Empirical formula for pipe pressure loss.
Computes hydraulic gradient in pressurized pipes for turbulent water flow at ~15 °C. Works well in the 1–3 m/s range. We use C = 150 for PE100, 145 for PVC, 100 for galvanized steel.
h_f = 10.67 · L · Q^1.852 / (C^1.852 · d^4.87)
Pipe flow velocity sanity check.
Velocity > 2.0 m/s causes water hammer and noise; < 0.5 m/s causes sedimentation. Target range: 1.2–1.8 m/s on the main, 0.8–1.5 m/s on laterals.
v = 4·Q / (π·d²)
Pressure budget for an irrigation branch.
Total losses from the tap to the furthest head + the head's working pressure + 10–15% safety margin. Must not exceed pressure at the meter.
P_src ≥ P_head + Σh_f + h_v + h_z + 10%
Sprinkler head working pressure.
Inlet pressure at which the manufacturer guarantees rated radius, flow and precipitation rate. Hunter MP Rotator — 2.8 bar. Rain Bird R-VAN — 3.0 bar.
Reference evapotranspiration.
Evaporation from a reference surface (well-watered grass, 12 cm tall). The base input for water demand. We compute it via Penman–Monteith FAO-56 using NOAA GFS + Copernicus ERA5 data.
ETo = (0.408·Δ·(R_n − G) + γ·(900/(T+273))·u₂·(e_s−e_a)) / (Δ + γ·(1+0.34·u₂))
Crop coefficient.
Ratio of how much a specific plant evaporates relative to the reference. Cool-season lawn: 0.80; warm-season: 0.60; ornamental shrub: 0.50; mature lawn: 0.85.
ET_crop = ETo · Kc
Net water requirement.
Volume of water to add per week, accounting for rainfall and system efficiency.
I = (ET_crop − P_eff) / E_app
Split run on compacted soils.
Instead of one 30-minute run, use 3 cycles of 10 min with 30-min soak intervals. Prevents runoff on slopes and compact soils. Saves 15–25% water and avoids erosion.
Christiansen Uniformity Coefficient.
Measure of irrigation uniformity from a grid of measured doses. CU 85% is the ASABE S441 'good' threshold; 90%+ is professional grade. Computed from dry-can tests.
CU = 100·(1 − Σ|x_i − x̄|/(n·x̄))
Distribution Uniformity, low-quarter.
Ratio of average dose in the driest 25% of points to the overall mean. Stricter than CU. DU > 0.75 is good. Used by agronomists and LEED certification.
DU = x̄_lq / x̄
Water application efficiency.
Share of delivered water that actually reaches the root zone. Spray + light wind: 60%; rotor: 70%; drip: 90%; subsurface drip: 95%.
Irrigation intensity.
Millimetres of water deposited per unit area per hour. Critical input for runtime computation. Spray heads: 35–50 mm/h; rotors: 10–18 mm/h; MP Rotator: 10–11 mm/h.
PR = 60·Q / A
Hunter multi-stream nozzle.
Multi-stream rotary nozzle with low precipitation rate (10–11 mm/h) and high CU. Operates at 2.8 bar. A drop-in replacement for traditional spray on pop-up bodies.
Rain Bird rotary nozzle.
Rain Bird's MP Rotator analogue. Adjustable arc 45°–270° / 360°. Radius 2.4–4.6 m (1300) or 4.0–7.6 m (1800). Good wind resistance.
Hunter commercial controller.
Programmable controller for 8/14/22/38 zones. Supports weather sensors, Solar Sync, flow monitoring and Hydrawise (Wi-Fi). Standard pick on commercial projects.
Rain Bird residential controller.
Modular 4/8/12/22-zone controller. LNK Wi-Fi module, ET-based scheduling. Alternative to ICC2 for residential and small commercial sites.
Hunter ET-based adjustment.
Solar radiation + temperature sensor that automatically tunes runtime to actual ET. Saves 30–40% water versus a fixed schedule.
System-level shut-off valve.
Solenoid valve at the supply that closes when no zone is active. Protects against leaks if a lateral is damaged. Mandatory on commercial projects.
Soil water infiltration speed.
Millimetres of moisture the soil can absorb per hour without runoff. Depends on type: sand 25 mm/h; sandy loam 18 mm/h; loam 12 mm/h; clay 5 mm/h.
Field capacity.
Water held by the soil against gravity 24–48 h after saturation. Upper bound of readily-available water. Expressed as %vol.
Permanent wilting point.
The lowest moisture content at which a plant can still survive. Lower bound of readily-available water. Typically at ψ = -1500 kPa.
Standard for sprinkler distribution.
American Society of Agricultural and Biological Engineers — protocol for measuring CU/DU/PR via field catch-can tests. Baseline for manufacturer certification.
French irrigation standard.
Norm for design and operation of irrigation systems in France and most francophone countries. Accounts for Mediterranean and Atlantic climates.
Ukrainian water-supply standard.
Internal water-supply systems — the basis for hydraulic calculations in Ukraine. Compatible with SNiP 2.04.01-85 for the transition period.
European sprinkler standard.
European norm for sprinkler systems in landscape irrigation. Regulates materials, fittings, marking and catch-can test requirements.