Well Pump Drawdown & Recovery Rate Calculator

ANA›Life Services Authority›National Calculator Authority›Well Pump Drawdown & Recovery Rate Calculator

.calc-container { max-width: 640px; margin: 2rem 0; padding: 1.5rem; background: #fff; border: 1px solid #ddd; border-radius: 8px; box-shadow: 0 1px 3px rgba(0,0,0,0.06); font-family: system-ui, -apple-system, sans-serif; } .calc-container h3 { font-family: Georgia, serif; font-size: 1.15rem; color: #1a1a1a; margin-bottom: 1rem; padding-bottom: 0.5rem; border-bottom: 2px solid var(--ac, #3d5a80); } .calc-row { display: flex; align-items: center; gap: 0.75rem; margin-bottom: 0.75rem; flex-wrap: wrap; } .calc-row label { min-width: 160px; font-size: 0.9rem; color: #333; font-weight: 500; } .calc-row input[type="number"], .calc-row select { flex: 1; min-width: 120px; max-width: 200px; padding: 0.5rem 0.6rem; border: 1px solid #ccc; border-radius: 4px; font-size: 0.9rem; font-family: system-ui, sans-serif; color: #1a1a1a; background: #fafaf8; } .calc-row input:focus, .calc-row select:focus { outline: none; border-color: var(--ac, #3d5a80); box-shadow: 0 0 0 2px rgba(26,74,138,0.12); } .calc-row .unit { font-size: 0.82rem; color: #888; min-width: 30px; } .calc-btn { display: inline-block; margin-top: 0.5rem; padding: 0.55rem 1.5rem; background: var(--ac, #3d5a80); color: #fff; border: none; border-radius: 4px; font-size: 0.9rem; font-weight: 600; cursor: pointer; font-family: system-ui, sans-serif; } .calc-btn:hover { opacity: 0.9; } .calc-result { margin-top: 1.25rem; padding: 1rem 1.25rem; background: #f0f6fc; border-left: 3px solid var(--ac, #3d5a80); border-radius: 0 6px 6px 0; display: none; } .calc-result.visible { display: block; } .calc-result-label { font-size: 0.78rem; text-transform: uppercase; letter-spacing: 0.06em; color: #666; margin-bottom: 0.25rem; } .calc-result-value { font-size: 1.6rem; font-weight: 700; color: var(--ac, #3d5a80); } .calc-result-detail { font-size: 0.85rem; color: #555; margin-top: 0.5rem; line-height: 1.5; } .calc-note { margin-top: 1rem; font-size: 0.8rem; color: #888; font-style: italic; } .calc-grid { display: grid; grid-template-columns: 1fr 1fr; gap: 0.75rem; margin-top: 0.75rem; } .calc-grid-item { padding: 0.6rem 0.8rem; background: #f8f9fa; border-radius: 4px; border: 1px solid #eee; } .calc-grid-item .label { font-size: 0.75rem; color: #888; text-transform: uppercase; letter-spacing: 0.04em; } .calc-grid-item .value { font-size: 1.1rem; font-weight: 600; color: #1a1a1a; } @media (max-width: 720px) { .calc-row { flex-direction: column; align-items: flex-start; gap: 0.3rem; } .calc-row label { min-width: auto; } .calc-row input[type="number"], .calc-row select { max-width: 100%; width: 100%; } .calc-grid { grid-template-columns: 1fr; } } .calc-chart { margin: 1rem 0; text-align: center; } .calc-chart svg { max-width: 100%; height: auto; } .calc-chart-legend { display: flex; flex-wrap: wrap; justify-content: center; gap: 0.6rem 1.2rem; margin-top: 0.6rem; font-size: 0.8rem; color: #555; } .calc-chart-legend span { display: inline-flex; align-items: center; gap: 0.3rem; } .calc-chart-legend i { display: inline-block; width: 10px; height: 10px; border-radius: 2px; font-style: normal; } .calc-related { max-width: 640px; margin: 2rem 0 1rem; padding: 1.25rem 1.5rem; background: #f8f9fa; border: 1px solid #e8e8e8; border-radius: 8px; } .calc-related h3 { font-family: Georgia, serif; font-size: 1rem; color: #1a1a1a; margin: 0 0 0.75rem; padding-bottom: 0.4rem; border-bottom: 2px solid var(--ac, #3d5a80); } .calc-related-list { list-style: none; padding: 0; margin: 0 0 0.75rem; display: grid; grid-template-columns: 1fr 1fr; gap: 0.4rem 1.5rem; } .calc-related-list li a { font-size: 0.88rem; color: var(--ac, #3d5a80); text-decoration: none; } .calc-related-list li a:hover { text-decoration: underline; } .calc-browse-all { margin: 0.5rem 0 0; font-size: 0.9rem; font-weight: 600; } .calc-browse-all a { color: var(--ac, #3d5a80); text-decoration: none; } .calc-browse-all a:hover { text-decoration: underline; } @media (max-width: 720px) { .calc-related-list { grid-template-columns: 1fr; } }

