Pipe Selection for Transient Control and Energy Savings

The Chattahoochee Raw Water Transmission Mains for DeKalb County provide the entire water supply for over 750,000 residents in the Atlanta, Georgia area. The pipelines are along a 13,000 foot easement from the pumping station on the Chattahoochee River to the new Scott Candler Water Filtration Plant on Winters Chapel Road. The existing pipelines were installed in three phases, in 1942, 1960 and 1980. A new 72-inch diameter pipeline was planned to replace the two older mains, to alleviate the issues of pipe transient damage, reliability and capacity. Detailed transient analyses of the existing pipe network (30", 48" and 60") confirmed the location of significant surge pressures, both positive and negative, and correlated with the evidence of breaks in the field. A pipeline was required that would reduce this surge potential, for both current flows of 140 mgd and for the ultimate pumping capacity of 300 mgd. An analysis of pipeline sizing to reduce transients, and to optimize pumping head, led to increasing the new pipe from 72-inches to 96-inch diameter. Through proper sizing of the transmission main, operating costs will be reduced to their optimum level, and the savings will offset the incremental cost of the larger pipeline. This paper provides a summary of the analyses, and how this approach can be applied for optimizing pipe selection for major transmission mains.