Question

The storage coefficient of aquifer represents

• A. Ratio of specific yield to porosity
• B. Volume of water retained in storage per unit rise in head
• C. Volume of water released from storage per unit decline in head
• D. Ratio of specific retention to specific yield

Hint:

• Storage Coefficient (S) or Storativity: The volume of water an aquifer releases from or takes into storage per unit surface area of the aquifer per unit change in hydraulic head.
• It's a measure of how much water can be obtained from an aquifer by lowering the water level (head).
• For unconfined aquifers, $S \approx \text{Specific Yield (S}_y\text{)}$.
• For confined aquifers, $S = \text{Specific Storage (S}_s\text{)} \times \text{aquifer thickness (b)}$.

Answer 1

The Correct Option is C

The question asks about what the storage coefficient of an aquifer represents.

1. Understanding the Concepts:

- Storage Coefficient (S): The volume of water an aquifer releases from or takes into storage per unit surface area of the aquifer per unit change in head. It is dimensionless.
- Specific Yield (Sy): The volume of water that an unconfined aquifer releases from storage by gravity drainage per unit surface area of aquifer per unit decline in the water table.
- Porosity: The ratio of the volume of void space to the total volume of the rock or soil.
- Specific Retention: The amount of water retained in the pores of a rock or soil against the force of gravity.

2. Analyzing the Options:

- Ratio of specific yield to porosity: Incorrect, as the storage coefficient isn't a direct ratio of specific yield to porosity.
- Volume of water retained in storage per unit rise in head: While related, this defines storage coefficient relating to water going *into* storage; the question asks about a general definition.
- Volume of water released from storage per unit decline in head: This accurately describes the storage coefficient's function when water is being *released* from the aquifer.
- Ratio of specific retention to specific yield: Incorrect; storage coefficient is more related to the properties of the aquifer matrix (compressibility) and the water (compressibility and density).

3. Determining the correct answer:

The storage coefficient is defined as the volume of water an aquifer releases from storage per unit surface area of the aquifer per unit decline in the hydraulic head, or the volume of water it takes into storage per unit rise in hydraulic head.

Final Answer:

The storage coefficient of an aquifer represents Volume of water released from storage per unit decline in head.