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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />%" water meter3. Sizing a secondary water system to allow the simultaneous operation <br />of half of all irrigation services in a typical development consisting of 7,000 square foot <br />lots is very conservative, and generally results in excessive pump station capacity and <br />distribution pipe sizing. <br /> <br />Whichever method is used for estimating peak flow, the pump station and distribution <br />system must be sized to accommodate the peak flow. Hydraulic network analysis <br />software is very useful in analyzing pipe sizing for secondary systems. Typically, the <br />distribution pipe is sized to keep velocities below 5 feet per second. In many instances <br />secondary water systems are installed in phases and some upsizing of pipe may be <br />required to accommodate future project phasing. <br /> <br />The irrigation pump stations must be designed to provide consistent pressure over a <br />wide variation in flow. Pump stations with variable frequency drives (also know as VFD <br />pumps) are typically utilized because of the operational flexibility that VFD stations <br />afford. A VFD pump station can be programmed to maintain a set pressure throughout <br />the pipe network, regardless of flow variations. Additionally, the VFD is more energy <br />efficient than a constant speed pump because the power draw changes based on the <br />actual need of the motor. <br /> <br />A typical system pumping water from a storage pond will include a pond intake screen, <br />intake pipe, wet well, multi-pump prefabricated pump station, and automatic self- <br />cleaning filter. Generally, a two or three pump system is adequate. However, three or <br />four main pumps are provided on large secondary water systems, or where redundant <br />pumps are required to meet specific owner requirements. <br /> <br />Where possible, the existing diversion structure and headgate that has historically been <br />in place to control the delivery of water for agricultural use can be maintained and kept in <br />place for the secondary water system as well. However, frequently the existing diversion <br />does not work with the site layout and grading. In these instances, a new diversion <br />structure, headgate, flow measurement structure, and diversion ditch or pipe may be <br />required. In some cases, pumps are required to lift water from the diversion structure to <br />a storage pond. The lift pumps must be capable of diverting water to the storage pond <br />within the constraints imposed by the ditch company. For example, the lift pumps may <br />have to be designed to pump at the same delivery flow rate that historically was used <br />with the gravity diversion system. <br /> <br />Figure 2 is a conceptual pressurized transmission system, at full build-out, for a canal <br />company that is experiencing rapid urbanization. The design and operational criteria <br />discussed above were used to conceptualize the water storage ponds, pump stations <br />and pipelines for this canal service area. <br /> <br />3 It is interesting to note that a larger 1-inch tap and somewhat higher flow rate of 20 GPM is <br />desirable for the homeowner because the individual cost of the system is less due to fewer <br />valves, less wiring, and a smaller controller. Taken together the cost of the irrigation system can <br />be substantially less for a larger available flow. <br /> <br />Aqua Engineering, Inc. <br />November 17, 2004 <br /> <br />Canal Modernization Study <br />-6- <br />