The 15-Minute Schedule: Auditing a Four-Zone Ocala System Under Restrictions
A 22,000 sq ft 'Floratam' St. Augustine lawn on a 1.2-acre residential lot in Ocala is split into four equal irrigation zones. Each zone has 14 pop-up spray heads with 3.0 gpm nozzles. Static pressure at the backflow preventer is 62 psi, and the well supplies water with 1.8 ppm iron. The controller runs Monday, Wednesday, and Friday at 4:30 a.m. for 15 minutes per zone. There is no rain sensor. The owner complains of dry, wilted turf along the concrete driveway and of water sheeting across the sidewalk into the street after about six minutes of run time. A catch-can audit on zone 2 for 30 minutes gave 0.22, 0.55, 0.30, 0.48, and 0.25 inches in five cans. The county is under a once-per-week irrigation restriction, and the property is on a community well shared with three neighbors.
1. Using the audit data, calculate the precipitation rate and distribution uniformity for zone 2 and determine the correct weekly run time.
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Work the numbers rather than guessing at run times.
Application rate. Zone 2 covers 5,500 sq ft (22,000 ÷ 4). Flow is 14 heads × 3.0 gpm = 42 gpm. Precipitation rate = (96.25 × gpm) ÷ sq ft = (96.25 × 42) ÷ 5,500 ≈ 0.74 in/hr. Over 30 minutes that is about 0.37 in, which matches the can average: (0.22 + 0.55 + 0.30 + 0.48 + 0.25) ÷ 5 = 0.36 in. The audit is internally consistent.
Distribution uniformity. Low-quarter DU = lowest can ÷ average can = 0.22 ÷ 0.36 ≈ 0.61. Anything below roughly 0.70 means the zone applies water unevenly, and some turf receives far less than the average.
Run time. Use the low-quarter rate, not the average, or the dry spots stay dry. Low-quarter rate = 0.22 in per 30 min = 0.44 in/hr. For a 0.5-inch weekly target: 0.5 ÷ 0.44 ≈ 1.14 hr ≈ 68 minutes per zone per week. Under a once-weekly restriction that is one 68-minute application, but this soil will not absorb it in a single pass - split it into four 17-minute cycles with about an hour between cycles.
For comparison, the current schedule applies 0.74 × 0.25 hr × 3 days ≈ 0.55 in/week on paper, but at DU 0.61 the dry can is getting roughly 0.34 in - which is exactly why the lawn looks under-watered while the owner believes he is watering heavily.
2. Diagnose the runoff after six minutes and the dry strip along the driveway, and prioritize the corrective actions.
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Runoff after six minutes is an infiltration and hardware problem, not a scheduling problem.
- Check the obvious first. Walk the zone with water running. A broken riser, a tilted or sunken head, a nozzle missing its filter screen, or a head spraying directly onto concrete will all produce what the owner describes. A 3.0 gpm nozzle that has lost its screen can discharge well above its rated flow - that alone explains water sheeting across the sidewalk.
- Match heads to spacing. A pattern of 0.55 in in one can and 0.22 in in another usually means spacing is inconsistent with the nozzle. Measure actual spacing; if any heads sit 18–20 ft apart with spray nozzles rated for 15 ft, replace with matched-precipitation nozzles sized to the real spacing, or convert the zone to rotors or multi-stream rotators, which apply water more slowly and infiltrate better on a compacted berm.
- Fix infiltration. After years of traffic the soil along the drive is likely compacted with an accumulating thatch layer. Core aerate, topdress, and keep thatch under 1/2 inch; use cycle-and-soak until the soil recovers.
- The driveway edge. Pavement stores and reflects heat, so that strip wilts first. Confirm the heads actually throw to the concrete edge - a one-foot dry gap is a spacing failure, not a water shortage. A dedicated edge zone or drip line plus 2–3 inches of mulch kept off the turf does more than lengthening the whole zone.
Order of work: hardware and nozzle correction first, then aeration and thatch, then the new schedule. Adding time to a broken zone just wastes water faster.
3. What compliance and water-quality obligations apply to this system, and what would you put in writing to the owner?
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Several requirements stack here, and none of them disappear because the water comes from a community well.
- Rain sensor or shutoff. Florida Statutes section 373.62 requires an automatic irrigation system to have a functioning rain sensor or other shutoff device so the system does not operate during or after sufficient rainfall. This system has none - install one and test it at every service visit. Some jurisdictions also require soil-moisture sensors on new installations.
- Once-per-week restriction. The county limit controls the schedule regardless of what the controller will allow. Program one day per week and document the setting so the owner cannot blame you for a violation.
- Controller. Move to a seasonal-adjust or smart schedule with run times derived from the audit - roughly 68 minutes per zone in one day, split into cycles - rather than a fixed 15 minutes year-round.
- Well water quality. 1.8 ppm iron stains concrete, siding, and pool decks, and can clog nozzles and filters. Fit a filter, flush laterals at the start of each season, and avoid irrigating hardscape and fencing with well water. Because the well is shared, coordinate any long run times with the neighbors so you do not draw down pressure.
- Documentation. Leave a written audit summary, the new schedule, the sensor test result, and a note that additional time was not added because the problem was uniformity, not volume.