Rural Water - Quarter 1, 2009 - (Page 35)

in the older part of the system on the hill? • Do I have sufficient pressure and availability at the fire hydrant at Hilltop Elementary School? The calculations necessary to support these answers are generally too large and complicated to perform by hand. Over the years, more and more utilities have turned to hydraulic computer models to support their asset management decision making. Once, these models were so complex and difﬁcult to use that they were mainly used by large utilities and their consultants. Now, competition and technology advances have driven costs down and the models are so easy to learn and use that even the smallest water utilities can afford them (or can’t afford not to have them!). More and more regulators are insisting on seeing the results of model runs before they approve system improvements. What is a computer model? At the heart of any model is a numerical computer program that solves equations. There are basically two types of equations that must be solved in any hydraulic calculations: 1. Mass continuity (conservation of mass) equation a. Flow rate of water into any junction of pipes equals ﬂow out; and, b. For any tank, ﬂow in minus ﬂow out equals change of volume in storage. 2. Energy equation – water gains or loses energy as it moves through a distribution system a. Losing energy due to friction/roughness as it moves through pipes; b. Gains energy as it passes through pumps; and, c. Loses energy as it passes through valves. These equations are not terribly difﬁcult to solve except that there is not a single energy equation or a single continuity equation. Instead, there is one continuity equation for every pipe junction or tank and one energy equation for every pipe. This means that to solve the network hydraulics, the computer must solve hundreds or thousands of equations simultaneously – not something you want to do by hand. Solving all those equations gives the model user a good idea of what is happening in their system at a point in time (much like a snapshot). It is usually referred to as a steady model and in many cases, that is all one needs. However, water systems are dynamic, with pumps turning on and off through the day as demands vary. Models can track these gradual changes over time in what are usually called extended period simulation (EPS) runs. These are especially helpful in understanding system operation. In addition to gradual changes in conditions, sudden changes in pump operation or valve status can trigger transient (water hammer) events that can damage Continued on page 38 Over the years, more and more utilities have turned to hydraulic computer models to support their asset management decision making. Figure 3: Water pipe network from WaterGEMS software exported to Google EarthTM Figure 4: Water asset management for day-to-day operations First Quarter 2009 • 35

Table of Contents Feed for the Digital Edition of Rural Water - Quarter 1, 2009

Rural Water - Quarter 1, 2009 Contents From the President Question & Answer: Water Conservation in the Home Avoiding the Humpty Dumpty Approach to Data Backup From the CEO What the Future Holds Asset Management for Small Communities Understanding Your Surface Water Source: The Rivers Hydraulic Models Expeditionary Water Packaging System Graces Delta The Rural Water Rally in April Training in Hawaii Regulatory Update Rural Water Releases Report on Water Infrastructure Projects and Economic Stimulus Legislation Throwing My Loop Advertisers.com Index to Advertisers

Rural Water - Quarter 1, 2009

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