Coefficient of Storage for Unconfined Aquifer Calculator

Formula Used:

\[ S'' = S_y + (\gamma / 1000) \times (\alpha + \eta \times \beta) \times B_s \]

Specific Yield (S_y):

(dimensionless)

Unit Weight of Fluid (γ):

N/m³

Compressibility (α):

(dimensionless)

Porosity of Soil (η):

(dimensionless)

Compressibility of Water (β):

(dimensionless)

Saturated Thickness of Aquifer (B_s):

Coefficient of Storage (S''):

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1. What is the Coefficient of Storage for Unconfined Aquifer?

The Coefficient of Storage for Unconfined Aquifer is a dimensionless measure that represents the volume of water taken into storage per unit surface area of the aquifer per unit change in the head. It is a crucial parameter in groundwater hydrology for understanding aquifer behavior.

2. How Does the Calculator Work?

The calculator uses the formula:

\[ S'' = S_y + (\gamma / 1000) \times (\alpha + \eta \times \beta) \times B_s \]

Where:

\( S'' \) — Coefficient of Storage for Unconfined Aquifer (dimensionless)
\( S_y \) — Specific Yield (dimensionless)
\( \gamma \) — Unit Weight of Fluid (N/m³)
\( \alpha \) — Compressibility (dimensionless)
\( \eta \) — Porosity of Soil (dimensionless)
\( \beta \) — Compressibility of Water (dimensionless)
\( B_s \) — Saturated Thickness of Aquifer (m)

Explanation: The formula accounts for both the specific yield component and the elastic storage component of an unconfined aquifer system.

3. Importance of Storage Coefficient Calculation

Details: Accurate calculation of the storage coefficient is essential for groundwater modeling, well yield analysis, and predicting aquifer response to pumping and recharge events.

4. Using the Calculator

Tips: Enter all parameters with appropriate units. Specific Yield, Compressibility, Porosity, and Compressibility of Water are dimensionless values. Unit Weight of Fluid should be in N/m³, and Saturated Thickness in meters.

5. Frequently Asked Questions (FAQ)

Q1: What is the typical range for Specific Yield?
A: Specific Yield typically ranges from 0.01 to 0.35, depending on the aquifer material. Coarse materials like sand and gravel have higher specific yields than fine-grained materials like clay.

Q2: Why is Unit Weight of Fluid divided by 1000?
A: The division by 1000 converts the unit weight from N/m³ to kN/m³, maintaining dimensional consistency in the calculation.

Q3: How does porosity affect the storage coefficient?
A: Higher porosity generally increases the storage capacity of an aquifer, as it indicates more void space available for water storage.

Q4: What is the difference between confined and unconfined aquifer storage coefficients?
A: Unconfined aquifers have much larger storage coefficients (typically 0.01-0.3) compared to confined aquifers (typically 0.00001-0.001) because they can drain by gravity.

Q5: When is this calculation most important?
A: This calculation is particularly important in groundwater resource assessment, well field design, and predicting drawdown in pumping tests for unconfined aquifers.