Unconfined Aquifer Discharge Given Aquifer Constant Calculator

Formula Used:

\[ Discharge = \frac{Aquifer\ Constant}{\frac{\log\left(\frac{Radial\ Distance\ at\ Observation\ Well\ 2}{Radial\ Distance\ at\ Observation\ Well\ 1}, e\right)}{2.72 \times (Modified\ Drawdown\ 1 - Modified\ Drawdown\ 2)}} \] \[ Q = \frac{T}{\frac{\log\left(\frac{r2}{r1}, e\right)}{2.72 \times (s1' - s2')}} \]

Aquifer Constant (T):

m²/day

Radial Distance at Observation Well 1 (r1):

Radial Distance at Observation Well 2 (r2):

Modified Drawdown 1 (s1'):

Modified Drawdown 2 (s2'):

Discharge (Q):

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1. What is the Unconfined Aquifer Discharge Formula?

The formula calculates discharge from an unconfined aquifer using the aquifer constant, radial distances at observation wells, and modified drawdown values. It provides an accurate assessment of groundwater flow rates in unconfined aquifer systems.

2. How Does the Calculator Work?

The calculator uses the formula:

\[ Q = \frac{T}{\frac{\log\left(\frac{r2}{r1}, e\right)}{2.72 \times (s1' - s2')}} \]

Where:

\( Q \) — Discharge (m³/day)
\( T \) — Aquifer Constant/Transmissivity (m²/day)
\( r1 \) — Radial Distance at Observation Well 1 (m)
\( r2 \) — Radial Distance at Observation Well 2 (m)
\( s1' \) — Modified Drawdown 1 (m)
\( s2' \) — Modified Drawdown 2 (m)
\( e \) — Napier's constant (2.71828)

Explanation: The formula accounts for the logarithmic relationship between radial distances and the difference in modified drawdowns to calculate aquifer discharge.

3. Importance of Discharge Calculation

Details: Accurate discharge calculation is crucial for groundwater resource management, well field design, and understanding aquifer behavior under pumping conditions.

4. Using the Calculator

Tips: Enter all values in appropriate units. Aquifer constant and radial distances must be positive values. Drawdown values should be non-negative with s1' > s2' for meaningful results.

5. Frequently Asked Questions (FAQ)

Q1: What is an unconfined aquifer?
A: An unconfined aquifer has a water table that serves as its upper boundary and is in direct contact with the atmosphere.

Q2: What does the aquifer constant represent?
A: The aquifer constant (T) represents transmissivity, which is the rate at which water flows through a unit width of aquifer under a unit hydraulic gradient.

Q3: Why use modified drawdown instead of actual drawdown?
A: Modified drawdown accounts for aquifer characteristics and provides more accurate results in unconfined aquifer calculations.

Q4: What are typical values for aquifer transmissivity?
A: Transmissivity values range from 1-1000 m²/day for most aquifers, with higher values indicating more productive aquifers.

Q5: When is this formula most applicable?
A: This formula is most applicable for steady-state flow conditions in homogeneous, isotropic unconfined aquifers with fully penetrating wells.