Specific Capacity Under Unsteady Drawdown Conditions Calculator

Specific Capacity Formula:

\[ Specific\ Capacity = \frac{1}{\left(\frac{1}{4\pi T}\right)\ln\left(\frac{2.25Tt}{R_w^2 S}\right) + C_2 Q_f} \]

Transmissivity (T):

m²/s

Time from start of pump (t):

seconds

Radius of the Pumping Well (Rw):

meters

Storage Coefficient (S):

Well Constant C2:

Flow Discharge (Qf):

m³/s

Specific Capacity:

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1. What is Specific Capacity Under Unsteady Drawdown Conditions?

Specific Capacity under unsteady drawdown conditions refers to the yield of a well per unit drawdown, accounting for time-dependent changes in the aquifer system. It provides a measure of well efficiency and aquifer productivity during pumping tests.

2. How Does the Calculator Work?

The calculator uses the Specific Capacity formula:

\[ Specific\ Capacity = \frac{1}{\left(\frac{1}{4\pi T}\right)\ln\left(\frac{2.25Tt}{R_w^2 S}\right) + C_2 Q_f} \]

Where:

\( T \) — Transmissivity (m²/s)
\( t \) — Time from start of pump (seconds)
\( R_w \) — Radius of the Pumping Well (meters)
\( S \) — Storage Coefficient
\( C_2 \) — Well Constant
\( Q_f \) — Flow Discharge (m³/s)
\( \pi \) — Pi constant (approximately 3.1416)
\( \ln \) — Natural logarithm function

Explanation: The equation accounts for aquifer properties, well characteristics, and pumping conditions to determine the specific capacity under unsteady state conditions.

3. Importance of Specific Capacity Calculation

Details: Accurate specific capacity calculation is crucial for well design, aquifer characterization, pumping test analysis, and determining sustainable yield of water wells.

4. Using the Calculator

Tips: Enter all required parameters with appropriate units. Ensure values are positive and within reasonable ranges for accurate results.

5. Frequently Asked Questions (FAQ)

Q1: What is the difference between steady-state and unsteady-state specific capacity?
A: Steady-state specific capacity assumes constant drawdown over time, while unsteady-state accounts for time-dependent changes in the aquifer system during pumping.

Q2: How does well constant C2 affect specific capacity?
A: Well constant C2 represents well losses due to turbulent flow. Higher C2 values result in lower specific capacity, indicating less efficient well performance.

Q3: What are typical ranges for specific capacity values?
A: Specific capacity varies widely depending on aquifer type, but typically ranges from 0.1 to 10 m³/s/m for productive aquifers.

Q4: How does storage coefficient affect specific capacity?
A: Higher storage coefficients generally result in higher specific capacity values, as the aquifer can release more water per unit decline in head.

Q5: When is this unsteady-state formula most appropriate?
A: This formula is most appropriate for short-term pumping tests and early-time drawdown analysis before steady-state conditions are established.