Friedman et al. Increasing sizes of pigs are passed through the pipeline to gradually remove deposits within the pipeline. For example pipe roughness, which affects water flow and residence time, may be modified by repair or rehabilitation. The amount of data collected is determined by the polling frequency of the SCADA system. Denver, CO: AwwaRF. Water Resources Planning and Management 122(1):11–19. Water age at a given location and time in a water distribution system is actually a mixture of water parcels that have traveled along different paths through the distribution system with correspondingly different travel times. Maintaining the hydraulic integrity of distribution systems is vital to ensuring that water of acceptable quality is delivered in acceptable amounts. 2003. Scrapers are devices that use springs to force blades against the wall of the pipe. One of the first steps is to consider one or more of the standard techniques available to remove any loose sediment, biofilm, and tubercles that may be the cause of the problem. For most water systems the ratio of the maximum day water demand to the average day water demand ranges from 1.2 to 3.0, and the ratio of the peak hour to the average day is typically between 3.0 and 6.0. For example, extreme fluctuations in pressure and flow readings could result from pressure surges generated from a power failure at a pump station. MAINTENANCE AND REHABILITATION/ REPLACEMENT, Chapter 18: Modeling, analysis and design of water distribution systems. A combination of devices may prove to be the most effective and economical. (2000) used various modeling techniques to develop a set of general guidelines for reducing water quality deterioration associated with inadequate mixing and excessive water age in distribution storage facilities. This report evaluates approaches for risk characterization and recent data, and it identifies a variety of strategies that could be considered to reduce the risks posed by water-quality deteriorating events in distribution systems. Flushing (discussed in greater detail in a subsequent section) is performed by isolating sections of the distribution system and opening fire hydrants (or flushing valves) to cause a large volume of flow to pass through the isolated pipelines so that a scouring action is created. ground movement). For example, the North Marin Water Authority in North Marin, California, draws its water from two sources, one of very poor quality with high levels of natural organic matter and another source of very high quality. While more costly and time consuming than conventional flushing, unidirectional flushing is more effective and uses less water (Hasit et al., 2004). There is now greater recognition of the water quality effects of how long water is retained in the various elements of the distribution system. Excessive residence times can lead to low disinfectant residuals and leave certain service areas with a less protected drinking water supply. The effects of internal corrosion, shown as a build up of tuberculation, on an unlined cast iron water main. An effective system-wide monitoring program can capture local variations in hydraulic behavior (e.g., pressure, flow) at a specific point in a water distribution system but cannot provide an overall understanding of the spatial and temporal changes, complex flow pathways, and interactions among the various water system characteristics. Intrusion within a simulated water distribution system due to hydraulic transients. Boulos et al. This is a prime location for intrusion to occur in the event of low or negative pressure transients. This, in turn, may lead to serious water quality problems, some of which may threaten public health. Cesario, L. 1995. Unidirectional flushing involves the closure of valves and opening of hydrants to create a one-way flow in the water mains (see Figure 5-5). (2006). These predictive capabilities are useful for detecting a loss of system hydraulic integrity. Because of demand variations there is a great deal of mixing between the water sources at various nodes in the system leading to wide variations in trihalomethane (THM) values over a given day. Hydraulic modeling, discussed in the previous section, is also a critical component that can be used to identify problems areas within the distribution system and to develop design and operational alternatives that address the deficiencies. The data generated from the sensors and transmitters is conveyed to the central control system using various communication media such as telephone lines, fiber optic cables, or radio and cellular systems. On the surface these variations in THM concentration were unexplainable until hydraulic modeling techniques were applied which clearly showed that these variations were the result of the mixing effect from the two sources of water (Clark and Buchberger, 2004). Most systems require pumps to supply lift to overcome differences in elevation and energy losses caused by friction. Pressure zone boundaries are delineated through the use of closed valves. OPTIMAL DESIGN OF WATER DISTRIBUTION SYSTEMS, Chapter 8: AWWA. 97(5):111–124. 2004. Spray-on epoxy lining is a newer method that is especially useful when the water is low in hardness, which can cause a cement lining to deteriorate. 1996. © 2006 by MWH Soft Pub. All these activities can result in a reduction in system capacity and supply pressure and changes to the flow paths of water within the distribution system. 2005. water hammer) or external threats (e.g. The deposition of corrosion products in the form of tubercles and other types of scales on the interior of the pipes can seriously clog water lines and thus restrict the flow of water. Excessive pressure surges generate high fluid velocity fluctuations and may cause resuspension of settled particles as well as biofilm detachment. Examples include looping of the pipe network and the development of backup sources to ensure multiple delivery points to all areas. The three concentration peaks represent the different parcels of water that have taken different routes to the monitoring point, resulting in a residence time distribution at that monitoring station at the time the data were collected. Marshall, G. P. 2000. Good maintenance, pressure management, an adequate disinfectant residual, and routine monitoring programs are also essential components of transient protection. The general principles of pressure surge control devices are to store water or otherwise delay the change of flow or to discharge water from the line so that rapid or extreme fluctuations in the flow regime are minimized. When water is moving slowly through a pipe, particles suspended in the water may settle out into the pipe. A fire-flow demand or large water use on a dead-end main can only draw water through a single pipe, with the maximum flow dictated by the size and length of the pipe. For example, in Blacksburg, Virginia, 97 percent of the water in the main distribution system has a water age of less than 7 days, but 1 percent of the system has a residence time longer than 28 days.