Depth Measurement


Depth Measurement is Key to Usefulness of Flow Data

As published in WATERWORLD Magazine, September 2005

Applications: 

  • Long-Term Monitoring
  • Flow Measurement Technologies 
  • SSO Monitoring

By Patrick L. Stevens, P.E.

Sorting through the nearly identical performance claims by manufacturers of open channel flow monitors is both challenging and puzzling. A buyer today who conducts a quick review of accuracy specifications for flow monitors will find that the self-stated accuracies are almost the same for all manufacturers.

Conventional wisdom suggests that meter sensor technology and monitor accuracy should be the key features that drive a purchase decision. However, marketing campaigns for flow monitors are based on other features intended to appeal to buyers, such as access to data over the Internet, satellite data collection, or direct measurement of average velocity. In these marketing strategies the measuring technology itself has become a secondary issue and many buyers don’t know the nuts and bolts of flow monitoring technology. Flow monitors should be selected first by the depth technology, second by the velocity technology and third by a combination of software, battery life, reliability and other issues that relate to your specific application.

The EPA has responded to the difficulty faced by sewer agencies as they try to sort through the performance claims by manufacturers of environmental equipment. Several years ago EPA developed the Environmental Technology Verification Program to verify performance of several types of air and water related equipment including flow meters. See http://www.epa.gov/etv/verifications/verification-index.html.  

To date, few monitor manufacturers in the flow measurement business have submitted their monitors for testing. Until the manufacturers all agree to submit their equipment to a common method of verification, such as the EPA’s ETV Program, most consumers will have to depend on their own experience or the experience of their peers to distinguish between the different technologies.

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