This data is the result of a drainage analysis developed in 2023. The analysis was based on the City’s stormwater infrastructure data and a Digital Elevation Model (DEM) derived from Light Detection and Ranging (LiDAR) captured in March 2022. City outfalls that discharge stormwater to surface waterbodies either directly or indirectly were identified as points for analysis. UIC infrastructure was also analyzed to distinguish between infiltration-only basins and basins draining to the Municipal Separate Storm Sewer System (MS4). Five rules were developed to account for Underground Injection Control (UIC) drainage and refine the MS4 basin areas.

1. Overland flow paths not modeled to drain to the river were excluded.

2. Modeled basin boundaries were adjusted to align with streets.

3. Subbasins connected to isolated UICs were included (i.e., 2-3 UICs spatially isolated from other groupings, or networks of UIC systems).

4. Topographic breaks were followed when adjacent streets were not available.

5. UICs that met uncertain performance thresholds as noted in the UIC Aging Evaluation (Infiltration Study 2020) were included in the basin areas. UICs were excluded that were not located in watersheds associated with outfalls draining to the river, or where overland flow paths were modeled to drain to a network of dispersed UICs.