BCWWA – The 14 Types of Sewer Hydraulics

Patrick Stevens from ADS Environmental Services presents on Scattergraphs Identifying Hydraulic “evil-doers” that Rob Sewer Capacity. (“Evil Doers” is in honor of G.W. Bush of course).

Patrick is the champion for using the North American Robin as the symbol of Sewer Service Providers in North America – the main reason being it’s latin name – Turdus Migratorius.

Patrick has spent years looking at the real capacity of sewers…
Three types of Sewer Capacity:

  • As-Designed
  • As-Built
  • Operational Capacity (accounts for operational hydraulic losses)

Traditional information from hydrographs derived from Flow Meters
A scattergraph is a display of paired depth and velocity readings – the pattern should look like a pipe curve – if it doesn’t either there’s a problem in the pipe, (not normal open channel flow), or the meter is not working.

Patrick discusses the accuracy of meters relating to a theoretical line of depth vs flow – the combination of Mannings Curve, meter data and confirmation (manual measurement) reveal that a meter is accurate.

Silt and Obstacles result in backwater readings in meters – Dead Dog effect.
If there’s obstacles downstream – a bottleneck occurs and HGL flattens, rather than following grade of pipe.
Negative Grade Pipe – Dead Dog and Orifice Flow (under head pressure).
Shifting Debris can change the pattern of depth.
SSO Upstream of meter – whole bunch of data at given height.
SSO and Bottleneck Downstream of Flowmeter

Conclusion – Scattergraphs can determine what’s happening in your sewermain – or what’s wrong with our flow meter.

Published by Mike Thomas

Mike Thomas P.Eng. ENV SP, is the author of UrbanWorkbench.com and Director of Engineering at the City of Revelstoke in the Interior of British Columbia, Canada.

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