Well Pump Drawdown & Recovery Rate Calculator

Calculate the drawdown in a pumping well and estimate aquifer recovery rate using the Theis equation and specific capacity method. Useful for well design, pump sizing, and aquifer characterization.

### Pumping Test Parameters

Static Water Level (ft below surface)

Pumping Water Level (ft below surface)

Pumping Rate (GPM)

Pumping Duration (minutes)

### Recovery Test Parameters

Water Level After Recovery Period (ft below surface)

Recovery Time Elapsed (minutes)

Well Casing Radius (inches)

Aquifer Saturated Thickness (ft)

Calculate Drawdown & Recovery

### Results

function welCalc() { const errEl = document.getElementById('wel-error'); const resEl = document.getElementById('wel-result'); const gridEl = document.getElementById('wel-result-grid'); errEl.style.display = 'none'; resEl.style.display = 'none'; gridEl.innerHTML = '';

// --- Read inputs --- const staticLevel = parseFloat(document.getElementById('wel-static-level').value); const pumpingLevel = parseFloat(document.getElementById('wel-pumping-level').value); const pumpRate = parseFloat(document.getElementById('wel-pump-rate').value); const pumpDuration = parseFloat(document.getElementById('wel-pump-duration').value); const recoveryLevel = parseFloat(document.getElementById('wel-recovery-level').value); const recoveryTime = parseFloat(document.getElementById('wel-recovery-time').value); const wellRadiusIn = parseFloat(document.getElementById('wel-well-radius').value); const aquiferThick = parseFloat(document.getElementById('wel-aquifer-thickness').value);

// --- Validation --- const fields = [ [staticLevel, 'Static Water Level'], [pumpingLevel, 'Pumping Water Level'], [pumpRate, 'Pumping Rate'], [pumpDuration, 'Pumping Duration'], [recoveryLevel, 'Recovery Water Level'], [recoveryTime, 'Recovery Time'], [wellRadiusIn, 'Well Casing Radius'], [aquiferThick, 'Aquifer Saturated Thickness'] ]; for (const [v, name] of fields) { if (isNaN(v) || v === '') { errEl.textContent = name + ' is required.'; errEl.style.display = 'block'; return; } if (v pumpingLevel) { errEl.textContent = 'Recovery Water Level should be between the Static and Pumping levels.'; errEl.style.display = 'block'; return; } if (wellRadiusIn > 36) { errEl.textContent = 'Well Casing Radius seems unusually large. Please verify (max 36 inches).'; errEl.style.display = 'block'; return; }

// --------------------------------------------------------------- // CORE CALCULATIONS // ---------------------------------------------------------------

// 1. Drawdown (s) — difference between pumping level and static level // s = h_static - h_pumping (both measured as depth below surface) // Since depth increases downward: s = pumpingLevel - staticLevel const drawdown = pumpingLevel - staticLevel; // ft

// 2. Residual Drawdown after recovery period // s' = recoveryLevel - staticLevel const residualDrawdown = recoveryLevel - staticLevel; // ft

// 3. Recovery amount const recoveryAmount = drawdown - residualDrawdown; // ft

// 4. Specific Capacity (SC) — pumping rate per unit drawdown // SC = Q / s [GPM/ft] const specificCapacity = pumpRate / drawdown;

// 5. Recovery Rate — rate at which water level rises per unit time // RR = recoveryAmount / recoveryTime [ft/min] const recoveryRate = recoveryAmount / recoveryTime; // ft/min

// 6. Recovery Percentage at the measured time // RP = (recoveryAmount / drawdown) * 100 const recoveryPct = (recoveryAmount / drawdown) * 100;

