HESCO ProactiView - A Look at Water and Wastewater Issues You can Use

Taking a "proactive view" on fundamental and emerging water and wastewater issues has enabled HESCO to provide the most effective and affordable process and technology solutions to our clients.

A staggering amount of information is available on innovative technologies and processes for water and wastewater treatment. Unfortunately, few people have the time, patience or expertise to sort the critically important from the unnecessary noise.

Therefore, HESCO sees the value and opportunity to share its technical knowledge, expertise and process experience with the water and wastewater professional community through the monthly ProactiView of distinct industry issues and concerns.

HESCO ProactiView on: Flow Metering

Engineers and Collection System personnel have long struggled with accurate and effective means to measure flows in their sewer systems.  These issues are now critical as regulations tighten, populations increase, and our infrastructure ages, placing greater stresses on urban and rural collection systems alike.  Meanwhile, the public is more aware of these issues than before, and the need to collect more accurate and reliable data is more important than ever.

This issue of the HESCO ProactiView serves to detail the major issues in collection system monitoring and highlight some tools which may be helpful in monitoring these systems. See below for instructions on how to request your FREE copy of the newly released Sixth Edition of the "Isco Open Channel Flow Measurement Handbook".

Contents

Needs for Flow Metering
Measurement Devices and Approaches
Matching Metering Technology to the Application
Data Management and Analysis
Follow Up With HESCO Regarding Flow Metering

Needs for Flow Metering

There are many reasons why a professional may want to implement a flow metering program within their community:

• The POTW may be over capacity.  Specific strategies can be employed to target and eliminate sources of Inflow and Infiltration (I&I), thereby reducing the flow to the plant, possibly staving off or postponing the need for a costly plant expansion.
• Certain areas of the collection system may be overloaded and prone to overflow.  Effective flow metering programs can identify underutilized areas of the collection system that can be utilized for storage, or determine the required capacity for a CSO or SSO basin.
• Growth in a community may require increasing the capacity of the existing infrastructure.  Implementation of a flow metering program will allow professionals to determine the appropriate size and location of new trunk lines and interceptor sewers to handle the growth.
• Communities may share infrastructure and need an effective and accurate method to quantify the flow in order to share in the costs of operating and maintaining the system.  Employing the proper flow metering techniques will ensure the most accurate and reliable measurements in a custody transfer or billing application.
• Effective maintenance and operation. Collection managers can maintain and operate their systems more effectively when the flows are metered in strategic locations and the data from those areas are comprehensively stored and reported. The system can then notify appropriate personnel when specific anomalies occur.

Measurement Devices and Approaches

Once the reasons for implementing a flow monitoring program are understood, there are many options available to measure the flow.  Each option has its own strengths and weaknesses.  The following is a description of some of the most commonly implemented technologies:

• Magnetic Meter:  a device employing "Faraday's law" in which a magnetic field is induced across a flowing conduit.  The velocity of the water induces a voltage proportional to the velocity that is measured by the meter.  The inferred velocity is multiplied by the cross sectional area of the meter tube to calculate flow.  In certain situations, this method can be a highly accurate means of measuring the flow, however, the conditions that regularly occur in a sewage system make measuring the average velocity of the system difficult.
• Continuous Wave Doppler:  a device that employs an acoustic probe and level sensing device in a single sensor.  This device emits a sound wave into the flowing material and senses the Doppler shift caused by the velocity of the particles present in the flowing water.  From this shift in frequency an average velocity is calculated and utilized to compute the flow rate by multiplying the area of the flowing water by the velocity of the water.  This method of measuring flow has been implemented successfully many times in a variety of applications and is widely recognized as a very versatile method of flow measurement.
• Range Gated Doppler:  a device that is an improvement over the continuous wave Doppler technique in that it incorporates multiple acoustic sensors in a single probe to determine the actual velocity profile present in the pipe.  From this velocity profile, the average velocity is much more accurately calculated, resulting in a highly accurate flow rate calculation.  This technology is beneficial in chain of custody applications or applications where highly accurate flow measurement is desirable.
• Flume:  a specially engineered hydraulic structure that forces the flowing water to behave in a specific manner at varying flow rates.  The height of the water level at a specific point within the flume can be measured to determine the flow.  A properly designed flume system has the major advantage of accelerating the flow through the flume, thereby leaving it less prone to problems due to sedimentation and/or blockages.  Furthermore, flumes are well understood hydraulic structures and their accuracies are widely accepted by governmental bodies.
• Weir:  an obstruction built into a channel that increases the height of fluid above the weir crest by an amount relative to the amount of flow.  The liquid height is measured to determine the flow.  Depending upon the application, there are a variety of well understood weir shapes that can be implemented.  One major disadvantage of a weir is that it physically obstructs the flow which increases head upstream of the weir and may cause problems with sedimentation in front of the weir as well.  A major advantage of a weir is its simplicity. 

