The current drainage plan concentrates on volume of storage and conveyance capacity in the City's four watersheds (Atlantic Ocean, Elizabeth River, Lynnhaven River and Southern Rivers), which are made up of 15 drainage basins. 

The updated study will model the primary stormwater management system (PSMS). The PSMS is defined as pipes of 24” diameter or greater, equivalent open conveyance and associated outfalls. PCSWMM, a value-enhanced version of public domain EPA's  stormwater management model (SWMM), is being used for the update. This update will include a more robust network of secondary storm drainages systems and will include an analysis of BMPs and pollutant loadings.

As a portion of the update process, staff has populated the City’s GIS inventory to more completely represent the system. An analysis has been performed to identify missing data shown on the current GIS inventory; data such as pipe size, material, and invert elevation. This missing data is being delivered in several ways: using as-built plans, using original approved plans (often with field notes), and performing ground surveys when no record data exists. 

The source of the information including the date of the documents, any notation of applicable reference datum, and type of document, is included in the information added to the GIS inventory. All data is being converted to the North American Vertical Datum (NAVD) 88 for input into the models.​