// 7. Transmissivity estimate (T) using Cooper-Jacob approximation // T ≈ (Q * ln(t2/t1)) / (4π * Δs) // Simplified single-point estimate from specific capacity: // T ≈ SC * 1500 (empirical, Driscoll 1986, for confined aquifer, GPM/ft → gpd/ft) // Convert: 1 GPM/ft ≈ 1440 gpd/ft; T(ft²/day) ≈ SC(GPM/ft) * 1440 / 7.48 // More rigorous: T(ft²/day) = SC(GPM/ft) * 192.5 (Theis, 1963 approximation) const transmissivity = specificCapacity * 192.5; // ft²/day

// 8. Hydraulic Conductivity (K) = T / b where b = aquifer saturated thickness const hydraulicConductivity = transmissivity / aquiferThick; // ft/day

// 9. Well Yield Sustainability check // Casing storage volume per foot = π * r² (ft³/ft) // r in feet const wellRadiusFt = wellRadiusIn / 12; const casingStoragePerFt = Math.PI * wellRadiusFt * wellRadiusFt; // ft³/ft // Volume pumped during test (gallons → ft³; 1 gal = 0.13368 ft³) const volumePumped = pumpRate * pumpDuration * 0.13368; // ft³ // Drawdown from casing storage alone (if aquifer contributed nothing) const casingOnlyDrawdown = volumePumped / casingStoragePerFt; // ft

// 10. Estimated time to full recovery (linear extrapolation) // Assumes recovery rate is approximately constant (conservative) let fullRecoveryTime = null; if (recoveryRate > 0) { fullRecoveryTime = residualDrawdown / recoveryRate; // minutes }

// 11. Aquifer contribution vs casing storage // If casingOnlyDrawdown >> actual drawdown → aquifer is contributing const aquiferContribPct = Math.min(100, Math.max(0, (1 - (drawdown / casingOnlyDrawdown)) * 100));

// --------------------------------------------------------------- // DISPLAY RESULTS // --------------------------------------------------------------- function row(label, value, unit, note) { return '' + '' + label + (note ? ' (' + note + ')' : '') + '' + '' + value + ' ' + unit + '' + ''; }

let html = ''; html += row('Drawdown (s)', drawdown.toFixed(2), 'ft', 'at end of pumping'); html += row('Residual Drawdown (s')', residualDrawdown.toFixed(2), 'ft', 'after ' + recoveryTime + ' min recovery'); html += row('Recovery Amount', recoveryAmount.toFixed(2), 'ft'); html += row('Recovery Rate', recoveryRate.toFixed(4), 'ft/min'); html += row('Recovery Rate', (recoveryRate * 12).toFixed(3), 'in/min'); html += row('Recovery Percentage', recoveryPct.toFixed(1), '%', 'at ' + recoveryTime + ' min'); html += row('Specific Capacity', specificCapacity.toFixed(3), 'GPM/ft'); html += row('Transmissivity (T)', transmissivity.toFixed(1), 'ft²/day', 'Theis approx.'); html += row('Hydraulic Conductivity (K)', hydraulicConductivity.toFixed(4), 'ft/day');

if (fullRecoveryTime !== null) { if (fullRecoveryTime = 80) { interp = '✅ Good Recovery — Well and aquifer appear to be performing well.'; interpClass = 'calc-interp-good'; } else if (recoveryPct >= 50) { interp = '⚠️ Moderate Recovery — Monitor well performance; aquifer may have limited recharge.'; interpClass = 'calc-interp-warn'; } else { interp = '🔴 Poor Recovery — Consider reducing pump rate or investigating aquifer limitations.'; interpClass = 'calc-interp-bad'; } html += '' + interp + '';

gridEl.innerHTML = html; resEl.style.display = 'block'; }

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#### Formulas Used

Drawdown: s = Hpumping − Hstatic (ft)

Residual Drawdown: s' = Hrecovery − Hstatic (ft)

Recovery Rate: RR = (s − s') / trecovery (ft/min)

Recovery Percentage: RP = [(s − s') / s] × 100 (%)

Specific Capacity: SC = Q / s (GPM/ft)

Transmissivity (Theis, 1963 approximation): T ≈ SC × 192.5 (ft²/day)

Hydraulic Conductivity: K = T / b (ft/day), where b = saturated aquifer thickness

Casing Storage Volume: Vcasing = π × r² × Δh (ft³)

#### Assumptions & References

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References

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