Land use change and its consequences for sewer infrastructure resilience in Al-Hussein neighborhood, Karbala, Iraq

The increasing pressures on the hydraulic stability of old sewer systems in cities with dense ageing densification due to rapid change in urban land use, which is turning residential to high-density commercial development, represent an increasingly dangerous outcome of urban-wildland interface zones. This paper explores a cumulative effect of a progressive land use change on the sewer network functioning of the Al-Hussein area in Karbala, Iraq, through applying a scenario-based Storm Water Management Model (SWMM). Four temporal land use scenarios were realistically simulated corresponding to the following 4 years of imperviousness on sub-catchments of 45%, 55%, 65%, and 75% based on the years 2005, 2015, 2025, and 2035, respectively, in four rainfall periods: a design storm (12.208 mm) and 2-year (24.667 mm), 5-year (36.789 mm), and 10-year (44.812 mm) events. The model was calibrated and validated against field observations with excellent statistical performance (NSE = 0.997–0.998, R 2 = 0.998–0.999, PBIAS = − 0.29–0.65%). Findings indicate a non-linear and accelerating decline in network resilience over increased imperviousness: Total storm volume under the design storm rose 26.8-fold between 59 m 3 in 2005 and 1580 m 3 in 2035, and 10-year storm volume rose 3051 m 3 to 20,583 m 3 , with flooded man The sensitivity and elasticity tests have determined land use change as the most significant driver of flooding, impacting flood amplification 6.9 times more significantly than the same amount of increase in rainfall intensity, and the effect of flooding on imperviousness has always been greater than 4.0 in all simulated conditions. The hydraulic critical threshold defined was at a 65% imperviousness threshold, where the spatial flood footprint would be growing exponentially and the network would be near system failure. The results will have a quantitative foundation to support the prioritization of land-use management, green infrastructure development, and selected pipe rehabilitation as supporting strategies to maintain the sustainability of sewer networks under sustained urbanization control.