Hydraulic Calculations for Water Meter and Lateral Sizing

Calculations for Lateral Sizing in City of Santa Rosa

The City of Santa Rosa has recently been requesting hydraulic calculations to be performed by a licensed civil engineer to confirm that the velocity in service laterals and water meters will not exceed 15 feet per second. This will cause less wear and tear on the service lateral and meter, and limit the water loss due to small breaks and leaks. These calculations conform with American Water Works Association (AWWA) M22 Manual standards, which are the national standards for water systems. These standards combine best practices within the industry and the standards of other professional societies such as the Uniform Plumbing code.

To conform with the AWWA M22 Manual standards BC Engineering Group uses an iterative approach. The initial assumed water meter size is based on the AWWA meter requirements. Next, the velocity is calculated, and the water meter may be resized from the initial assumed value. Once the selected water meter yields a velocity that is within the appropriate operating range, comparison with other design deliverables is required. BC Engineering Group then compares the calculated lateral and water meter sizes to the recommendations from the fire suppression consultant to ensure that it will not conflict with what is necessary for the fire suppression system.

In certain cases, the calculated velocity can exceed the mandated velocity while conforming with the AWWA meter sizing recommendations when the project is located within a high-pressure area of the municipal water system.

AWWA recommends that water meter sizes match the service lateral diameter to limit head loss (pressure loss). AWWA publishes a set of recommendations for meters based on maximum and minimum flowrates. Water meters are less effective at velocities outside these recommendations. This can cause increased maintenance demands and incorrect billing to customers.

To get more information on this topic, or to schedule hydraulic calculation work, please contact the professionals at BC Engineering Group at 707-542-4321 or online at www.bcengineeringgroup.com