Planning Irrigation and New Turf

One Valve, One Rate

A zone waters on a single clock. Every head on that valve opens together, shuts together and runs the same number of minutes, so the only way each square metre of turf receives the same depth of water is for every head to apply it at the same rate. Precipitation rate — millimetres or inches of depth applied per hour — is not a figure you look up after commissioning. It is the specification the zone is built to, and head selection, spacing, valve grouping, pipe sizing, controller programming and even the finished grade either serve that number or quietly fight it for the life of the system.

Mixing head families on one circuit is the failure that never heals. Fixed sprays lay water down several times faster than gear-drive rotors; put both on one valve and no run time exists that satisfies either. Long enough for the rotors and the spray ground sheets water across the hard edge, waterlogs the rootzone and goes anaerobic. Short enough for the sprays and the rotor ground burns out in the first heatwave. The client then does what clients do — adds minutes until the dry patch greens up — and the wet end stays wet all season.

Arc is the second trap, and it hides better. A half-circle nozzle covering half the area of a full circle must discharge half the flow to apply the same depth; if the nozzle set is not built for that, corners and edges drift out of step with the middle of the lawn even though every head looks identical from the path. Matched-rate nozzle families exist precisely for this, and ASABE/ICC 802, Landscape Irrigation Sprinkler and Emitter Standard, gives the reference frame under which manufacturers publish the data that lets you compare one family against another. Getting it wrong is not a tuning problem later. It is a trenching problem, under turf that has already knitted.

What the Supply Will Actually Give You

Design starts at the point of connection with a gauge and a bucket, not with a head layout. Static pressure tells you little on its own; what matters is dynamic pressure at the flow you intend to draw, measured with water moving, because meter losses, service line size, the backflow assembly and every fitting between there and the last head come out of the same budget. Undersized service pipe is the usual culprit behind a system that tested beautifully on one zone and misted its way through August once the schedule stacked zones back to back.

Soil sets the other ceiling, and it is the one people skip. A zone can be perfectly matched at forty millimetres per hour and still fail on a heavy clay that accepts a small fraction of that, because water applied faster than the soil takes it does not become deeper irrigation — it becomes runoff, or a puddle at the low corner. Intake rate falls further as the profile wets, and falls again on slope. High-rate zones on tight soils have to be pulsed: short cycles with soak periods between them, totalling the required depth.

Slope, aspect and shade change demand rather than rate, and those are different problems with different fixes. A south-facing bank and a shaded north strip need different run times, which means different valves — no nozzle change rescues a zone that spans both. Write the measured dynamic pressure, the available flow with margin, and the soil intake estimate onto the plan itself; those three numbers constrain every zone you are about to draw.

Grouping Heads So the Rate Survives the Plan

Zoning turns the abstract constraint into valve count. Heads group by family first, then by hydrology and exposure: turf apart from beds, spray apart from rotor, rotary nozzles apart from both, full sun apart from deep shade, top of slope apart from toe. Each of those splits exists because a group shares one run time, and anything needing a different run time needs a different valve.

Flow discipline runs alongside. Sum the published nozzle discharge for every head you intend to put on a valve, add losses through the lateral and the valve itself, and keep the total inside the available flow with headroom — laterals are commonly designed to a velocity ceiling near 1.5 m/s (5 ft/s) to hold friction loss and surge in check. A zone squeezed to the edge of the supply behaves exactly like a zone with a pressure fault: far heads under-throw, near heads over-throw, and the matched rate you designed exists only on paper.

Count valves honestly at this stage. Adding a solenoid, a valve box and a wire run during layout is trivial next to splitting a zone after the turf is down, and the split people postpone is almost always the one between sun and shade.

Spacing, Arc and Wind Decide Whether the Rate Is Real

Head-to-head coverage is the baseline: throw reaches the adjacent head, so every point sits under at least two patterns and the single-head profile — always heaviest near the head — averages out. Spacing gets specified as a percentage of the manufacturer's published radius at the design pressure, and that percentage tightens as wind rises. Site wind governs, not a generic allowance; work from the manufacturer's spacing chart and derate for the conditions the lawn sees at the hours you plan to irrigate.

Uniformity is measurable, and in awkward geometry the measure matters more than the headline rate. Distribution uniformity computed from the low quarter of a catch-can grid tells you what the driest ground receives; ISO 15886-3, Agricultural irrigation equipment — Sprinklers — Part 3: Characterization of distribution and test methods, sets out how sprinkler distribution is characterised under test. Poor uniformity forces you to over-water the whole zone to keep the worst patch alive, which is how a matched-rate system still doubles a water bill.

Narrow strips, tight corners and long verges deserve their own treatment. Strip and side-strip nozzles carry their own rates and rarely match the circular family around them; hanging one off a turf valve to save a solenoid reintroduces the mismatch the zoning was meant to prevent. Triangular spacing beats square for uniformity on open ground, while square lays out more easily against a boundary and is often the honest choice on a small rectangle.

