Urbanized areas are accompanied by increase in impervious areas such as construction of drainage systems, roads, roofs, destruction of soils structure, and destruction of vegetation due to growth urban area (Hsu, Chen, and Chang 2000; Hung, James, and Hodgson 2018; Kamali, Delkash, and Tajrishy 2017; Shuster et al. 2005; Sillanpää and Koivusalo 2015). This results in increased water pollution, hydrocarbons, heavy metals, pathogens and nutrients (Phillips et al. 2018; Pitt and Jr 2001; Qin, He, and Fu 2016). Complexities in the drainage infrastructures and urban areas have a natural influence on surface runoff that this runoff causes urban inundating (Chen, Hill, and Urbano 2009; Jamali et al. 2018). Urban inundation due to any kind of inefficiency or defect of urban drainage systems causes considerable damage in buildings and other private and public infrastructure and is among destructive and the common natural hazards (W. Chen et al. 2018; Hammond et al. 2015; Price and Vojinovic 2008; Tingsanchali 2012). Moreover, urban inundation can completely hinder or limit the traffic systems function, and loss of communications and business opportunities is among its indirect consequences. Urban inundation hazard is associated with the physical characteristics of inundation such as extension of inundation, water level above street, volume of water flowing and its duration(Zhu et al. 2016).
In recent years, some researchers have attempted to establish a more accurate relationship between rainfall – runoff and urban inundation (Bates, Horritt, and Fewtrell 2010; Lee 2018; Li, Chen, and Mao 2009; Radice et al. 2017). Various hydrological and hydraulic models have significant contribution to achieve this goal such as MIKE FLOOD (Löwe et al. 2017), ESTRYTUFLOW (Fewtrell et al. 2011), BREZO (Adeogun, Daramola, and Pathirana 2015), SWM (Yu, Huang, and Wu 2015) and InfoWorks ICM (Russo et al. 2015). Though, most of these models isn’t free, which limits their application. The storm water management model (SWMM), is open-source model and powerful tool to urban drainage analysis, which was developed from 1969 to 1971 by the EPA (Rossman 2004) has been used by researchers in various urban areas (Elliott and Trowsdale 2007; Rossman 2010) and coupled with other models, such as LISFLOOD-FP (Wu et al., 2017) and BreZo (Burns et al., 2015), to simulate urban inundation (Babaei, Ghazavi, and Erfanian 2018; L. Chen et al. 2018; Elliott and Trowsdale 2007). HEC-RAS is a tow-dimensional (2D) model that developed by Hydrologic Engineering Center (HEC) (Staff 2008) is one of the most popular model can coupled with SWMM model. HEC-RAS can simulate both unsteady and steady state flow conditions, and it can be used to calculate inundation areas. HEC-Geo RAS (GIS-based) were also used for accurate optimization of the geometry characteristics for real visualization of flood areas. The HEC-RAS model is frequently used in a river flooding study (Adams III, Chen, and Dymond 2018; Gao et al. 2018; Sleiman 2018), but in the present study, we used and evaluated the HEC-RAS and HEC-Geo RAS extension of ArcGIS10.2 to simulate inundation extents in street and its surface drainage. This hydrological and hydraulic coupled models does not require specific knowledge, nor does it on any commercial modules. Developing hydrological and hydraulic models that provide accurate estimates of urban inundation hazards are important to describe the best strategies for inundation risk mitigation (Ballesteros et al. 2011; de Kok and Grossmann 2010).
Combination of various factors affecting inundation and determination of the priority of their importance require an in-depth study. Therefore, to obtain accurate results, we need a powerful method to consider all factors in terms of their importance and study of the relationships between factors. Multi criteria decision analysis (MCDA) offers techniques and methodology to analyze decision problems, and it has been acknowledged as an important method in environmental decisions. The use of MCDA and GIS has been proven successful in studies on natural hazards. Analytic Hierarchy Process (AHP) is one of the most generally used methods to solve MCDA (Sleiman 2018) problems and is widely used for suitability analysis and natural hazard (Kokangül, Polat, and Dağsuyu 2017; Luu, Von Meding, and Kanjanabootra 2018; Papaioannou, Vasiliades, and Loukas 2015).
The specific objectives of this study are to (1) calibrate and validate the SWMM model to urban rainfall-runoff simulation (2) assess the capability of integrating the SWMM model with the HECRAS model for inundation zone mapping (3) provide an urban inundation hazard mapping using AHP with GIS support. The importance of the study is to provide remarkable information of the inundation depth to reduce environmental hazards of the areas at inundation risk so that it can be given as an input for local planning and decreasing the risk to property, people and the environment.
Urban areas have been generally considered as a data-scarce region due to the lack of hydrological gauges and hydraulic information. The novelty of this study lies in comparing the results of a hydrological model (Storm Water Management Model; SWMM) with a knowledge-based method (Analytic Hierarchy Process, AHP) that help decision-makers for urban flood management, especially in developing countries.