Each of the technologies described above are well understood and widely accepted means of measuring flow in collection systems.  This does not mean that each technology can be utilized in every application. 

Matching Metering Technology to the Application

In order to select the appropriate measurement approach, the individual technology must be matched to the application. this is largely controlled by the conditions present at the site and the data objectives required by the application.  The following table gives a starting point for understanding where each approach is well-suited for several general applications:

Approach by Application	Magnetic Meter	Continuous Wave Doppler	Range Gated Doppler	Flume	Weir
Small Diameter Conduit		X		X
Large Diameter Conduit	X		X	X
Inflow and Infiltration Study		X	X	X
Combined Sewer Overflow			X	X	X
Custody Transfer or Billing Site	X		X	X

For an expanded analysis of the various flow metering approaches for each application, consult the “Isco Open Channel Flow Measurement Handbook”.  This publication contains comprehensive information regarding the implementation of open channel flow measuring devices including flume and weir tables.

*See below for how to get a FREE copy of the newly released Sixth Edition, complements of HESCO!

Data Management and Analysis

Regardless of the method of measurement, the data collected from the device must be effectively collected, stored, organized and managed.  Without such a system even the most accurate flow meter will be of little value if the data is not readily accessible and quickly reported in formats that are appropriate for and meaningful to the specific user, and pertinent to the goals and objectives of the metering project.

If not properly planned for and organized, the data management and analysis portion of a flow monitoring program can become more labor intensive than planned for, exceed the budget, and potentially undermine the end product quality of the monitoring program.

An effective data management system should allow users to easily organize and access their data.  It will also produce reports such as tables, charts, and/or graphs that can be easily and quickly analyzed, so that effective collection system management decisions are based on real data instead of assumptions.  Some managers have developed sophisticated spreadsheets to perform these tasks, but these spreadsheets often become large, complicated and labor intensive to create and maintain. Traditional spreadsheet software programs also tend to become slow and prone to crashing with such large data sets.  Data analysis software is available that organizes data in a database structure, allows for the creation of standard and custom reports at the push of a button, and facilitates more complicated data analysis operations more commonly referred to as “meter math”.

Follow Up With HESCO Regarding Flow Metering

The world of flow metering is a vast and complicated field.  Some even say that it is more of an art rather than a science.   HESCO has the experience necessary to help collection systems professionals successfully tackle any problem they may face. 

You may request a COMPLIMENTARY copy (while supplies last - a $50 value) of the “Isco Open Channel Flow Measurement Handbook” when contacting us.  Be sure to supply your mailing address and answer ALL of the questions below.

There are three immediate ways that you can contact us:

1.  Call Kevin Livingston or Glenn Hummel at 586-978-7200 and mention that you are following up on the ProactiView on Flow Metering.

2. Email Kevin Livingston or Glenn Hummel directly.  Be sure to include your name, contact information, and brief answers to the questions below.

3.  Answer the questions below and click the Submit button.  This will generate a web-based response that will go directly into our contact management system.