Posts Tagged ‘Water Towers’March 7, 2011
Water towers are something most of us probably don’t think about until we see one on the horizon. To Des Moines Water Works (DMWW), water storage facilities are a vital part of the infrastructure and a significant part of the utility’s history. DMWW owns and maintains numerous water storage facilities. From a technical standpoint, water storage facilities are divided into three categories: water towers, standpipes and ground storage. Water towers are basically large storage tanks on legs. Standpipes are simply tall vertical tanks. Ground storage reservoirs are shorter but larger diameter storage tanks that sit on or slightly below ground.
Des Moines’ first water storage facility was constructed in 1891 at 17th Street and Crocker. Made of steel with a lacy ironwork railing and spiral stairway, it held 530,000 gallons of water. It was torn down in 1939 after 40 years of service.
The Hazen Tower at 4800 Hickman is the oldest and technically, the only water tower in Des Moines. Constructed of concrete and steel in 1930-1931, the 110 foot tower, which holds 1.7 million gallons (mg) in its elevated tank, was named after Allen Hazen who designed the tower. A prominent New York engineer and pioneer in the area of water treatment, he died before construction was completed. For many years, a large arrow was painted on the top of the tower to point the way to the airport for pilots.
In 1955, two standpipes were built and named after long-term Board of Water Works Trustees members. The Nollen Standpipe at 26th and Hull is Des Moines’ largest, with a capacity of 4.2 mg. The Wilchinski Standpipe at SE 9th and Pleasantview Drive stores slightly more than 2 mg.
Probably the most familiar is the Tenny standpipe because of its location near Sears at Merle Hay Mall. Construction of this 4.1 mg water storage facility was completed in 1960 and named after Morris K. Tenny, who served as the General Manager of DMWW from 1955-1968.
Water storage facilities outside the city of Des Moines which are owned and operated by DMWW include two towers in Southeast Polk with a combined capacity of 0.7mg. The smaller tower (0.3 mg) located at 6538 NE 12th Ave., is scheduled to be removed the summer of 2011. Other facilities in Polk County include the Polk County Ground Storage Tank on NE 14th St. which holds 5 mg; the L.P. Moon Ground Storage Facility (named after a former Board member) in Clive stores 6 mg and the Shared East Side Elevated Storage Tank, which holds 2.5 mg, was built in 2009-2010, bordering between Pleasant Hill and Altoona. (Interestingly enough, Pleasant Hill’s logo is on the south side of the facility and Altoona’s is on the north side).
Water pressure is influenced by a number of factors including ground elevation, distance from the treatment plant or pumping station, piping materials, and even water demand on any given day. Ground elevation influences water pressure because pressure is actually created by lifting water into the air above the point of use. This is why water is pumped up into water towers – to raise it above the point of use thereby creating pressure. As a result of the influence that elevation has on water pressure, higher elevations in a service area experience the lowest pressures and lower elevations experience the highest pressures. Ground elevations in Des Moines range from 800 feet above sea level on the east side of the City near the Des Moines River to more than 970 feet above sea level in northwestern areas of the city. This 170 feet of elevation difference represents a water pressure variation of 75 pounds per square inch (psi). The distance from the pumping station and changes in water demand introduce additional pressure variation resulting in the potential for significant pressure differences across the city. Des Moines Water Works (DMWW) manages water pressure using pressure zones, water towers and booster pumping stations, like the new booster station near the Des Moines Airport.
The City of Des Moines is divided into four pressure zones. Each pressure zone has dedicated pumping stations that pump water into the zone to maintain pressure. Water towers help stabilize pressure in some zones. Water flows into the towers during hours of the day when there is less water demand and flows back out to satisfy higher demands. The combination of water from the pumping station and water flowing out of the water tower acts to stabilize pressures in the zone.
Water pressure in the Des Moines system averages 50 psi but ranges from 35 psi to more than 100 psi depending on the location in the city. Thirty five psi is Water Works Board established minimum system pressure in Des Moines. Plumbing code requires that residential properties in areas with water pressure in excess of 80 psi be protected by pressure regulators installed on the water service lines.
Older, smaller diameter service lines or corroded service line components such as valves or couplings can cause low pressure for some customers. Currently, DMWW Rules and Regulations require that new residential service lines be installed using one-inch diameter copper or cross-linked polyethylene (PEX) pipe. Historically, ¾-inch or even ½-inch pipe was used and in some cases the pipe was galvanized steel which is subject to corrosion when buried. Homes with smaller diameter service lines, especially those with ½-inch galvanized pipe service lines, may experience low pressure due to restrictions in the pipe. Galvanized steel pipe inside the home may also contribute to pressure problems as corrosion occurs on the inside of the pipes.
Customers who feel they may have pressure problems can visit with a customer service representative for more information by calling (515) 283-8700.