Soil Infiltration Rate Calculator

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Soil Infiltration Rate Calculator

Calculate cumulative infiltration and infiltration rate using Philip's Two-Term Method or the Green-Ampt Method for various soil types.

Calculation Method

Philip's Two-Term Method Green-Ampt Method

Sorptivity, S (mm/hr^0.5)

Soil water absorption capacity (typical range: 5–100 mm/hr⁰·⁵)

Transmissivity Constant, A (mm/hr)

Steady-state transmission rate (typical range: 1–50 mm/hr)

Time, t (hours)

Elapsed time since infiltration began (must be > 0)

Soil Texture Class

Sand Loamy Sand Sandy Loam Loam Silt Loam Sandy Clay Loam Clay Loam Silty Clay Loam Sandy Clay Silty Clay Clay

Saturated Hydraulic Conductivity, K_s (mm/hr)

Auto-filled from soil type; can be overridden

Wetting Front Suction Head, ψ (mm)

Capillary suction at wetting front; auto-filled from soil type

Effective Porosity, θ_e (dimensionless)

Fraction of soil volume available for water (0–1); auto-filled

Initial Soil Moisture Content, θ_i (dimensionless)

Volumetric water content before rainfall (must be

Time, t (hours)

Elapsed time since infiltration began (must be > 0)

Calculate Results will appear here.

// Green-Ampt soil parameters: [Ks (mm/hr), psi (mm), theta_e] // Source: Rawls, Brakensiek & Miller (1983); Chow, Maidment & Mays (1988) const soiSoilParams = { sand: [117.8, 49.5, 0.417], loamy_sand: [ 29.9, 61.3, 0.401], sandy_loam: [ 10.9, 110.1, 0.412], loam: [ 3.4, 88.9, 0.434], silt_loam: [ 6.5, 166.8, 0.486], sandy_clay_loam: [ 1.5, 218.5, 0.330], clay_loam: [ 1.0, 208.8, 0.390], silty_clay_loam: [ 1.0, 273.0, 0.432], sandy_clay: [ 0.6, 239.0, 0.321], silty_clay: [ 0.5, 292.2, 0.423], clay: [ 0.3, 316.3, 0.385] };

function soiToggleMethod() { const method = document.getElementById('soi-method').value; document.getElementById('soi-philip-inputs').style.display = (method === 'philip') ? '' : 'none'; document.getElementById('soi-greenampt-inputs').style.display = (method === 'greenampt') ? '' : 'none'; document.getElementById('soi-result').innerHTML = 'Results will appear here.'; }

function soiLoadSoilParams() { const type = document.getElementById('soi-soil-type').value; const p = soiSoilParams[type]; document.getElementById('soi-hydraulic-cond').value = p[0]; document.getElementById('soi-suction').value = p[1]; document.getElementById('soi-porosity').value = p[2]; }

// Load defaults on page load soiLoadSoilParams();

function soiCalc() { const method = document.getElementById('soi-method').value; const resultDiv = document.getElementById('soi-result');

if (method === 'philip') { const S = parseFloat(document.getElementById('soi-sorptivity').value); const A = parseFloat(document.getElementById('soi-transmissivity').value); const t = parseFloat(document.getElementById('soi-time-philip').value);

if (isNaN(S) || isNaN(A) || isNaN(t)) { resultDiv.innerHTML = '⚠ Please fill in all fields.'; return; } if (S ⚠ Sorptivity and Transmissivity must be ≥ 0.'; return; } if (t ⚠ Time must be greater than 0.'; return; }

// Philip's Two-Term Method // Cumulative infiltration: F(t) = S·t^0.5 + A·t [mm] // Infiltration rate: f(t) = 0.5·S·t^(-0.5) + A [mm/hr] const F = S * Math.pow(t, 0.5) + A * t; const f = 0.5 * S * Math.pow(t, -0.5) + A;

// Steady-state rate (as t → ∞, f → A) const f_steady = A;

resultDiv.innerHTML = ` ### Philip's Two-Term Method Results

ParameterValue Cumulative Infiltration, F(t)${F.toFixed(3)} mm Infiltration Rate, f(t)${f.toFixed(4)} mm/hr Steady-State Rate (t→∞)${f_steady.toFixed(4)} mm/hr Sorptivity, S${S.toFixed(3)} mm/hr⁰·⁵ Transmissivity Constant, A${A.toFixed(3)} mm/hr Time, t${t.toFixed(3)} hr `;

} else { // Green-Ampt Method const Ks = parseFloat(document.getElementById('soi-hydraulic-cond').value); const psi = parseFloat(document.getElementById('soi-suction').value); const te = parseFloat(document.getElementById('soi-porosity').value); const ti = parseFloat(document.getElementById('soi-initial-moisture').value); const t = parseFloat(document.getElementById('soi-time-ga').value);

if (isNaN(Ks) || isNaN(psi) || isNaN(te) || isNaN(ti) || isNaN(t)) { resultDiv.innerHTML = '⚠ Please fill in all fields.'; return; } if (Ks ⚠ Hydraulic conductivity must be > 0.'; return; } if (psi ⚠ Suction head must be ≥ 0.'; return; } if (te = 1) { resultDiv.innerHTML = '⚠ Effective porosity must be between 0 and 1.'; return; } if (ti = te) { resultDiv.innerHTML = '⚠ Initial moisture must be ≥ 0 and less than effective porosity.'; return; } if (t ⚠ Time must be greater than 0.'; return; }

// Moisture deficit (IMD = Initial Moisture Deficit) const IMD = te - ti;

// Green-Ampt cumulative infiltration (implicit equation solved iteratively): // F(t) = Ks·t + ψ·IMD·ln(1 + F(t)/(ψ·IMD)) // Solve using Newton-Raphson iteration const psiIMD = psi * IMD; let F = Ks * t; // initial guess const maxIter = 200; const tol = 1e-9;

for (let i = 0; i ParameterValue Cumulative Infiltration, F(t)${F.toFixed(3)} mm Infiltration Rate, f(t)${f.toFixed(4)} mm/hr Steady-State Rate (= K_s)${f_steady.toFixed(4)} mm/hr Initial Moisture Deficit (IMD)${IMD.toFixed(4)} ψ × IMD${psiIMD.toFixed(3)} mm Saturated Hydraulic Conductivity, K_s${Ks.toFixed(3)} mm/hr Wetting Front Suction, ψ${psi.toFixed(1)} mm Effective Porosity, θ_e${te.toFixed(3)} Initial Moisture, θ_i${ti.toFixed(3)} Time, t${t.toFixed(3)} hr `; } }

#### Formulas

Philip's Two-Term Method:

Where S = sorptivity (mm/hr⁰·⁵), A = transmissivity constant (mm/hr), t = time (hr).

Green-Ampt Method:

Where Ks = saturated hydraulic conductivity (mm/hr), ψ = wetting front suction head (mm), θe = effective porosity, θi = initial moisture content. The implicit equation is solved via Newton-Raphson iteration.

#### Assumptions & References

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References

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