Simulation of the urban drainage system of Itanagar township using the Storm Water Management Model 5.2 (SWMM 5.2)

Abstract The existing drainage network of C Sector, Itanagar (Arunachal Pradesh, India), was analysed using the Storm Water Management Model version 5.2 (SWMM 5.2), a dynamic rainfall–runoff simulation model developed by the United States Environmental Protection Agency for the analysis, design and management of urban stormwater drainage systems. Daily rainfall data for the period 1986–2022 were obtained from the India Meteorological Department, Pune, and intensity–duration–frequency (IDF) curves were developed by Gumbel's method for return periods of 5, 10, 30, 50 and 100 years. The model simulates the hydrological and hydraulic processes within the urban catchment, including surface runoff generation and flow routing through the drainage network. The results show that the number of flooding nodes increases with increasing rainfall intensity: no node floods for the 5-year return period, whereas 2, 3, 6 and 7 nodes flood for the 10-, 30-, 50- and 100-year return periods respectively, with the total flood volume rising from 2.278 × 10⁶ to 15.683 × 10⁶ L. Two low impact development (LID) measures, namely rain barrels and permeable pavements, and their combination were then implemented to quantify their effect on runoff and flooding. Rain barrels reduced the total flood volume by up to 67.38% and permeable pavements by up to 32.84%, while the combined LID eliminated node flooding entirely for the 5- and 10-year return periods. The effectiveness of LID decreased as the return period increased. The study is useful for assessing future floods and for reducing the likelihood of urban flooding in hilly townships of the Eastern Himalaya.