Application of 2D drainage modeling has been very attractive in urban settings, especially in determining flood vulnerability of properties. The advantage of 2D modeling over 1D modeling is because it provides a better assessment of inundation of water in a complex terrain. With the increase in availability of high resolution DEMs, more accurate 2D modeling is becoming increasingly feasible.
This paper presents a case study of an evaluation of a frequently flooded commercial complex mainly due to the inadequacy of the minor drainage system of the site. The site was modelled separately with a 1D minor system and as a dual drainage system to compare the results. Surface flow in the site (major drainage system) was modeled using PCSWMM 2D. Hydrology for the 2D system was modeled considering each 2D cell as a subcatchment in comparison to 1D model which used much larger lumped subcatchments. 2D cells were connected to the minor system at the existing catchbasin locations using orifices. The combined model was run with different options for 2D-1D connection using side and bottom orifices and also with different orifice dimensions to simulate inlet conditions at the catchbasin grates.
2D depiction of the dual drainage system allowed to simulate the hydraulics at the site more accurately and provided a better picture of to what depth the parking lots were inundated and how long the it took to drain the excess water. Therefore, this approach aided in prioritizing remediation work required to make the site drainage satisfactory. The performance of the existing drainage system of the site is presented under different design storms with varying return periods.