City of Los Angeles Monitors Critical Flows with Flo-Dar

Below the bustling streets of the largest city in California and the second-largest urban area in the U.S. lie 6,500 miles of sewers ranging from eight inches to 12 feet in diameter.  The City of Los Angeles' wastewater system is the largest wastewater collection system in the U.S. and serves over four million people in Los Angeles and 27 nearby cities that contract them for their public works services.  The four wastewater treatment plants in the system can process over 550 million gallons of flow each day.

While most residents and visitors to LA are unaware of the complexity of this enormous task (due in part to the 'out of sight-out of mindä thinking), it is definitely on the minds of the people that are employed by the Wastewater Collection Systems Bureau of Sanitation, a division of the cityâs Department of Public Works (DPW).  The Bureau of Sanitation has a staff of over 2,600 employees, almost half of the entire DPW staff.  The Bureau also provides services for refuse/recyclables/yard trimming collection, sewer and storm drain maintenance and repair, and wastewater collection and treatment, just to name a few.

Beginning in 1990, LAâs wastewater collection system flow monitoring program was contracted to a company that manufactures and maintains flowmeters and provides flow reporting services, also known as a turn-key package.  Frequent site visits requiring confined space entry for maintenance due to fouled submerged sensors and increasing monthly fees for data reporting and proprietary software, resulted in the city making a decision to look at alternative methods for collecting and reporting basin flows.

Four flowmeter manufacturers, including Marsh-McBirney, provided equipment for evaluation.  Two of the four companies being evaluated offered turn-key equipment/service packages to the city.  By contrast Marsh-McBirney was interested in providing a new generation of flow monitoring equipment coupled with easy-to-use reporting software that would allow the cityâs Engineering group to analyze the flow data themselves.  Gary Whitney, Staff Supervisor for the Wastewater Collection Systems group, became aware of the Flo-Dar Flowmeter from  local Marsh-McBirney's sales representative, Hykin Systems Automation.  Encouraged by the idea of a non-contact sensor, Whitney felt this could be the solution the city had been seeking.  "Continuous flowmeter maintenance costs are what really should be evaluated when selecting a flowmeter," he stated.  Whitney continues, "Tens of thousands of dollars in maintenance costs can quickly accumulate making the initial cost of the meter itself inconsequential.  The use of proprietary software and associated monthly fees offered by flowmeter manufacturers providing turn-key services should also be closely examined," noting that these monthly fees also add up very quickly.

The Flo-Dar Open Channel Flowmeter provides a revolutionary approach to open channel flow monitoring by measuring from above the flow stream eliminating confined space entry concerns and maintenance caused by fouled submerged sensors.  Flo-Dar transmits a digital Doppler radar beam that interacts with the fluid surface and reflects back signals at a different frequency than that which was transmitted.  The return frequency is compared with the transmitted frequency and the resulting frequency shift provides an accurate measure of the velocity and the direction of the flow.  Depth is detected by an ultrasonic pulse echo sensor.  Flow is then calculated based on the Continuity Equation: Q = V x A, Where Q = Flow, V = Average Velocity and A = Area.

Based on the outstanding performance of the Flo-Dar flowmeter in the comparison study, a unanimous staff decision was made to purchase 75 Intrinsically Safe Flo-Dar Model 460 (portable-battery powered) flowmeters.  The intrinsically safe version of the Flo-Dar system includes:

an intrinsically safe Flo-Dar sensor approved for installation in hazardous environments

a "barrier box" that is placed in a non-hazardous location between the sensor and the main electronics

the Flo-Dar electronics unit that is also located in the non-hazardous location

Barry Berggren, Division Manager for the Wastewater Collection Systems group, stated that the Flo-Dar flowmeter was chosen based on recommendations by his staff.  According to Barry, the most notable feature of the meter is "the non-contact sensor that has eliminated maintenance we used to experience caused by fouled sensors in the flow stream."   Installation of the 75 Flo-Dar systems was completed in December 2001.

Gary Whitney explained that the 75 flowmeters were ordered for the cityâs 'near-timeä flow applications.  The near-time applications required portable, battery powered units that would be installed in selected basin locations. Staff members would visit the sites on a pre-determined basis to download collected flow data that would in turn be forwarded to the Engineering group.  Professional flow data analysis is now easily accomplished by the cityâs own engineering staff utilizing Marsh-McBirney's Flo-Ware software - a user-friendly data management and report generation package that is compatible with both desktop and portable computers utilizing Windows¨.

Solving the need for real-time flowmeters
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