AbstractDue to the increasing stormwater runoff in urban areas, stormwater infrastructure requires modification to address the flash flooding issues. Occurrences of floodwater overflowing the urban drain have urged drainage engineers to re-look its design. Conventionally, the urban drain is designed to free flow following the provided drain slope. This paper is challenging the old design by introducing orifices into the drain. The lesser-known stormwater characteristics restricted by orifices in open drains were investigated. In this case, twenty-four units of terrace houses were selected as the study area with special attention to the 170 m front drain with a dimension of 0.5 m x 0.55 m. The drain was inserted with one to three orifices of 0.45 m diameter separating the drain into one or more compartments. Three scenarios were formulated, namely S1 with one orifice plate at 170 m, S2 with two orifice plates at 86 and 170 m, and S3 with three orifices at 50, 110 and 170 m, from the starting po.....