Urban development scenarios on flood peak discharge in an arid urban watershed using the WinTR-۵۵ hydrologic model

KGROUND AND OBJECTIVES: Land use change can directly affect rainfall-runoff relationships. The change in land use is an essential factor in runoff production. This research evaluated the effect of urban development scenarios of land use change on runoff in Gonabad city of Iran. The innovation and importance of this work are to determine which land use changes have the greatest impact on the flood discharge in this urban area. Also, determine how much the minimum development of urban green space is to control and reduce peak flood discharge in this city that is located in a dry area.METHODS: The effect of urban development scenarios on runoff was evaluated by the WinTR-۵۵ model in ۵ sub-basins of Gonabad city. The main data required for inputting to the WinTR-۵۵ model are sub-area and reach characteristics, curve number, and storm data. The storm data in TR-۵۵ are ۲۴-hour rainfall amounts in a return period of ۲, ۵, ۱۰, ۲۵, ۵۰, and ۱۰۰ years. The changes in the maximum flood discharge and flow hydrograph in each sub-area and return period were calculated by the WinTR-۵۵ model under existing land use conditions and ۹ scenarios of urban development.FINDINGS: The greatest increase in runoff production was related to the conversion of abandoned fallow and agricultural lands to residential. Also, the most effective increase or decrease of land cover change in peak flow discharge and total flow volume was at the ۲-year return period. The decreased effect of the development of green spaces and urban gardens on peak flow discharge and total flow volume was seen only if their development was more than ۵۰%. The average maximum decrease in peak discharge and total flow volume was ۲۲.۷% and ۱۶.۱%, respectively. While the average maximum increase in peak discharge and total flow volume was ۸۴.۴% and ۵۳.۹%, respectively.CONCLUSION: The effect of increasing green spaces and urban gardens on the reduction of peak discharge and volume of runoff was also evident in the study area. Land management and preventing the conversion of permeable land uses such as agricultural, gardening, fallow lands, and rangeland will be much simpler and less costly. Urban land use management to prevent urban floods requires the expansion of permeable surfaces, especially green spaces, and urban gardens. These are the important novelty of this research that can be beneficial for future urban developments of Gonabad city and its flood management activities.