
3015085 & - & Tugu Keris Klang & 03°03′29′′ & 101°30′59′′ & 12.44 & 3.79 & 18.36 & 116.60 \\
3115079 & - & Puset Penyelikian Geath & 03°10′02′′ & 101°33′35′′ & 14.67 & 2.84 & 9.57 & 113.50 \\
3115081 & 3015490 & TIDI Jaya & 03°06′18′′ & 101°33′49′′ & 15.42 & 3.20 & 12.79 & 143.50 \\
3115082 & - & Kota Damansara & 03°09′39′′ & 101°34′59′′ & 15.22 & 2.92 & 10.04 & 123.40 \\ \hline \hline \end{tabular} Note: Standard deviation and maximum rainfall are in mm.  
\end{table} 
Table 2: Summary statistics of daily recorded rainfall series in Damansara catchment (2009–2019). The runoff generated from each sub-catchment subsequently enters a junction, usually a manhole structure, exits through a single conduit, representing any water conveyance channel, and finally flows into an outfall point. This process is referred to as hydraulic simulations, in which the dynamic wave method was used in the flood routing model. The required parameters of the rim (surface) and invert elevations for each junction and outfall were assigned based on the Digital Elevation Model (DEM) data, which can be obtained from the United States Geological Survey (USGS) EarthExplorer website ([[http://earthexplorer.usgs.gov/](http://earthexplorer.usgs.gov/)]([http://earthexplorer.usgs.gov/](http://earthexplorer.usgs.gov/)) (accessed on 7 July 2020)). In the simulation model, junctions and outfalls were connected via conduits (e.g., river or drain in this study). According to MSMA 2 nd Edition in 2012 [39], the Manning roughness coefficient for rivers and concreti-lined drains (with a rough finish) were determined as 0.035 and 0.018, respectively.