GIS

Cleaned-Up Approach to Sewer System Mapping

13 Nov, 2006 By: Kenneth Wong

Orange County Sanitation District deploys Autodesk Map 3D to ease CAD-GIS integration


Here's another side of Orange County -- the underbelly of the idyllic harbor-front community featured in the television show O.C. Beneath those pricey mansions and their perfectly manicured lawns run 581 miles of sewer lines. Every day the complex network of pipes and tunnels directs 233 million gallons of wastewater -- the output of 2.5 million people -- into two treatment plants. Then it pumps the treated content into the ocean 200' below the surface.

It's up to the Engineering Data Management Group at OCSD (Orange County Sanitation District) to keep track of all the manholes, pump stations, pipes, valves and other structural elements within this wastewater collection system so the field crews know exactly where each asset is. This aspect of Orange County life isn't glamorous or fun, but somebody's got to do it. And it does get a bit easier with Autodesk Map 3D.


A view of one of the water treatment plants of the Orange County Sanitation District.

Down the Manhole

About four years ago, OCSD began the Trunk Sewer Mapping Project, an ambitious undertaking to consolidate all the record drawings of the assets to construct a comprehensive map of the wastewater collection system. The dataset would eventually become part of the online sewer atlas.

"A lot of attributes tied to these assets -- the size of a manhole, the diameter of a pipe, the rim elevation and so on," says Doug Rulison, an OCSD engineering data management specialist. "The Engineering Data Management Group is responsible for providing and maintaining the online sewer atlas, which is a GIS database. We're also responsible for providing hardcopy map books for the field crews."


The OCSD's online sewer atlas, the outcome of a previously compiled AutoCAD database with new GIS tools.

Because of limited resources and unfamiliarity with enterprise GIS systems at the time, OCSD's engineering and IT departments agreed on AutoCAD as the archival file format for the Trunk Sewer Mapping Project. The outcome was a map book compiled from DWF file prints.

During those four years, while the AutoCAD map book was slowly coming together, OCSD hired several GIS specialists. "They started developing shape files, different layers, and the GIS work began to grow," recalls Rulison, "and management began to see that this was something they could benefit from."

By the time the AutoCAD map book was completed, management was entertaining ideas about building a GIS database. This presented Rulison and his colleagues in the Engineering Data Management Group with a dilemma: How do you make good use of the existing AutoCAD drawings in the new GIS environment? The answer was Autodesk Map 3D.

Divided by Technologies, United by a Tool

"Ultimately, we want all this data to reside in one database, one file format, but now we maintain two -- the AutoCAD version and the GIS version," says Rulison. Because the dual-dataset environment will likely remain for the foreseeable future, the OCSD needs a tool that accommodates data entry tasks by both CAD and GIS technicians. To that end, OCSD is investigating Autodesk Map 3D's FDO (Feature Data Object) tool for possible deployment.

"Autodesk Map 3D's FDO will allow us to pick and choose who our data entry people are," says Rulison. "With FDO, AutoCAD users can capture their data using an AutoCAD interface; the GIS users can do the same from a GIS interface."

The OCSD currently uses a combination of technologies from Autodesk and ESRI in its workflows. "Many organizations have wasted an incredible amount of time maintaining redundant CAD and GIS datasets," says Rulison. "We did not want to do that. The math is simple: It takes longer to capture the same data twice in both CAD and GIS. And let's face it -- redundant and manual processes tend to be more error-prone."

New Species in the Sewers

To those who are considering a similar CAD-GIS consolidation project, Rulison advises: "Understand the purpose of the data you're dealing with. A lot of the time, a CAD or GIS technician doesn't take the time to understand the function of the data." This understanding will be critical in determining how to best map certain CAD components to the GIS database.

One example from OCSD experience helps illustrate Rulison's point. OCSD's GIS database is connected to its CMMS (Computerized Maintenance Management System), which houses a database of all manholes and sewer lines. CMMS relies on GIS for asset updates to the system. For the database, the unique sewer IDs are derived using the IDs of the upstream and downstream manholes -- in other words, the combination of two manhole IDs makes up the sewer ID. During the quality-assurance process, OCSD discovered an undocumented manhole type.

"It was something called 'the cleanout,'" Rulison recalls. "We've identified five manhole types, but the 'cleanout' wasn't among them. It's structurally different from a manhole but functions as one in our system." As it turns out, the cleanouts are access points where maintenance crews can flush water into the system. But the CMMS group's business processes never demanded a record of the upstream manholes for the cleanouts, so generating a sewer ID using the established naming scheme was impossible.

How do you then assign maintenance work on a cleanout, or an asset not referenced as part of a sewer? Based on analysis of the cleanout's function and a clear understanding of how the data would be used, Rulison's group decided to classify it as a subclass of manholes.


About the Author: Kenneth Wong


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