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M.a. Abdullahi, J. Abedi Koupai, M.m Matinzadeh,
Volume 28, Issue 3 (10-2024)
Abstract

Today, the problems related to floods and inundation have increased, particularly in urban areas due to climate change, global warming, and the change in precipitation from snow to rain. Therefore, there has also been an increasing focus on rainfall-runoff simulation models to manage, reduce, and solve these problems. This research utilized SewerGEMS software to explore different scenarios to evaluate the model's performance based on the number of sub-basins (2 and 8) and return periods (2 and 5 years). Additionally, four methods of calculating concentration time (SCSlag, Kirpich, Bransby Williams, and Carter) were compared to simulate flood hydrographs in Shahrekord city. The results indicated that increasing the return period from 2 to 5 years leads to an increase in peak discharge in all scenarios. Furthermore, based on the calculated continuity error, the Kirpich method is preferred to estimate the concentration-time in scenarios with more sub-basins and smaller areas. For the 2-year return period, a continuity error of 4% was calculated for the scenario with 2 sub-basins, while for the 5-year return period, the continuity error was 19%. On the other hand, the SCSlag method is preferred to estimate the concentration-time in scenarios with fewer sub-basins and larger areas. For the scenario with 8 sub-basins, a continuity error of 16% was calculated for the 2-year return period, and 11% for the 5-year return period.

M. Ranjbari Hajiabadi, J. Abedi Koupai, M.m. Matinzadeh,
Volume 28, Issue 4 (2-2025)
Abstract

Urban runoff is a serious issue due to urbanization and climate change. Therefore, paying attention to rainfall-runoff simulation models is important to manage and reduce adverse consequences. In this research, the performance of the SewerGEMS software was examined by studying different modes based on the number and area of sub-basins. Two modes, consisting of nine and seventeen sub-basins, were evaluated with varying durations of rainfall of 6 and 12 hours. Additionally, the performance of three methods for calculating concentration time (Kerpich, Brnsby-Williams, Carter) was compared to simulate flood hydrographs in Minab City. The results showed that the total volume of produced runoff in the nine sub-basins was 4% higher than in the seventeen sub-basins. The maximum runoff peak flow in the nine sub-basins was also 20% higher than in the seventeen sub-basins. Furthermore, the Brnsby-Williams method exhibited the least software continuity error among the three calculation methods for concentration time. On the other hand, the Carter method had the highest continuity error. The concentration time calculated by this method in some sub-basins exceeded the 6-hour duration of rain. A t-test was performed to compare the peak discharge data obtained from the Kerpich and Barnesby-Williams methods. The results indicated a significant difference between the data from the two methods at a 95% confidence level (p<0.05). Considering that the Kerpich method is suitable for calculating concentration time in small basins, it was used to compare the nine and seventeen sub-basins. Based on the findings, it was observed that merging the sub-basins and reducing their number from seventeen to nine resulted in an increase in the total volume of produced runoff from approximately 123,839 cubic meters to 128,446 cubic meters, as well as an increase in the maximum peak flow of runoff from about 2.400 m3/s to 2.884 m3/s. This demonstrates an increase in both the total volume and maximum peak discharge of the runoff.


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