Formula Used:
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The change in drawdown formula calculates the difference in water table elevation between two observation wells in an unconfined aquifer. It's derived from the Theis equation and is used to determine aquifer properties and groundwater flow characteristics.
The calculator uses the formula:
Where:
Explanation: The formula calculates the difference in water table elevation between two observation wells based on pumping rate, well distances, and aquifer transmissivity.
Details: Accurate drawdown calculation is crucial for groundwater resource management, well design, aquifer testing, and predicting the impact of pumping on surrounding water levels.
Tips: Enter discharge in m³/s, radial distances in meters, and transmissivity in m²/s. All values must be positive numbers with r₂ > r₁ for meaningful results.
Q1: What is the difference between drawdown and change in drawdown?
A: Drawdown refers to the lowering of water level at a single point, while change in drawdown refers to the difference in drawdown between two observation points.
Q2: Why is the natural logarithm used in this formula?
A: The natural logarithm accounts for the radial flow pattern and decreasing hydraulic gradient with distance from the pumping well.
Q3: What are typical transmissivity values for aquifers?
A: Transmissivity values range from 0.1 m²/day for tight formations to over 1000 m²/day for highly productive aquifers.
Q4: When is this formula most applicable?
A: This formula is most applicable for steady-state conditions in homogeneous, isotropic unconfined aquifers with fully penetrating wells.
Q5: What are the limitations of this approach?
A: Limitations include assumptions of homogeneous aquifer properties, constant pumping rate, and negligible boundary effects.