1. What is the Specific Yield Formula?

The Specific Yield formula calculates the percentage of water available for consumptive use in porous materials. It represents the difference between total porosity and specific retention.

2. How Does the Calculator Work?

The calculator uses the Specific Yield equation:

Where:

• \( \%Sy \) — Specific Yield Percentage (%)
• \( \eta_v \) — Volume Percent of Porosity (%)
• \( \%Sr \) — Specific Retention Percentage (%)

Explanation: The equation calculates the amount of water that can be drained by gravity from a saturated porous material, representing the water available for use.

3. Importance of Specific Yield Calculation

Details: Specific Yield is crucial for groundwater resource assessment, well design, and understanding aquifer characteristics. It helps determine how much water can be sustainably extracted from an aquifer.

4. Using the Calculator

Tips: Enter volume percent of porosity and specific retention percentage. Both values must be non-negative, and porosity should be greater than or equal to specific retention.

5. Frequently Asked Questions (FAQ)

Q1: What is the difference between porosity and specific yield?
A: Porosity represents total void space, while specific yield represents the drainable water fraction. Specific yield is always less than or equal to porosity.

Q2: What are typical specific yield values?
A: Values vary by material: sand (10-30%), gravel (15-30%), clay (1-10%), sandstone (5-30%).

Q3: How is specific yield measured in practice?
A: Through laboratory tests on core samples or field pumping tests that measure water yield from saturated materials.

Q4: Why is specific yield important for well design?
A: It helps determine sustainable pumping rates and well spacing to avoid over-extraction and aquifer depletion.

Q5: Can specific yield change over time?
A: Yes, due to factors like compaction, mineral deposition, or changes in water chemistry affecting pore spaces.