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Estimate subsurface drain spacing using a simplified Hooghoudt approach, then compute total tile length and installation cost for your field.
Enter hydraulic conductivity (m/day), drain depth, drainage coefficient (mm/day), field area and installation cost per meter. The calculator returns drain spacing, total length, total cost and cost per hectare.
Your poorly drained 10 ha field sits waterlogged in spring. The drainage contractor proposed 20 m spacing at $5/m, but your soil K is only 0.5 m/day. With that spacing the drains will not remove water fast enough — you need 10 m spacing and the cost doubles.
✓ Expert Reviewed: This calculator and its content have been reviewed by agricultural experts. Formulas are based on standard extension service recommendations. For site-specific advice, consult your local agronomist.
Estimate hydraulic conductivity from your soil type (sands 2–5, loams 0.5–2, clays 0.1–0.5 m/day). Set drain depth (typically 0.9–1.2 m), drainage coefficient (10–15 mm/day for row crops), field area and local installation cost. Click Calculate.
This calculator uses a simplified Hooghoudt steady-state equation: S = sqrt(4 × K × (2d² − 0.5d²) ÷ q), where K is hydraulic conductivity, d is drain depth, and q is drainage coefficient in m/day. Spacing is in meters. Total tile length = field area (m²) ÷ spacing.
Convert q from mm/day to m/day (÷ 1000). Spacing S = sqrt(4 × K × 1.5 × d² ÷ q). Total length (m) = area (ha) × 10,000 ÷ S. Total cost = total length × cost per meter. Cost per hectare = total cost ÷ area.
K = 1.0 m/day, d = 1.0 m, q = 10 mm/day = 0.01 m/day. S = sqrt(4 × 1 × 1.5 × 1.0 ÷ 0.01) = sqrt(600) ≈ 24.5 m. For 10 ha: total length = 10 × 10,000 ÷ 24.5 ≈ 4,082 m. At $5/m: $20,410, or $2,041/ha.
Common mistakes: using K for the topsoil when the limiting layer is deeper, installing drains too shallow (< 0.9 m), choosing a drainage coefficient that is too low for row crops (use 10–15 mm/day), and forgetting outlet and maintenance costs (trenches, mains, risers). Always map the outlet location before designing.
Typical spacings are 10–15 m in heavy clays, 15–25 m in loams, 25–50 m in sandy soils. Spacing depends on soil permeability and desired water-table drawdown within 24 hours after a rain. This calculator computes it from K, depth and drainage coefficient.
Laterals are typically installed at 0.9–1.2 m depth. Shallower than 0.9 m risks freezing and root damage; deeper than 1.5 m makes installation costly and does not improve drying much. The main drain should slope 0.1–0.3% toward the outlet.
The drainage coefficient (DC) is the rate, in mm/day, at which the water table must be lowered after a storm. Row crops typically require 10–15 mm/day; vegetables and high-value crops 15–25 mm/day. A higher DC dries the field faster but costs more in tile.
Typical installation costs range $4–$10 per meter of tile, plus mains, risers and outlet structures. For 10 m spacing at $5/m on loam, cost is about $2,000–$2,500/ha. ROI is typically 5–10 years through earlier planting, higher yields and reduced compaction.
Yes, on poorly drained soils. Tile drainage extends the planting window (you can work the field sooner in spring), reduces root-zone saturation, improves soil aeration, and allows earlier field operations. Yield gains of 10–30% on poorly drained cropland are typical in the first few years.