Description of Study Area

The study area, having an area of 48.8 acres, is primarily an undeveloped land that has a coarse loamy soil, and depressions located at vegetative areas. All the streets are, in general, followed the natural slope, and the adjacent areas to Queen and Lopez Streets are located at a lower elevation comparatively. However, in post-development scenario, the residential lots will be graded toward the street at a slope of 2% so they can drain easily. Currently, the entire catchment drains to the outfall located at the confluence of Queen Street and Edwards Street to the north of the study area.

Surface imperviousness has significantly increased and continues to increase as development takes place. This has exacerbated the runoff volume and peak overland flows during rainfall events, eventually increasing the receiving flow at the site outfall. In this tutorial, the impact of this change has been analyzed by constructing two storm drainage models in GeoSWMM. The first one is prepared with the drainage properties of undeveloped scenario (prior to urban development), and the second one represents post- development urban catchment.

The following Figure 2.1 and Figure 2.2 show the layout of the catchment area in undeveloped and post- developed conditions respectively. The developed site is divided into 16 subcatchment utilizing the Watershed Delineation Tool of GeoSWMM. For both conditions, the site drains to the same outfall O1. Table 2.2 lists the model object quantity summary for both scenarios.

Table 2.2 : Network Object Summary