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Scattergraph Principles and Practice

PART 7 - Self-Cleansing in Existing Sewers

June 30, 2020 @ 12 Noon EDT, 11 AM CDT, 10 AM MDT, 9AM PDT

The scattergraph is a powerful tool that displays depth and velocity data from a sewer flow monitor, and the resulting patterns form characteristic signatures that provide insight into conditions within a sewer. The Scattergraph Principles and Practice webinar series is designed as an educational resource for wastewater professionals to understand how to use scattergraphs to recognize various flow conditions and understand how they impact sewer capacity and performance. This topic will be covered in a multi-part series.

Presentation Duration: Estimated 1 hour

PART 7 - Self-Cleansing in Existing Sewers
June 30th at 11 am CDT

The purpose of Part 7 is to discuss how to evaluate self-cleansing conditions in sewers. The Tractive Force Method is used to design sewers with self-cleansing conditions based on a critical shear stress, and this approach can also be extended to the evaluation of existing sewers under actual conditions. Self-cleansing conditions are assessed by evaluating flow monitor data on a scattergraph using a critical shear stress curve. Existing sewers with adequate self-cleansing conditions are readily identified, as well as those with a potential for silt, sediment, or debris accumulation. Practical examples from flow monitor locations throughout the United States are provided, demonstrating the application of the Tractive ForceMethod to existing sewers.

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PART 1 - Fundamentals
Duration: 50 minutes

The purpose of Part 1 is to provide a basic understanding of scattergraphs, including the fundamentals on which they are built. An overview of uniform flow conditions is provided, as well as the Manning Equation that represents them. Insights that can be gained by viewing flow monitor data through the lens of the Manning Equation will also be discussed. Important things can be learned by noting when they agree and when they disagree. These fundamentals provide a basic understanding of scattergraphs and serve as building blocks to more advanced principles to follow in this webinar series.

PART 2 - Backwater and Surcharge Conditions
Duration: 47 minutes

The purpose of Part 2 is to discuss backwater and surcharge conditions in sewers, including how to recognize them in scattergraphs of flow monitor data. Iso-Quantity or iso-Q™ lines will be introduced and used to demonstrate the effects backwater and surcharge conditions have on sewer capacity and sewer performance.

PART 3 - SSOs and CSOs
Duration: 54 minutes

Sewer overflows pose a significant threat to public health and the environment, contributing to beach closures, contamination of drinking water, and other concerns. Knowing when and where they occur – as well as their duration, volume, and frequency – are important pieces of information needed to assess their impact and minimize their future occurrence. The purpose of Part 3 is to discuss sanitary sewer overflows (SSOs) and combined sewer overflows (CSOs), including how to recognize them in scattergraphs of flow monitor data. Practical examples from flow monitor locations throughout the United States are provided, demonstrating the scattergraph signatures of SSOs and combined sewer overflows CSOs under various conditions. Techniques are also developed to estimate their duration and volume from flow monitor data.

PART 4 - Pump Stations, Siphons, Valves, and Other Structures
Duration: 48 minutes

The purpose of Part 4 is to discuss how to evaluate the performance of pump stations, siphons, valves, and related structures under certain conditions. A flow monitor located upstream from such structures can provide important information about their operating characteristics. This information is revealed any time a flow monitor operates within backwater conditions influenced by them. The addition of iso-Q™ lines to a scattergraph allows their actual performance to be compared to anticipated performance. Practical examples from flow monitor locations throughout the United States are provided, demonstrating the scattergraph signatures of approach conditions to them.

PART 5 - Subcritical and Supercritical Flow
Duration: 54 minutes

The purpose of Part 5 is to discuss the practical application of the Froude Number to flow monitoring. Engineers are aware of the instability associated with critical flow conditions and are generally advised to avoid them during sewer design. However, such conditions are often encountered in existing sewers and can impact the reliability of flow monitor data.
The Froude number (Fr) is a dimensionless number used to describe flow conditions within a sewer. These conditions can be illustrated on a scattergraph using iso-Froude lines. Certain flow conditions such as hydraulic jumps, sewer bores, and undular jumps are readily identified by evaluating flow monitor data with respect to iso-Froude lines. Practical examples from flow monitor locations are provided, demonstrating the scattergraph signatures of various transcritical and near-critical phenomena. Flow monitors can operate well in sewers under subcritical and supercritical condition, but accuracy may deteriorate near the transition. Such conditions should be avoided when possible in flow monitoring applications.

PART 6 - Flow Monitor Performance
Duration: 54 minutes

The purpose of Part 6 is to discuss how to evaluate the performance of a flow monitor. Previous webinars in this series have discussed characteristic scattergraph patterns that reveal insight into sewer performance and capacity. However, the flow monitor data also leave distinct patterns that allow the performance of the flow monitor itself to be evaluated as well. Practical examples from flow monitor locations are provided, demonstrating the scattergraph signatures of flow monitors that are operating as expected and some that are not. Best management practices to obtain high quality data will be discussed, as well as what to do when data quality is less than expected.

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Webinar Archive

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