Drain Spacing Calculator
With K = 0.5 m/day, a 0.6 m water-table head, a 2 m equivalent depth and a 5 mm/day drainage coefficient, drains should be 33.2265 m apart.
Hooghoudt’s equivalent depth for the drain radius and spacing.
33.2264954516723 m
Full answer, then cut to fewer decimals (not rounded):
- 33.2264954516723 m
- 33.226495451672 m
- 33.22649545167 m
- 33.2264954516 m
- 33.226495451 m
- 33.22649545 m
- 33.2264954 m
- 33.226495 m
- 33.22649 m
- 33.2264 m
- 33.226 m
- 33.22 m
- 33.2 m
- Flow below drain level (8K₂dh)
- 4.8 m²/day
- Flow above drain level (4K₁h²)
- 0.72 m²/day
Step-by-step solution
- L² = (8K₂dh + 4K₁h²)/q = (4.8 + 0.72) ÷ 0.005 = 1104 m²
- L = 33.22649545 m
Drain Spacing Formula
L² = (8K₂ d h + 4K₁ h²) / q
d equivalent depth, h water-table height midway, q drainage coefficient
Worked Example
K = 0.5 m/day above and below drains, h = 0.6 m, d = 2 m and q = 5 mm/day:
- L² = (8K₂dh + 4K₁h²)/q = (4.8 + 0.72) ÷ 0.005 = 1104 m²
- L = 33.22649545 m
Flow above drain level (4K₁h²): 0.72 m²/day
GATE tip
Keep q in m/day when K is in m/day: 5 mm/day = 0.005 m/day.
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Evapotranspiration Calculator
ET₀ = p (0.46 T + 8.13)
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Example: A month with a mean temperature of 25 °C and p = 0.27: Reference evapotranspiration ET₀ = 5.3001 mm/day.
Frequently asked questions
What is the drainage coefficient?
The depth of water to be removed per day (mm/day), set by rainfall excess or irrigation losses; 3–10 mm/day is common.
Why the equivalent depth d?
It replaces the true depth to the barrier to account for radial flow converging on the drains.
Sources
- The International System of Units (SI), 9th edition (SI Brochure), Bureau International des Poids et Mesures .
Last reviewed: . Factors are stored exactly and computed with 50-digit decimal arithmetic. See how we verify conversion factors.
Cite this page
APA
Scientific Converters. (2026, October 15). Drain Spacing Calculator. Retrieved October 29, 2026, from https://scientificconverters.com/calculators/drain-spacing-calculator/
IEEE
Scientific Converters, "Drain Spacing Calculator," scientificconverters.com. Accessed: Oct. 29, 2026. [Online]. Available: https://scientificconverters.com/calculators/drain-spacing-calculator/