Irrigation main for a subdivision

Discussion in 'Irrigation' started by KSTreeguy, Mar 25, 2008.

  1. KSTreeguy

    KSTreeguy LawnSite Member
    Posts: 4

    Howdy...I've been a lurker for a while and now have a dilemma I could use some advice on.

    I've been asked by a development client to design an irrigation mainline for a new development...69 residential lots on about 45 acres with each lot tapping into this main w/ 1" connections off of the main (as opposed to individual wells on each property). The system will be served by groundwater, so I'm going with a constant pressure system with variable speed well pumps. I've got good groundwater source (12' deep w/ drawdown to about 30' per a local driller). The system is going to be looped and we've made the decision to place 4-5 wells on the system, spread across the system (approx 7000 LF of pipe), to lower pipe size and distribute the supply across the development.

    The problem I face is the number of wells and matching demand. I've assumed about 12GPM demand for each lot (based on average well production in the area), so worst case scenario, we're talking about 830 GPM usage for all 69 lots total. The local driller I've talked to has recommended 10 HP, 3-phase pumps that are capable of about 180 GPM, hence why we're looking at 4-5 wells. However, not everyone will water at the same time thereby spreading demand. Is sizing the system and pumps based on that worst-case scenario the most prudent/ economical thing to do, or is there another, better way to do it?

    Disclaimer: I've designed irrigation systems before, however, this is the largest I've done to date. I've talked to some friends locally on the contractor side and they didn't seem too concerned, but I'm still nervous about the size and number of pumps and how that affects my pipe sizing.

    Clear as mud? Thank you for any advice you all can provide.
  2. Mike Leary

    Mike Leary LawnSite Fanatic
    Posts: 22,142

    Nice to see a lurker come out of the closet, welcome to design insanity.
    This should be a interesting thread as only a few of us have ever gotten close to this type of system. It's the well supply system you need to know,
    big time....drawdown...recharge. Check back when the numbers come up.
  3. BrandonV

    BrandonV LawnSite Platinum Member
    Posts: 4,303

    how are you going to ensure not all systems come on at the same time? assigning days?
  4. Like Mike said design the system around the drawdown and recharge rate of the wells....
  5. Mike Leary

    Mike Leary LawnSite Fanatic
    Posts: 22,142

    You'll want to draw from all the wells, at different times, depending on re-charge.I'd be looking at central system..Calsense, Rain Master.
  6. KSTreeguy

    KSTreeguy LawnSite Member
    Posts: 4

    I think the usage issue will have to be addressed by the developer, maybe in the covenants...maybe by assigning days in which you can and can't water (odd numbered addresses on odd days, etc). I'm not sure if he grasped how complex this will be (just told us to "throw in some 3HP pumps to make sure we have good flows).
  7. Mike Leary

    Mike Leary LawnSite Fanatic
    Posts: 22,142

    How about monster complex?
  8. I manage a community wide system that has 69 homes and has 120+ zones running off two water meters. Some areas run off two central controllers and 16 homes have their own controllers. The system has 2 master valves on the central controllers and I do a lot of run time calculations, so the master valves will stay open for the 16 independent controllers. I have a 30%, 60%, 90% and 100% schedules for the changing off the seasons. Total run time for one complete cycle is 21 hrs....
  9. Mike Leary

    Mike Leary LawnSite Fanatic
    Posts: 22,142

    We have one that runs 24-7 during the season...gotta be on the programming.
    Percentages are a great way to run systems.
  10. Wet_Boots

    Wet_Boots LawnSite Fanatic
    Posts: 48,330

    I could see each lot connected to the main with a master valve that is enabled from a central computer, making odd-even-day-watering compliance automatic. Maybe even flow limiting could be built in.

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