Infiltration Depth & Deep Percolation Calculator

Given a layered soil profile and an applied depth of water, finds how deep the wetting front penetrates — and, given a root zone depth, how much of that water passed below the roots as deep percolation (wasted water, and a pathway for leaching chemicals out of the root zone).

Soil Profile

List layers from the surface down. Each layer needs a field capacity (θ_fc) and current water content (θ_v) — the difference is how much water that layer can still absorb per unit depth before the wetting front moves on. The last layer can be marked "extends indefinitely" if you don't know (or don't need) its bottom boundary.

Depth unit (used throughout)

Thickness

θ_fc (%)

θ_v (%)

Applied Water & Root Zone

Total infiltrated depth applied

Root zone depth (optional — leave blank to skip deep percolation)

Match textbook rounding (rounds each intermediate step to 1 decimal, like the worked example)

About this calculator

As water infiltrates, each soil layer fills to field capacity before the wetting front advances into the next layer. The depth of water a layer can still absorb is its water deficit per unit depth (θ_fc − θ_v) times its thickness — the same soil water deficit (SWD) calculation as the scheduling calculator, applied layer by layer:

SWD_layer = (θ_fc − θ_v) × thickness

The applied water fills each layer's deficit in turn; wherever it runs out mid-layer, that's the wetting front. If the front goes deeper than the root zone, the water that filled soil below the roots is lost to deep percolation — it can't be used by the crop, and it's how nitrate and other mobile chemicals leach out of the root zone.

This calculator carries full precision through every step by default. The textbook's worked example rounds each layer's SWD to 1 decimal place before moving to the next step, which compounds noticeably here (a partial-layer depth divided by a small deficit amplifies small rounding differences). Full precision gives a wetting front of about 47.7 in and deep percolation of about 0.70 in for Example 2.4/2.5, versus the textbook's rounded 46.7 in and 0.6 in — check "Match textbook rounding" above to reproduce the book's numbers exactly.

Textbook Examples 2.4 & 2.5: 4 in of water infiltrates a profile of 0–12 in (θ_fc=0.34, θ_v=0.20), 12–30 in (θ_fc=0.40, θ_v=0.33), and 30+ in (θ_fc=0.30, θ_v=0.24, unbounded). With a 36-in root zone, deep percolation ≈ 0.6–0.7 in. Click "Load textbook Example 2.4 & 2.5" above to see it worked through.