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I I I I I I I I I I I I I I I I I I I combination of these two would occur when the irrigation system is operated on demand, but within a fixed time window (night time hours, for instance). As with any irrigation system, the system capacity is based upon the irrigated area, application efficiency, peak season evapotranspiration, days of operation per week, and the allowable daily irrigation window. The major difference between a secondary water system to individual home sites and a larger site such as a golf course is the number of irrigation system managers involved. In the case of a golf course, for example, one irrigation manager is typically in charge of scheduling and operating the irrigation system. This allows the pump station and mainline pipe to be sized to operate at full capacity for a given window of time, say 8 hours per day. This type of user is very predictable and is represented by a relatively flat demand curve over time. The demand, and therefore the flow rate of the irrigation system, ramps up to full capacity over several minutes at the start of the irrigation window. It then runs at capacity until the demand drops off at the end of the irrigation window. By contrast, a secondary water system for a typical 80-acre housing development, or a whole community, may have 200 to 400 individual lots, in addition to common open space areas. These systems must be designed to accommodate 200 to 400 individual water managers, most of whom are homeowners who have little or no experience in operating or managing irrigation systems. One way to design and manage a secondary system for subdivisions is to impose tight irrigation watering windows for each lot. For example, Group 1 lots would only be allowed to irrigate between the hours of 10 pm and 1 am, Monday, Wednesday, and Friday. Group 2 lots would be allowed to operate between 1 am and 4 am Monday, Wednesday, and Friday, and so on. While this approach to system design can reduce the installation cost of the secondary water system and maximize pump station operating efficiency, it is generally difficult to manage and may impose overly restrictive conditions on homeowners. What often happens is that the restrictions are not clearly indicated to new homeowners by real estate agents, builders, or original homeowners when they sell the home. Over time, the rules and order can break down leading to overall homeowner dissatisfaction with the secondary water system. Irrigation systems that require users to follow very narrow operating parameters are generally only successful when there are a small number of lots or customers, such as in estate lot residential development with a very strong and active homeowner's association in place. Another approach is to design the secondary system based on lawn watering restrictions commonly imposed by potable water purveyors when potable water is used for irrigation. In Colorado, it is common to encourage homeowners to irrigate every other day, or every third day during a drought. Using this as a basis for design, the pressurized secondary water system would be designed to allow between one-half and one-third of the lots to irrigate on any given day. It is common to limit the flow from an individual residential tap to 10 gallons per minute (GPM), the typical flow allowed by systems using potable water under a typical 5/8" or Aqua Engineering, Inc. November 17,2004 Canal Modernization Study -5-