Modelling of Urban Stormwater Drain with Orifice Flow in Series using SWMM

• Main Author: Merry Shi Ting, Tang
• Format: Thesis
• Language: English; English
• Published: N.A. 2025
• Subjects: TA Engineering (General). Civil engineering (General)
• Online Access: http://ir.unimas.my/id/eprint/48980/

Stormwater infrastructure requires modification to solve the urban flooding problem due to increasing stormwater runoff rate and volume in the urban areas. This study investigated an urban drain (0.5 m W x 0.5 m D x 170 m L) divided into compartments with orifice flow restrictors to detain stormwater, subjecting the drain to three drain slopes of 0%, 0.2%, and 0.4%. The orifices had diameters ranging from 0.1 m to 0.5 m. A design rainfall of 5 minutes with a 10-year ARI intensity and three historical rainfalls were selected for stormwater flow analyses. Two rows of 12-unit terrace houses with 4,227 m² land area were selected as the study area. Three interventions were designed, namely: Drain with Single-Orifice (Scenario 1), Double-Orifice (Scenario 2), and Triple-Orifice (Scenario 3). The research utilized SWMM version 5.0 to effectively simulate the unique characteristics of the three interventions, creating sub-models that allowed for a detailed evaluation of the flow conditions in the study area and the impacts of different slopes, orifice sizes, numbers of orifice at varied locations. Overall, the 0.2% slope for design rainfall had the highest peak flow at the downstream end, while the 0% and 0.4% slopes peaked at the upstream end; for historical rainfall, the highest peak flow occurred at the downstream end for the 0% and 0.4% slopes, with the 0.4% slope also showing the highest peak flow upstream. However, the peak water level for the 0.1 m diameter result was the highest and decreased with increasing orifice diameter from 0.2 m to 0.5 m. The results indicated that Scenario 3, featuring diameters from 0.3 m to 0.5 m at a 0.2% slope, demonstrated the best performance with consistent reductions in peak flow and water level hydrographs, and no overflow was predicted for this scenario.