All questions of Well Hydraulics for Civil Engineering (CE) Exam

Understanding Storage Coefficient
The storage coefficient is a vital concept in groundwater hydrology, particularly in the context of aquifer properties and water movement.
Definition of Storage Coefficient
- The storage coefficient (S) is defined as the volume of water that a unit area of an aquifer releases or takes in from storage due to a unit change in hydraulic head.
Importance of Normal Component
- In this context, the unit change in the component of the head is measured in the normal direction to the surface for several reasons:
- Hydraulic Gradient: The normal component represents the vertical change in head, which directly influences the flow direction and rate within the aquifer.
- Fluid Mechanics: According to Darcy's law, groundwater movement is primarily influenced by the hydraulic gradient, which is perpendicular (normal) to the surface.
- Pressure Changes: Changes in head typically result from variations in pressure in the aquifer, which are also measured in the normal direction.
Implications of Using Normal Measurement
- Accurate Flow Representation: Measuring the head change in the normal direction allows for a more accurate representation of how groundwater flows through porous media.
- Simplified Calculations: Using the normal component simplifies calculations when determining aquifer performance and storage capacity.
Conclusion
In summary, the storage coefficient focuses on the normal component of the head change due to its direct relevance to groundwater flow and pressure dynamics in aquifers, making option 'A' the correct answer.

Understanding Coefficient of Transmissibility
The coefficient of transmissibility (T) is a crucial term in groundwater hydrology and civil engineering. It is essential to clarify its definition to understand why the statement is deemed false.
Definition of Coefficient of Transmissibility
- Rate of Flow: T represents the ability of an aquifer to transmit water.
- Unit Width: The flow is assessed through a vertical section of the aquifer with a unit width (1 meter).
- Full Saturation Height: The entire height of the aquifer is considered, not just a portion.
- Hydraulic Gradient: It is specifically measured under a unit hydraulic gradient, which is typically defined as a change in hydraulic head per unit distance.
Why the Statement is False
The statement provided is incorrect because:
- Horizontal Strip Misrepresentation: The coefficient of transmissibility is not specifically defined for a horizontal strip; rather, it applies to a vertical column of the aquifer.
- Context of Flow: The definition implies a three-dimensional flow scenario rather than being limited to a single horizontal strip.
Conclusion
In conclusion, the coefficient of transmissibility is a measure of an aquifer's capacity to transmit water, taking into account the vertical aspects of flow rather than just a horizontal strip. Hence, the correct answer to the statement is option 'B' (False). Understanding these nuances is vital for effective groundwater management and civil engineering practices.

Drawdown in Pumping Out Test

In a pumping out test, the drawdowns are observed at a number of wells. This test is conducted to determine the yield and efficiency of a well or a group of wells. The following are the details of the pumping out test:

Procedure:

1. A well is pumped at a constant rate, and the water level is measured at a number of observation wells located at different distances from the pumping well.

2. The water level in each observation well is measured several times during the test, and the drawdown corresponding to each measurement is recorded.

3. The test is continued until the water level in the pumping well stabilizes, and the drawdown at the observation wells reaches a constant value.

4. The data obtained from the test is used to plot a drawdown-time curve, which is used to determine the yield and efficiency of the well.

Interpretation:

The drawdown-time curve obtained from the pumping out test provides information about the hydraulic properties of the aquifer. The following are the interpretations that can be made from the curve:

1. The yield of the well can be determined from the maximum drawdown observed during the test.

2. The efficiency of the well can be determined from the slope of the curve during the early part of the test.

3. The hydraulic conductivity of the aquifer can be determined from the shape of the curve and the distance between the pumping well and the observation wells.

Conclusion:

The pumping out test is an important tool for determining the yield and efficiency of a well or a group of wells. The drawdowns observed at the observation wells provide valuable information about the hydraulic properties of the aquifer, which can be used to optimize the design and operation of the wells.

Explanation:

Specific yield (Sγ)
- Specific yield (Sγ) is defined as the ratio of the volume of water that a saturated soil can yield by gravity to its own volume.
- It is expressed as a percentage.

Formula for Specific Yield:
- Sγ = (Vwy / V) * 100
- where:
- Vwy = volume of water drained under gravity
- V = total volume of the soil sample

Explanation of the Formula:
- The specific yield is calculated by dividing the volume of water drained under gravity (Vwy) by the total volume of the soil sample (V).
- The result is then multiplied by 100 to express it as a percentage.

Reason for Choosing Option 'C':
- Option 'C' correctly represents the formula for specific yield by dividing Vwy by V and then multiplying the result by 100.
- This calculation is essential to determine the specific yield of a soil sample accurately.