Aquifer Test Calculator
The Aquifer Test Calculator is an essential online tool for hydrogeologists, environmental engineers, water resource managers, and students to analyze constant-rate pumping tests in confined aquifers. Using the reliable Cooper-Jacob straight-line method, this Aquifer Test Calculator estimates key hydraulic parameters: transmissivity (T) and storativity (S), providing quick and credible insights into aquifer performance.
Aquifer tests, also known as pumping tests, are fundamental in groundwater studies for characterizing subsurface flow and storage properties.
Calculator Inputs (Cooper-Jacob Method)
About the Aquifer Test Calculator
The Aquifer Test Calculator employs the Cooper-Jacob (1946) straight-line method, a widely accepted simplification of the Theis (1935) nonequilibrium solution for transient flow in confined aquifers. This method is based on peer-reviewed hydrogeological principles and is commonly used worldwide for interpreting constant-rate pumping tests.
Aquifer tests involve pumping water at a constant rate from a well while measuring drawdown in observation wells (or the pumping well for approximate analysis). The response reveals aquifer transmissivity (ability to transmit water) and storativity (ability to store and release water).
Scientific Basis and Formulas
The Cooper-Jacob method approximates the Theis equation for small u (late times or small distances):
$$ s = \frac{Q}{4\pi T} \left( -0.5772 - \ln u \right) = \frac{Q}{4\pi T} \ln \left( \frac{2.25 T t}{r^2 S} \right) $$
Plotting drawdown (s) vs. log(t) yields a straight line with slope:
$$ \Delta s = \frac{2.3 Q}{4\pi T} $$
Thus, transmissivity:
$$ T = \frac{2.3 Q}{4\pi \Delta s} $$
And storativity from the time intercept t₀ (where s=0 on the extrapolated line):
$$ S = \frac{2.25 T t_0}{r^2} $$
These formulas are derived from the Theis well function approximation and are accurate when u < 0.05, typically after early-time effects dissipate.
Importance of Aquifer Tests
Accurate aquifer characterization is crucial for sustainable groundwater management, well design, contamination assessment, and water supply planning. Overexploitation without understanding transmissivity and storativity can lead to excessive drawdown, land subsidence, saltwater intrusion, or ecosystem damage. Aquifer tests provide direct field evidence of hydraulic properties, far superior to laboratory estimates.
Regulatory bodies like the EPA and WHO recommend pumping tests for major groundwater developments to ensure long-term viability.
When and Why You Should Use This Tool
Use the Aquifer Test Calculator for:
- Analyzing constant-rate pumping test data in confined aquifers
- Quick estimation of T and S during field work or preliminary studies
- Educational purposes to understand transient groundwater flow
- Screening-level assessments before advanced numerical modeling
- Verification against more complex methods like full Theis curve matching
It is ideal when semi-log plots show straight-line behavior in late-time drawdown data.
User Guidelines
- Prepare a semi-log plot of drawdown vs. time (log scale on time axis).
- Fit a straight line to late-time data (ignoring early curvature).
- Measure Δs as drawdown change over one log cycle of time.
- Find t₀ where the line intersects zero drawdown.
- Input values with consistent units (e.g., Q in m³/day, lengths in m).
- Verify u < 0.05 for applicability (late-time data).
Purpose of the Aquifer Test Calculator
This tool aims to make reliable hydrogeological analysis accessible to professionals and learners worldwide. By implementing verified formulas in a user-friendly interface, it promotes best practices in groundwater evaluation and supports informed resource management.
Typical parameter ranges for confined aquifers:
| Parameter | Typical Range | Notes |
|---|---|---|
| Transmissivity (T) | 10⁻⁵ – 10⁻¹ m²/s (1 – 10,000 m²/day) | Higher in karst or gravel |
| Storativity (S) | 10⁻⁵ – 10⁻³ | Low due to confined conditions |
| Pumping Rate (Q) | 100 – 5000 m³/day | Site-dependent |
| Distance (r) | 10 – 500 m | Multiple wells preferred |
In conclusion, the Aquifer Test Calculator facilitates evidence-based groundwater science, essential for addressing global water challenges. For detailed definitions and methods, refer to the Aquifer Test Calculator page on Wikipedia or explore resources at Agri Care Hub.
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