CCTV cameras have been used for more than 40 years as a tool for inspecting small diameter sewer pipes. From black and white cameras with low resolution to today’s cameras with the capability of generating high-resolution digital color videos, significant improvements have been made in the technologies to capture, store and assess video images. The migration to digital format of both the inspection images and the defect logs has made the analysis of CCTV easier and more efficient. The progress in the development of analytical tools to assist with the analysis and interpretation of CCTV data has been remarkable.
Application of CCTV Inspection
The CCTV inspection of sewer lines may be performed for a number of reasons including:
- Preventive maintenance
- I/I source identification
- Structural condition assessment
- Pre-rehab survey of sewer lines
- Quality control (acceptance) of rehabilitation pipe work
- Quality control of cleaning and other maintenance
activities
- Complying with requirements of GASB34 modified (preservation)
approach
- Collecting asset condition data for asset management plans
- Troubleshooting investigations for backups and overflows
A survey performed for a research study for the American Society of Civil Engineers (ASCE) indicated wastewater utilities, on average, use CCTV to inspect approximately 7 percent of their system every year. Deciding which portions of the system to inspect is a challenge.
Several factors should be considered in crafting CCTV inspection programs. Some wastewater agencies focus their limited resources on older and more problematic parts of their system. The new trend in developing inspection programs is moving toward the concept of criticality and risk. In this approach, the utility makes an assessment of risk associated with each sewer line and prioritizes its system based on the level of risk or criticality. The results of such an assessment are then used to develop an inspection program to manage the risk and keep it below an acceptable level.
Data Storage & Manipulation
For many years, CCTV images were stored on reel or cassette. A shortcoming of such media was the gradual degradation of the video quality over time. Additionally, the size of the physical space required for storing the video tapes was an issue for larger utilities with a large volume of CCTV data. With the advent of digital storage, the use of video tapes has now become almost obsolete. The digital data is stored on DVDs or large capacity hard drives. This not only reduces the physical storage requirements, but also significantly enhances the process of accessing the data. Many utilities have started building and developing asset management software with GIS interface capabilities that allow easy and efficient access to the CCTV data. In a typical application, a sewer segment of interest is selected in the GIS environment and with a few clicks of the mouse button, a graphical presentation of CCTV observations is generated, see Figure 1. The data for each observation, including video clips and still photo images, can be viewed by simply selecting the observation of interest in the graphical presentation of observations.
This article first appeared in the May/June 2008 edition of Underground Infrastructure Management. The author, Ahmad Habibian, Ph.D., P.E. is a national practice leader-pipeline rehabilitation at Black & Veatch Corporation. He can be reached at habibiana@bv.com.
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