This paper explores the integration of stormwater simulations within the BIM site engineering process, using Swiss standards as a reference for test projects in Bangkok and Zürich. The study investigates whether combining BIM and hydrology/hydraulic software enhances workflow and provides more flexible decision support tools for landscape architecture projects. The methodology involves creating 2D CAD drawings and models in Civil 3D, followed by simulations using two different physically-based hydrologic/hydraulic models with the Rational Method option. Results show that the standard Civil 3D pipe networks require additional manhole sizes for smaller projects to reduce concrete use. The Swiss standard SN 592 000 serves as a valuable reference for projects globally, including regions with tropical climates. The research emphasizes the need for improved software tools that incorporate a wider range of pipe and manhole sizes with sustainable material options, as well as the value of applying more rigorous, conceptual hydrologic/hydraulic modeling approaches for complex design considerations, such as NbS/bioretention, pond/wetland storage, and water quality.