Question

Measurement of specific yield of an aquifer in field is done by

• A. Slug tests
• B. Grain size analysis
• C. Drain tests
• D. Pumping tests

Hint:

• Pumping tests are field procedures where a well is pumped and water level changes (drawdown) are monitored.
• Analysis of pumping test data allows for the estimation of aquifer properties like transmissivity and storativity.
• For unconfined aquifers, the storativity determined from a pumping test (especially after delayed yield effects) is taken as the specific yield.
• Slug tests are more for local hydraulic conductivity. Grain size analysis is a lab method for estimation.

Answer 1

The Correct Option is D

The question asks about how to measure the specific yield of an aquifer in the field.

1. Understanding the Concepts:

- 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.
- Slug Tests: A method for determining the hydraulic conductivity of an aquifer by introducing a known volume of water (or removing it) and measuring the water level change over time in a well.
- Grain Size Analysis: A method of determining the particle size distribution of a soil or sediment sample. Can be used to estimate porosity and, indirectly, *potential* specific yield, but it does not provide a direct measurement of specific yield in the field.
- Drain Tests: A method for determining specific yield from a small sample but not suitable for field measurement of aquifer's specific yield.
- Pumping Tests: A method for determining the hydraulic properties of an aquifer by pumping a well at a known rate and observing the drawdown in nearby observation wells. This test helps estimate transmissivity, storativity, and specific yield.

2. Analyzing the Options:

- Slug tests: Primarily used to determine hydraulic conductivity (permeability).
- Grain size analysis: Can be used to estimate porosity and, indirectly, potential specific yield, but it does not provide a direct measurement of specific yield in the field.
- Drain tests: Provides a direct measurement of specific yield from a small sample but not suitable for field measurement of aquifer's specific yield
- Pumping tests: Pumping tests combined with observation wells can be used to estimate the specific yield of unconfined aquifers by observing the water table drawdown over a larger area, making it more representative of the aquifer as a whole.

3. Determining the correct answer:

Pumping tests, particularly with observation wells, are the most reliable and common method for estimating the specific yield of an aquifer in the field.

Final Answer:

Measurement of specific yield of an aquifer in the field is done by Pumping tests.