Measure 3c:  Develop a storm sewer base map

“Complete identification, locations of and mapping of stormwater drainage system components. At a minimum, mapping components include outfalls, drainage areas and receiving streams.”

The purpose of the storm sewer system map is to give the Phase II communities a basic awareness of their storm sewer systems.  Once the map is established, it can help Phase II communities determine the possible sources of dry weather flows and identify which waterbodies these flows may be affecting.  The storm sewer base map could be an existing map, such as a topographical map, which clearly shows the locations of major pipes and outfalls.

As you begin working on your storm sewer base map, you should audit the coverage and quality of mapping resources available to support the IDDE program.  You should see if a Geographic Information System (GIS) exists and what digital mapping layers it contains. 

If your community does not have a GIS, you have three options:

  • Establish one (which can be quite expensive),
  • See if a nearby larger local government will share their GIS capabilities with you, or
  • Rely on available hardcopy maps.

GIS and hardcopy maps are frequently available from the following local agencies:

  • Planning
  • Tax assessment
  • Public works
  • Parks and recreation
  • Emergency response
  • Environmental
  • Transportation
  • Utilities
  • Health

Your initial storm sewer map should include all existing information on outfall locations as available from the agencies listed above.  Then as you conduct stormwater outfall inspections (see Measure 3d), you will field verify the locations of the outfalls and make corrections to your storm sewer map as needed.

For an example of a mapping project in a Phase I community, see the City of Greensboro’s Stormwater Infrastructure Inventory project. Greensboro is working on a big upgrade from its current hand-marked storm sewer maps.  The Stormwater Infrastructure Inventory will include: (1) determination of the location of each structure; (2) collection of structure attributes; and (3) development of a Geographical Information System (GIS) database that includes all of the information on the storm water conveyance system.