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Project Profile

Dallas Uses GIS Technology for Storm Sewer Inventory

By Bryan Stockton

Responding to obligations outlined in the city’s National Pollutant Discharge Elimination System permit, the Dallas Public Works and Transportation Department’s Storm Water Quality Section has used geographic information system (GIS) technology to map the city’s storm sewer network. Using existing off-the-shelf software, a dedicated and talented staff developed and tested an inventory system in one year.

SDE_QC user screen (click here for a larger view)

Dallas has an extensive storm sewer network in its 378 mi.2 To comply with permit requirements, the city must complete an inventory of all conveyances, including belowground pipes and aboveground ditches and canals used to convey stormwater. The city is also videotaping the entire storm sewer network using closed-circuit television (CCTV) technology. The multiyear, multiperson inventory project gathers data about the location and attributes of the storm sewer network and stores this information in an Oracle database.

An initial review of GIS products on the market revealed that existing products would not meet the city’s needs. Database models from vendors did not prove flexible enough; many products did not allow the use of database triggers or constraints or the ability to work with optional program extensions.

GPS crew member inventorying storm sewer manhole

To support the creation, updating, and reporting of a database for the storm sewer inventory data, Dallas programmers incorporated several software packages into the inventory system: Trimble global positioning system (GPS) software for accuracy, Oracle’s RDBMS (Relational Database Management System) version 8i for stability, and ESRI’s ArcView GIS 3.2, which provides analysis and reporting capabilities. The system also uses ESRI’s Spatial Database Engine (SDE) version 3.

Oracle is used to hold and manipulate all nonspatial data in the database. SDE, which can be thought of as an extension to Oracle, provides management of the spatial information. Oracle also provides protection of the data by assigning user roles. The database design is performed using Sybase’s PowerDesigner 6.1.4. The design includes both conceptual and physical models.

The applications are built using ESRI’s ArcView and Sybase’s PowerBuilder version 7.0.2. The main ArcView application, SDE_QC, provides viewing, editing, and plotting capabilities for the storm sewer and discharge point inventory data. SDE_QC also provides a means for loading data into the Oracle/SDE database. The PowerBuilder application is SDE_Print, which provides reports of the inventory data.

Status map

City crews are carrying out the inventory, working in four two-person teams. Accuracies of ±1 m are currently sufficient for the inventory program, and this accuracy is consistent with existing digital orthophotos of the city.

Using the program, crews can view the current GIS data for storm sewer and discharge point inventory, edit GPS and attribute data for storm sewer nodes and lines, load GPS data into the inventory database, and view and control the status of maps. Database forms are also available for adding information on the portions of the storm sewer network that have been inventoried with CCTV. Updated inventory maps of the storm sewer network include data on size, flow direction, pipe material, and appurtenances.

Now 60% complete, the inventory should be entirely finished in three to four years. However, there will be an ongoing need to use GPS and CCTV to document new storm sewer construction. The city will investigate the possibility of requiring contractors to provide storm sewer maps of their new construction in a GIS format.

The city will also investigate migrating the system to ESRI’s Geo-Database model using ArcSDE and Arc 8. The change would make it easier to include other types of field-collected data in the database, such as video clips of inspected pipe sections and older CAD drawings of the storm sewer network.

Bryan Stockton works for the Dallas Public Works and Transportation Department. He has spent 15 years working with all phases of GIS, including database design and development.

 

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