Pressure Drift and the Slow Failures

Nozzle discharge is a function of pressure, so pressure variation across a zone is rate variation under another name. Elevation alone accounts for roughly 0.1 bar per metre of rise (about 0.43 psi per foot), and a zone running up a bank loses that from the top heads while the bottom heads sit over-pressured. Pressure-regulating stems or in-line regulation bring the whole zone back to a common working pressure; without them the crest under-applies and the toe mists.

Misting is the visible symptom of over-pressure and the expensive one — droplets fine enough to drift never reach the ground the zone was scheduled for, so the depth you calculated is not the depth delivered. Under-pressure produces the opposite signature: a ring of dry turf around each head where the pattern collapses inward. Both read as uneven watering to the client, and both get blamed on the nozzles.

Low-head drainage finishes the picture on any sloping job. Without check valves the lateral empties through the lowest head after every cycle, flooding one patch and forcing the zone to re-pressurise and blow air through the pattern at the next start. Specify check valves in the heads or in the lateral, and put the drainage point somewhere it can be seen and reached.

Drip and Rotary Nozzles Are Separate Rate Classes

Inline dripline applies water at a rate set by emitter discharge, emitter spacing and lateral spacing together, typically an order of magnitude below a spray zone, and it shares no useful schedule with anything else. Give it a dedicated valve, always, with filtration and pressure regulation at the head of the zone — emitters plug quietly, and the first symptom is a dead plant rather than a visible fault.

Flush points at lateral ends, air and vacuum relief at high points, and a visible operation indicator are not optional extras on subsurface work; a buried zone nobody can see running gets ignored until the planting fails. Rotary and stream-type nozzles occupy the middle ground: low application rate, good behaviour on slopes and tight soils, long run times to compensate. That advantage disappears the moment one shares a valve with a fixed spray.

Turf and Grade Have to Fit Inside the Rate

New sod and new seed want opposite things from a schedule, and the zone has to serve both in sequence. Freshly laid turf needs frequent light applications to keep the sod-to-soil interface damp until roots knit, then a deliberate taper toward deeper, less frequent cycles that pull roots down. A high-rate spray zone over clay cannot deliver light frequent water without ponding along the seams unless it is cycled, so the establishment programme belongs on paper before the turf arrives rather than improvised on delivery day.

Grade governs whether any of it drains. Finished soil level has to sit below adjacent paths, kerbs and beds by the full thickness of the sod plus its soil, or the new lawn stands proud, sheds water onto the hard surface and scalps on the first mow. Rootzone depth, decompaction and the fall away from structures all get resolved before heads go in — trenching after grading beats grading around heads.

Delivery timing is unforgiving. Harvested turf heats on the pallet and deteriorates fast in warm weather, so the order has to be sized correctly the first time and laid promptly; Turfgrass Producers International's Guideline Specifications to Turfgrass Sodding covers the handling and installation expectations most specifications lean on. Order against the measured area with allowance for curved edges and seam offsets — offcuts are waste, and coming up short strands a crew mid-lay with the light going.

Catch Cans Prove the Rate; Nothing Else Does

Commissioning turns a design number into a measured one. Set identical catch cans on a regular grid across the zone, run for a fixed period, then measure each volume — the average gives delivered precipitation rate, and the mean of the lowest quarter against that average gives distribution uniformity. Published nozzle figures are laboratory figures at a stated pressure; the grid tells you what your pressure, your spacing and your wind actually produce on this lawn.

Walk each zone twice before touching the controller. First pass: arcs set to the boundary and not onto the driveway, radii adjusted, nozzles matched to arcs, risers plumb, heads at grade so a mower passes over them. Second pass with a gauge on the first and last head confirms the zone holds working pressure end to end. Correct hardware first, then set run times from the measured rate and the target depth.

Programming carries the constraint into daily operation. Cycle-and-soak splits any zone whose measured rate outruns the soil's intake, seasonal adjustment scales the whole programme against demand instead of editing every zone by hand, and rain or soil-moisture sensors are mandatory in many jurisdictions — the local water purveyor and adopted plumbing code decide which. Leave the measured rate and target depth written inside the controller door where the next person will find them.

Backflow, As-Builts and a Handover That Holds

Cross-connection protection is code work, not design preference. Which assembly the job requires — reduced pressure principle, double check, or pressure vacuum breaker, described respectively by ASSE 1013, ASSE 1015 and ASSE 1020 — is set by the local plumbing code, the adopted model code such as the International Plumbing Code or the Uniform Plumbing Code, and the water purveyor's own rules; many jurisdictions also require testing by a certified tester at installation and annually thereafter. Confirm that requirement in writing before ordering the assembly.

Paperwork closes the job. An as-built showing valve boxes dimensioned from two fixed points, wire routes, spare conductors at each box, mainline depth and the point of connection saves a long afternoon on the first repair call. Beside it, a zone schedule listing head family, nozzle set, measured precipitation rate and commissioning run times hands whoever inherits the system the one thing they cannot reverse-engineer from the ground: the rate each valve was built to deliver.