Extended Abstract
Introduction
Effective urban water management is a cornerstone of sustainable development and public safety in a rapidly changing global climate. The growing variability in weather patterns, characterized by longer dry spells punctuated by intense, short-duration storms, places unprecedented stress on city infrastructures. This is particularly true for cities in arid and semi-arid regions, where drainage systems were often designed based on outdated hydrological data and can no longer cope with current precipitation extremes. In recent years, the increase in the frequency of seasonal precipitation, especially in arid regions, and the improper design of flood collection networks in such areas have caused inundation of streets and residential areas and disruption of citizens' daily activities. In addition, flooding of urban streets in various locations has caused the spread of environmental pollution and health hazards, threatening human health. These problems have been observed in many urban basins in Iran in recent years. Addressing this dual threat of flooding and pollution requires a paradigm shift from simply disposing of stormwater to actively managing it as a valuable asset. Urban runoff can be harvested as a supplementary water resource. This approach, not only mitigates flood damage but also provides an alternative water source for non-potable uses, such as irrigation and industrial cooling, thereby reducing pressure on conventional water supplies. Therefore, designing and improving urban runoff collection networks to address the mentioned problems is an inevitable necessity and is of great importance. In this study, a runoff collection system in a semi-arid urban area has been simulated. In this case study, short-term but high-intensity rainfall, uneven temporal distribution of rainfall, and impermeable surfaces (e.g., asphalt and concrete) increase the risk of sudden runoff and further highlighted the need for careful design of runoff management infrastructure. The simulation's primary objective is to model the hydraulic performance of the existing network under extreme rainfall scenarios and to propose and test optimized design configurations that can enhance the system's capacity, reduce flood peaks, and facilitate the safe capture of runoff for subsequent use.
Materials and Methods
The city of Anbarabad located in the south of Kerman is one of the areas where heavy rains in different seasons cause urban flood events. This city has two distinct climatic conditions: hot semi-humid in the west and hot arid in the east. The highest precipitation occurs in winter and autumn. The area that will be studied is the urban district of Anbarabad with an area of 684 hectares. In this study, the runoff collection network of Anbarabad was analyzed and optimized hydraulically using the SWMM 5.2. The information required by the model includes meteorological data (rainfall pattern, rainfall duration, input hyetographs, and other rainfall characteristics, intensity-duration-frequency curves, design rainfall, etc.) and spatial data (urban road map, land use map, soil type map and topographic map) along with runoff statistics. To determine the design rainfall, intensity-duration-frequency (IDF) curves were extracted. Prior to this, a data homogeneity test was performed using the run test method on the monthly rainfall data of the reference rain gauge station for the statistical period 1390 to 1399, which was obtained from the Iranian Meteorological Organization. After the sub-basinization operations in ArcGIS 10.8, the outlet hydrograph of each hydrological unit of the urban basin was calculated for a 10-year return period and based on that, the peak inflow discharge to the runoff collection network was determined and at the end, the network was hydraulically improved.
Results and Discussion
A comprehensive hydrological and hydraulic analysis was conducted to evaluate the performance of an urban drainage network under extreme flood conditions. A comparison of outlet hydrographs before and after channels modification (for a 10-year return period flood) revealed an increase in the peak discharge. This rise is attributed to the enhanced conveyance capacity of the modified system, which now routes water more efficiently towards the outlet, thereby altering the flood peak characteristics. The simulations revealed that physiographic characteristics substantially affect the hydrological behavior of each sub-basin. Sub-basins with steeper slopes, larger impervious surface areas, and higher equivalent widths generated higher runoff volumes. This variability in response underscores the importance of considering spatial heterogeneity in watershed management plans. Hydraulic simulation results indicated that 49 out of 56 nodes in Anbarabad's flood collection network experienced flooding. Among these, 28 nodes recorded the longest flooding duration, and node J21 exhibited the highest flood volume. The identification of such critical nodes is essential for prioritizing rehabilitation efforts and allocating resources effectively. Furthermore, the hydraulic analysis revealed that the existing runoff collection network in Anbarabad was undersized for the flood event, causing numerous stormwater channels to exceed their design capacity. This systemic inadequacy is a common issue in many rapidly urbanizing areas where infrastructure development lags behind land-use changes. Finally, based on the observed results, the geometric dimensions of stormwater channels were modified to provide the necessary capacity for flood conveyance. This intervention successfully eliminated flooding in previously affected nodes, demonstrating the critical importance of evidence-based, calibrated engineering solutions in building urban flood resilience.
Conclusion
The ongoing process of urbanization represents one of the most significant human impacts on the natural hydrologic cycle. The change in land use from natural and agricultural covers (e.g., forest, pasture) to urbanized ones (e.g., residential, commercial, industrial) has significantly heightened the challenges associated with urban watershed management. These changes reduce infiltration and increase both the volume and velocity of surface runoff, overwhelming traditional drainage systems. In this paper, the simulation of the surface runoff collection network of Anbarabad city located in Kerman province was performed using the SWMM 5.2 model. This widely recognized model was selected for its robust capability in simulating dynamic runoff processes and complex hydraulic routing within urban drainage networks. The modeling results were presented in the form of tables and graphs including peak discharge, cumulative runoff volume and peak flood flow time for each urban hydrological unit. Also, variations in outlet discharge across different network sections were quantified, enabling identification of critical zones contributing significantly to runoff production. This spatial analysis is crucial for implementing cost-effective mitigation measures where they are most needed. Subsequently, hydraulic simulation of the network revealed specific nodes experiencing overload or flooding conditions. These hydraulic bottlenecks were carefully analyzed to understand the underlying causes of system failure during storm events. Then, the necessary corrections were made at these points and finally, a modified surface runoff collection network was proposed that can effectively prevent runoff and improve the safety and welfare of citizens. The results obtained allowed the assessment of the contribution of each region to runoff production and the identification of priority areas for the implementation of surface runoff collection systems. This methodology provides a scientifically grounded framework for urban planners to enhance flood resilience in rapidly developing cities, particularly in water-scarce regions like Kerman province. |
