Automated Sewer Video Assessment Tools Expedite Decision Process

The San Diego Metropolitan Wastewater District faced a daunting task: First, videotape the worst 1,000 miles of its 3,000-mile wastewater collection system...

Oct 1st, 2003

The San Diego Metropolitan Wastewater District faced a daunting task: First, videotape the worst 1,000 miles of its 3,000-mile wastewater collection system over a relatively tight timeframe —within four weeks. Then, categorize each line segment into one of four categories: maintain, repair, rehabilitate or replace for dispatch to design groups. With an average of 20 line segments per mile, this equates to assessment and categorization of approximately 20,000 line segments.

To obtain consistent and objective classification results from the assessment team, HDR developed a decision flow diagram as a guideline for the assessment process. Based on the type of defects present and the sum of the total defect points in a pipeline, the decision flow diagram helps assessors produce objective and consistent results.

In the process of developing this training tool, the design team realized that the yes/no, inclusion/exclusion nature of the decision-making process made it ideal for a computer. HDR engineer Jeroen Olthof wrote an Avenue™ script in ESRI Arcview™ 3.2 that extracts sewer defect codes and scores from the video contractor's electronic defect code databases and automatically processes the defect codes according to the decision flow diagram.

This automated process, coupled with the use of digital video loaded on a server in lieu of VHS tapes, has increased the quantity of line segments a typical person can assess from 10 per day to more than 30 per day, freeing up personnel and reducing the cost of the assessment program.

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