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Drainage Tile Calculator
Estimate subsurface drain spacing using a simplified Hooghoudt approach, then compute total tile length and installation cost for your field.
Results
How to Use This Calculator
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.
About This Tool
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.
Applicability: Designed for farm equipment and energy planning in North American and European contexts.
How the Calculation Works
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.
Real-World Example
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 & Tips
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.
Reviewed by Agricalc Editorial Team — Agricultural engineers and agronomists with 10+ years of field experience. Our team verifies every calculator formula against peer-reviewed extension publications. For site-specific advice, consult your local agronomist.
References
- USDA NRCS — Agricultural Drainage
- University of Minnesota Extension — Agricultural Drainage
- FAO — Drainage Design
Frequently Asked Questions
How far apart should drainage tiles be?
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.
How deep should drainage tile be?
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.
What is a drainage coefficient?
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.
How much does tile drainage cost?
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.
Will tile drainage improve my yields?
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.
