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This report offers a cost effective detection method to locate flow restrictions in gravity collection systems. The information needed to assess the collection system includes a representative map showing pipe size, flow direction, location of manholes, and the number of flow sources between manholes. This data combined with measurements collected in the field is utilized for the evaluation of the hydraulic capacity of the system. The same information, organized by the flow hierarchy of the collection system, then become ingredients to build into a database that provides an evaluation methodology to prioritize maintenance efforts or areas of concern. This evaluation technique is called “QFlow", or quantitative flow analysis.

The QFlow methodology is quite simple. As collection system maps are authenticated, an estimate is made of flow sources between each manhole. This is described as determining “anticipated” flow. To be more specific, based on the number of upstream sources with their associated flow rate(s), the conveyance pipe size and conventional construction design parameters, anticipated flow depth is computed. The anticipated depth of flow as associated with each manhole is then listed in a database. Following the computational work in a systematic manner, field personnel simply measure the depth of flow at a given manhole. This measurement is used to estimate the actual, or “theoretical", flow present in the pipe. Comparing the anticipated flow depth with the measured depth offers relevant information about the presence of a downstream restriction or blockage. The flow data and piping geometry are also used in the analysis of the available conveyance capacity of pipe segments, offering additional information to prioritize future planning of maintenance and capital improvements. With disciplined data collection, the utility can monitor changes in flow geometry during wet weather for low cost assessment of areas that contribute to sanitary sewer overflows or service problems.

QFlow is appropriate when considering a number of factors:

The equipment and information used for evaluation are readily available at a low cost.

Specific to field activity, inspections are quick and require minimal training. No confined space entry is required.

Similar to conventional methods of flow metering, the evaluation is primarily conducted at manholes.

The field inspections are done year round and are not wet weather dependent.

Analysis of the collection piping enhances planned maintenance and reduces the need for reactive maintenance activity.

Document Type: Research Article


Publication date: January 1, 2005

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  • Proceedings of the Water Environment Federation is an archive of papers published in the proceedings of the annual Water Environment Federation® Technical Exhibition and Conference (WEFTEC® ) and specialty conferences held since the year 2000. These proceedings are not peer reviewed.

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