PROJ02008

• Contract/PO #: FS0073FX
• Contractor Name: Lamar, City of
• Contract Type: Grant
• Water District: 0
• Loan Projects - Doc Type: Feasibility Study

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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 watering restrictions in subdivision covenants 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.

Figure 9 and 10 show a typical point of connection detail for a raw water connection at a
residential lot or at other discrete open space areas such as parks or streetscapes. It is
common to limit the flow from an individual residential tap to 10 GPM, the typical flow
allowed by systems using potable water under a typical 5/8" or %" water meter. Sizing a
secondary water system to allow the simultaneous operation of half of all irrigation
services in a typical development consisting of 7 ,000 square foot lots is very
conservative, and generally results in excessive pump station capacity and distribution
pipe sizing

Whichever method is used for estimating peak flow, the pump station and distribution
system must be sized to accommodate the peak flow. Hydraulic network analysis
software is very useful in analyzing pipe sizing for secondary systems. Typically, the
distribution pipe is sized to keep velocities below 5 feet per second. In many instances

3 It is interesting to note that a larger 1-inch tap and somewhat higher flow rate of 20 GPM is
desirable for the homeowner because system cost is less due to fewer valves, less wiring, and a
smaller controller. Taken together the cost of the irrigation system can be substantially less for a
larger available flow.
Aqua Engineering, Inc.
and Colorado State University Secondary Supply Feasibility Study
May 19, 2004 -4-