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The City of Dallas recently awarded a $1.3 million contract to Byrd/Forbes Associates, Inc., which will employ American Sigma 950 Portable Area Velocity Flow Meters to perform temporary and permanent flow monitoring. The overall project includes GPS (x, y, and z) of each manhole for use in updating system maps and construction of a dynamic hydraulic model. Manhole inspection, smoke testing and CCTV inspection will be undertaken within the study area.
The installation of the permanent flowmeters at key locations throughout the city is the latest phase in a multi-year project and is scheduled for completion later this year.
The history of the Dallas sewage collection system predates the turn of the century. In 1876, the first 24-inch sewer pipe was built in downtown Dallas, transporting wastewater to the river. What is now known as the wastewater collection system, however, began operating in the early 1900s.
The collection system has grown with the city and now serves a population of more than 1.1 million people through approximately 4,100 miles of sanitary sewer mains. These mains transport wastewater produced by city residents and businesses to Dallas' two wastewater treatment plants.
Dallas is now in the process of implementing a system to monitor the wastewater levels and flows. The project is part of the recommendations resulting from the Major Interceptor Study of the Wastewater Master Plan update. Once this system is in place, wastewater collection and wastewater treatment plants will receive real time flow information from as many as 70 sites throughout the city.
"We looked at three or four different systems and thought American Sigma's met all our requirements," said Morgan Rastegar, a senior engineer with the Water Utilities Department of the City of Dallas. "Our wastewater collection system is a major capital investment, and in order to ensure safe and efficient service to our customers, we want to get an accurate picture of what the sewer system is doing throughout the city."
"A capacity analysis had to be done to deal with the expansion and design changes in the system," said Gregory J. DeSantis, Director of Strategic Accounts for American Sigma. "In addition, we had to ensure that we could get event-notification information to the maintenance crews as soon as possible. We can do that by plugging into an existing radio network."
In fact, the Sigma 950 has a unique eight-line by 40-character display that makes it simple to check data instantly, right in the field, in graphic or tabular formats that does not require a laptop computer. The incorporation of MODBUS protocol for use in SCADA (Supervisory, Control and Data Acquisition) also allows the end user's PC to directly communicate with the 950 flow meter using an industry standard protocol.
The 950 AV's higher frequency one-megahertz Doppler with signal amplifiers also provides reliable velocity readings in low levels and clean water.
"What sold us on the American Sigma flowmeters was the velocity component," said James Forbes, Vice President of Engineering for Byrd/Forbes Associates in Dallas "The American Sigma flowmeters measure a true average velocity, as opposed to a peak or point velocity that has to be factored back to the average.
"The recording of average velocity reduces significantly the time required to install and calibrate the flowmeters," Forbes added. "The 950 also incorporates a patented drawdown feature that corrects for the effects of velocity on level measurement."
Approximately 15 of the flowmeters will be installed permanently in the Dallas sewer system during the first phase. The long-term meters will monitor the system, look at the trends as they develop and evaluate how the system is performing hydraulically. In addition, the permanent flowmeters will be employed to keep the dynamic hydraulic model calibrated for wet and dry weather flows.
Zachary Peoples, Manager of the City of Dallas' Wastewater Collection Division, believes that flow monitoring devices such as American Sigma's and sewer evaluations and flow analyses like the ones conducted by Byrd/Forbes Associates are vital to the proper operation of aging sewer systems.
"As our sewers deteriorate with age, we are dedicated to ensuring that we are allocating the proper amount of money each year on maintenance," Peoples said. "This will help us to avoid unexpected large sewer maintenance expenditures at one time."