Well Efficiency Calculator
The Well Efficiency Calculator is a practical online tool designed to help hydrogeologists, well owners, water engineers, and farmers quickly estimate well efficiency (%) based on established groundwater hydrology principles. Well efficiency is a key performance indicator in well testing, showing what percentage of observed drawdown is due to natural aquifer losses versus additional well losses (turbulent flow, screen clogging, etc.). A good well typically has efficiency >70–80%.
About the Well Efficiency Calculator
Well Efficiency Calculator helps determine how effectively your water well performs by comparing theoretical aquifer drawdown (laminar flow losses in the formation) to actual measured drawdown in the pumping well. This tool follows peer-reviewed scientific methodologies from hydrogeology, primarily based on step-drawdown tests and equations developed by Jacob (1947), extended by Rorabaugh (1953), and described in standard references like Groundwater and Wells (Driscoll, 1986) and Kruseman & de Ridder (1994).
Well efficiency (%) is calculated as:
Efficiency (%) = (Aquifer Loss Drawdown / Total Measured Drawdown) × 100
Aquifer loss (theoretical laminar drawdown) is typically B × Q, where B is the linear aquifer-loss coefficient (derived from Cooper-Jacob straight-line method or Theis curve matching in a step-drawdown test), and Q is the pumping rate. Total drawdown includes both aquifer loss + well loss (turbulent/entrance/screen losses, often C × Q² or C × Q^p).
Importance of Well Efficiency Testing
Monitoring well efficiency is critical for sustainable groundwater extraction. Low efficiency (<60–65%) indicates excessive well losses from partial plugging, poor screen design, turbulent flow near the well bore, or biofouling/mineral scaling. This increases energy costs for pumping, reduces well yield, shortens pump life, and may lead to well rehabilitation or replacement. High efficiency ensures cost-effective operation, better aquifer management, and compliance with water resource regulations.
In agricultural, municipal, and industrial settings, regular efficiency checks help predict long-term well performance, optimize pump selection, and prevent over-pumping that could cause land subsidence or saltwater intrusion.
User Guidelines & How to Use the Calculator
- Obtain data from a step-drawdown test or constant-rate pumping test.
- Enter the total measured drawdown (s_w) in the pumping well after stabilization (usually the final step or design rate).
- Enter the theoretical aquifer loss drawdown (often B × Q from test analysis using Cooper-Jacob or Theis method).
- If you have transmissivity (T), time (t), well radius (r_w), and storativity (S), you can approximate theoretical drawdown using the Cooper-Jacob equation: s = (Q / (4πT)) × ln(2.25Tt / r_w²S).
- Select appropriate units and click Calculate.
- Results >80% indicate excellent performance; 70–80% is acceptable; <65% suggests rehabilitation may be needed.
When and Why You Should Use This Tool
Use the Well Efficiency Calculator after well construction, rehabilitation, or during routine maintenance. It's especially valuable:
- After step-drawdown tests to quantify well losses
- When comparing well performance over time (efficiency often declines with age)
- To decide whether chemical/acid treatment, surging, or screen replacement is economically justified
- In designing new wells or pump stations to ensure long-term sustainability
Purpose: Provide accurate, science-based insights to maximize well lifespan, reduce operational costs, and support responsible groundwater stewardship.
Detailed Explanation of Well Efficiency in Hydrogeology
Well efficiency is a fundamental metric in groundwater hydrology and well hydraulics. It quantifies how much of the total drawdown in a pumping well results from natural aquifer resistance (laminar flow through the porous medium) versus extra losses inside/near the well (turbulent flow, screen entrance losses, gravel pack friction, etc.).
The concept originates from early groundwater research and was formalized in equations like Jacob's (1947): s_w = BQ + CQ², where s_w is total drawdown, BQ is aquifer loss (linear), and CQ² is well loss (nonlinear/turbulent). Efficiency is then (BQ / s_w) × 100. Rorabaugh (1953) generalized it to s_w = BQ + C Q^p where p ≈ 2–2.5 in most cases.
In practice, step-drawdown tests (multiple increasing pumping rates) allow plotting specific drawdown (s/Q) vs. Q to separate linear (aquifer) and nonlinear (well) components. Software like AQTESOLV or manual curve matching with Theis/Cooper-Jacob methods estimates B and C. For confined aquifers, theoretical drawdown can also be calculated using the Theis non-equilibrium equation or its straight-line approximation (Cooper-Jacob) for late-time data: s = (Q/(4πT)) ln(2.25 T t / (r_w² S)).
Well efficiency decreases with higher pumping rates due to increasing turbulent losses. Values >70% are generally good; <50–60% often indicates serious issues requiring intervention. Factors affecting efficiency include screen slot size, gravel pack quality, development thoroughness, biofouling, incrustation, and aquifer properties like transmissivity and grain size.
Regular monitoring using tools like this Well Efficiency Calculator supports proactive well management. For more technical background, refer to the Wikipedia article on Well Efficiency Calculator concepts and well testing methods. This tool is proudly hosted with support from Agri Care Hub, your resource for agriculture and water management solutions.
Continued proper use of this calculator promotes sustainable water use, reduces energy consumption in pumping, and helps protect aquifers for future generations. Always consult a qualified hydrogeologist for complex sites or when planning major well interventions.
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