Document Type : Research Article
Authors
Department of Geomorphology, Faculty of Planning and Environmental Sciences, University of Tabriz, Tabriz, Iran
Abstract
On the northern and southern slopes of Tabriz, several small and large drainage basins direct their runoff toward the city. Urban expansion toward the outlets of these basins, together with extensive land‑use changes and modifications to natural watercourses in recent decades, has increased the risk of flooding. This study aimed to evaluate and prioritize the flood‑susceptibility potential of drainage basins draining into the metropolitan area of Tabriz using morphometric analyses and multi‑criteria decision‑making (MCDM) models. To this end, the morphometric characteristics of the northern and southern basins—including basin area, number of streams, drainage density, stream frequency, drainage texture, drainage intensity, circularity ratio, form factor, compactness coefficient, basin relief, and ruggedness number—were extracted using a Geographic Information System (GIS). The SWARA method was then applied to determine the weights of the criteria affecting flood susceptibility, followed by the MABAC model to rank the basins based on their flood‑susceptibility potential. The results revealed that among the northern basins, Basin N1 exhibited the highest flood susceptibility, with a final weight of 0.206. Similarly, among the southern basins, Basin S6 was identified as the most sensitive unit, with a weight of 0.366. These basins mainly owe their high flood‑susceptibility potential to larger area, high drainage density, and steep slopes.
Introduction
Several small and large drainage basins flow toward the city of Tabriz. The city’s expansion toward the outlets of these basins, along with extensive land‑use changes and the alteration of natural watercourses over recent decades, has increased the flood hazard. During precipitation events, these basins collect and convey rainfall-derived waters that manifest as surface runoff and ephemeral flows within the basins. Subsequently, following the steep and generally uniform topographic gradient of the slopes, these flows are directed downstream toward lower-lying areas and the urban extent of Tabriz. Meanwhile, the rapid and unregulated physical expansion of the Tabriz metropolis toward the outlets of these basins, together with the continuous intensification of construction activities—including residential and commercial buildings as well as transportation networks—within and across the corridors of secondary watercourses, and without adequate consideration of hydrological and geomorphological constraints in urban planning and design processes, has substantially increased the risk of various hydro-geomorphological hazards. These hazards include sudden and destructive flash floods as well as unstable slope movements in the affected areas.
Material and Methods
The study area of the present research comprises the basins toward the metropolitan area of Tabriz. Tabriz, the capital of East Azerbaijan Province, is located at geographical coordinate's 38° 02′– 38°10′ north latitude and 46° 11′ – 46° 23′ east longitude, with a mean elevation of approximately 1366 m above sea level. According to records from the synoptic meteorological station at Tabriz International Airport, the city’s mean annual precipitation during the period 1992–2024 is approximately 255 mm.
In the present study, a Digital Elevation Model (DEM) with a spatial resolution of 12.5 meters was employed to delineate the catchment areas of the region and to calculate their morphometric parameters. Subsequently, two different methods were employed for data analysis: (1) the MABAC model and (2) the SWARA model. The Multi-Attributive Border Approximation area Comparison (MABAC) method was introduced by Pamučar and Ćirović in 2015. This method is among the most recent multi-criteria decision-making (MCDM) techniques and is widely used for ranking alternatives. The SWARA model is applied as a multi-criteria decision-making technique to calculate the weights of criteria and sub-criteria.
Results and Discussion
In the present study, the morphometric characteristics of the northern and southern basins of Tabriz were analyzed, including parameters such as basin area, stream number, drainage density, stream frequency, drainage texture, drainage intensity, circularity ratio, form factor, compactness coefficient, relief, and ruggedness number. These parameters were extracted using a Geographic Information System (GIS). The research findings indicate that the morphometric characteristics of drainage basins play a decisive role in intensifying or mitigating flood susceptibility. In this regard, criteria such as basin area, stream density, and elevation were identified as the most influential factors affecting runoff generation and the occurrence of flash floods. The results obtained from the SWARA model for criteria weighting reveal that parameters related to basin size and shape (e.g., basin area, compactness coefficient, and circularity ratio), as well as drainage network characteristics (such as drainage density and stream number), contribute most significantly to increased flood susceptibility.
Conclusion
This study was conducted with the aim of assessing and prioritizing the flood susceptibility potential of basins into the metropolitan area of Tabriz, through the integration of morphometric analysis and the combined application of the MABAC and SWARA multi criteria decision making methods. Basin prioritization using the MABAC model indicated that Basin N1, located on the northern slopes of Tabriz, was identified as the most flood-prone basin, with the highest final weight (0.206). This basin, due to a combination of relatively large area, high drainage density, and considerable slope, provides favorable conditions for rapid runoff generation and an increased flood hazard. In contrast, basins with negative final weights (such as Basins 2 and 4 in the northern sector) exhibit lower flood susceptibility, which is mainly attributed to moderating morphological characteristics such as elongated basin shape and low drainage density. In the southern sector, Basin N6 ranked first with a final weight of 0.366. The predominance of this basin is primarily due to its larger area, significant elevation differences, and high drainage density, all of which are key factors contributing to increased runoff volume and flow velocity. These findings indicate that even in semi-arid climatic regions, the presence of large and steep mountainous basins can significantly intensify the risk of flash floods, particularly during wet seasons. From an applied perspective, the results of this research can serve as an effective tool for urban, environmental, and watershed managers and planners. The proposed prioritization facilitates the optimal allocation of resources and the implementation of both structural and non-structural measures—such as the construction of sediment retention dams, land-use pattern modification, conservation and restoration of vegetation cover, and the design of early warning systems—in high-risk basins. Particularly in light of the rapid and unregulated physical expansion of Tabriz toward the outlets of these basins, the incorporation of hydrological and geomorphological considerations into urban development plans and the enforcement of construction controls within stream buffer zones are increasingly imperative. In conclusion, this study confirms the effectiveness of integrating Geographic Information Systems (GIS), quantitative morphometric analyses, and multi-criteria decision-making methods in basin-scale natural hazard assessment. It is recommended that future studies enhance model accuracy and reliability by incorporating hydro climatic parameters (such as rainfall intensity and duration), anthropogenic factors (including land-use change and building density), and higher-resolution datasets. Such an approach would not only contribute to improved flood risk management in the metropolitan area of Tabriz but could also serve as a methodological framework for other cities located adjacent to mountainous drainage basins.
Acknowledgements
We are grateful to all the scientific consultants of this paper.
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