Keyline Design Calculator

Keyline design, developed by P.A. Yeomans and first published in his 1954 book *The Keyline Plan* (substantially expanded in 1965 as *Water for Every Farm*), uses subsoil plowing on a specific off-contour pattern to slow and redirect rainwater from wet valleys toward dry ridges rather than letting it all run off along the natural drainage lines. This calculator estimates the practical logistics of that pattern: treating the field as roughly square from its acreage, it divides the field's side length by the chosen line spacing (3-5 ft for intensive management, 5-10 ft for extensive) to get the number of rip lines, then multiplies out to total linear footage and converts to ripping hours using a tractor speed that slows down as ripping depth increases (deeper ripping is harder on the equipment and soil). Fuel burn scales the same way — deeper rips draw more gallons per hour — and gets combined with a flat $30/hr labor rate for a total cost per acre.

The water benefit side models each rip line as holding a roughly triangular cross-section of storage volume based on ripping depth, then estimates a "redistribution percentage" — how much of the annual rainfall becomes more effectively usable by the field, capped at 40% — that increases with both slope (steeper land has more water to redirect from valleys to ridges) and ripping depth (deeper channels store and infiltrate more before runoff moves on). That redistribution percentage is applied against actual annual rainfall to estimate additional effective gallons per acre per year. These water-redistribution figures are drawn from Yeomans' field-observed ranges (15-35% typical), not a hydrologic simulation, so they're best used to compare scenarios against each other rather than treated as a guaranteed yield of extra water — actual gains depend heavily on soil texture, real storm intensity, and how precisely the plow follows the true keyline contour.