WATER + STORMWATER
are deeper than the lowest intakes that send water to New York City, which makes them inaccessible for water supply purposes. That’s why the reduction in storage, at this point, has no negative effect on the quan- tity or quality of drinking water that passes through the water supply. The new data also did not affect the water supply system’s safe yield — a measurement of the maximum amount of drinking water that the system could provide under the most severe drought. In addition, the findings of the USGS study do not significantly affect cold-water vol- umes that are available for downstream releases. Based on the data collected by USGS, DEP has determined that no action is needed at this time because the reduction in storage capac- ity is relatively small and it does not affect water supply operations. The findings do not justify the cost and risk of dredging within the reservoirs, especially because such work would yield no water-supply benefits. However, DEP might look toward building expertise within its science and engineering staff to conduct similar studies more fre- quently in the future. This would allow the city to collect more data and better understand the rate of sediment deposition over time.
Tracking reservoir storage is one of many scientific efforts that DEP has undertaken to gather data for long-term planning, a principle that has guided the New York City water supply since it was established in the 1800s. DEP collects and regularly examines similar data on the ef- fects of climate change, numerous water quality parameters, and more. The new USGS data are also complemented by studies through DEP’s Stream Management Program. Working with its county partners, the StreamManagement Program is currently studying the rate of sediment transport and deposition for storm events of different intensities. Data show that recent stream projects — which aim to reduce the transport of sediments by correcting bank failures, reconnecting streams to their natural floodplains, and more — have reduced the amount of sediment moved by streams in the Catskills Mountains during typical storms. Download a copy of the final USGS report at www.nyc.gov/html/dep/ pdf/reports/catskill-delaware-bathymetry-study.pdf.
Information provided by the New York City Department of Environmental Protection (http://nyc.gov/dep).
Utilities that provided data serve a population of more than 52 mil- lion people, representing 14.5 percent of the total population of the U.S. and Canada. The survey recorded 23,803 pipe failures that needed repairs, which is a significant basis for break data. This is one of the largest surveys conducted on water main breaks and the results give an accurate representation of water pipe condition and operation in North America, according to USU. The report can assist in revising pipe ser- vice life assumptions used in the past. Water main break rates are an important calculation to assess pipe per- formance and durability, and are the most critical metric used in water infrastructure asset management as well as pipe repair and replacement decision-making. “This report provides greater insight into the drivers of the aging water infrastructure crisis and offers data which utilities can use to bench- mark pipe material performance. It will be a valuable asset manage- ment planning tool for water utilities,” Folkman said. Overall, break rates have increased 27 percent in the last six years. Utilities should be concerned that break rates for cast iron (CI) and asbestos cement (AC) pipes, which together represent almost half of the installed water mains in North America, have increased 46 percent and 43 percent, respectively, since 2012. Together, CI and AC pipes are mostly responsible for the spike in pipe failures. CI and AC pipes are no longer manufactured and are now reaching the end of their expected lives.
Water main break rates rise
Survey of North American utilities indicates break rates have increased 27 percent since 2012.
Utah State University’s (USU) Buried Structures Laboratory published a second comprehensive study on break rates of the most commonly used water pipe materials. The Buried Structures Laboratory has a large-scale testing facility for pipes and underground structures. USU is also home to the Utah Water Research Laboratory (UWRL), which has been a world leader in environmental research and water policy for more than 50 years. UWRL is the oldest university-based water research facility in the U.S. Steven Folkman, Ph.D., P.E., co-author of Buried Pipe Design and au- thor of a 2012 USU water main break report, completed a new pipe ma- terials survey in which more than 300 utilities responded, representing approximately 200,000 miles of installed water mains. The 2018 study, Water Main Break Rates in the USA and Canada: A Comprehensive Study, obtained respondents from 48 states in the U.S. and seven out of 10 provinces in Canada, representing a 49 percent increase in survey responses and 45 percent more miles of pipe compared with the 2012 study, increasing its statistical validity.
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csengineermag.com
may 2018
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