Groundwater
Flow
Learning Objectives:
- Define groundwater and its significance as a vital component of the hydrological cycle.
- Understand the interactions between surface water and groundwater.
Groundwater refers to the water stored beneath the Earth's surface within the spaces of rock and sediment, occupying the saturated zone. It is a vital component of the hydrological cycle, providing a source of drinking water and serving various industrial, agricultural, and environmental purposes.
Aquifers:
Aquifers are subsurface geological formations that contain and transmit water. They can be thought of as vast underground reservoirs, and they are typically composed of porous and permeable materials like sand, gravel, or rock. These materials have interconnected void spaces that allow water to flow through them, making aquifers natural storage tanks for groundwater.
Permeability:
It refers to the ability of an aquifer, a subsurface geological formation, to transmit water. Permeability is determined by the interconnectedness and size of void spaces in the aquifer material, such as sand or gravel. A highly permeable aquifer allows water to flow easily, while a low-permeability aquifer restricts flow.
Understanding aquifer permeability is critical for several civil engineering applications:- Water Supply: Engineers evaluate permeability to design efficient wells and extraction systems that tap into aquifers for fresh water supply.
- Contaminant Transport: Knowledge of permeability is vital for assessing the movement of pollutants in groundwater, aiding in the remediation of contaminated sites.
- Foundation Design: When constructing buildings or infrastructure on or near aquifers, engineers consider permeability to prevent issues related to groundwater seepage or instability.
- Environmental Protection: Permeability data helps in maintaining ecological balance and preserving wetlands, rivers, and lakes by regulating groundwater withdrawals.
T.C. Winter, J.W. Harvey, O.L. Franke, and W.M. Alley, Public domain, via Wikimedia Commons
Shigeru23, CC BY-SA 3.0, via Wikimedia Commons
- Aquifer
- Aquitard
- Unsaturated zone
- Water table
- Confined aquifer
- Unconfined aquifer
- Deep well
- Sort well
- Artesian well
Solved Example: 9360-01
An aquifer can hold water _________ and the state of water is ______:
A. Permanently – State of flow
B. Temporarily – State of flow
C. Permanent – State of stagnancy
D. Temporary – State of stagnancy
Correct Answer: B
Solved Example: 9360-02
The quantity of water that can be withdrawn annually and also the rate at which this withdrawal could be made without adversely affecting the inventory of the aquifer is called __________:
A. Annual yield
B. Percent yield
C. Operational yield
D. Monthly yield
Correct Answer: C
Solved Example: 9360-03
Fresh water available on the earth is very little. Out of the total fresh water available, which of the following holds the maximum percentage of the total fresh water.
A. Rivers
B. Springs
C. Glaciers
D. Water falls
Correct Answer: C
Solved Example: 9360-04
Rainwater can be used to recharge the ground water. This is referred to as:
A. Water harnessing
B. Water harvesting
C. Water saving
D. Water recharging
Correct Answer: B
Wells
Learning Objectives:
- Learn about different types of groundwater wells, such as pumping wells, monitoring wells, and dewatering wells, and how they are classified.
- Familiarize yourself with the components of a groundwater well, including the casing, screen, gravel pack, and wellhead, and their functions.
Groundwater wells are structures used to access and extract groundwater from underground aquifers.
Types of Groundwater Wells- Dug Wells: Shallow wells typically excavated by hand or machine; can be prone to contamination.
- Drilled Wells: Deeper wells created using drilling equipment; less susceptible to contamination.
- Driven Wells: Wells constructed by driving a small-diameter pipe into the ground; common in areas with shallow water tables.
Shagil Kannur, CC BY-SA 3.0, via Wikimedia Commons
Solved Example: 9139-01
The soil which can store water and allow a small quantity to flow through it over a long period is called:
A. Aquifer
B. Aquitard
C. Aquifuge
D. Aquiclude
Correct Answer: B
Solved Example: 9139-02
The geologic formation which is neither porous nor permeable, and hence neither contains nor yields groundwater is termed as:
A. Aquiclude
B. Aquifer
C. Aquitard
D. Aquifuge
Correct Answer: D
Solved Example: 9139-03
A pollutant entered into a confined aquifer of 5 m thick and porosity 25%. If the seepage discharge through the aquifer is 0.25 m$^2$/ s, the travel time of pollutant for 100 m in the aquifer will be (in seconds):
A. 20
B. 400
C. 500
D. 2000
Correct Answer: C
Solved Example: 9139-04
Dupuit's assumptions are valid for:
A. Artesian aquifer
B. Confined aquifer
C. Leaky aquifer
D. Unconfined aquifer
Correct Answer: D
Solved Example: 9139-05
The discharge per unit drawdown of a well, is called:
A. Specific storage
B. Specific yield
C. Specific capacity
D. None of the above
Correct Answer: C
Solved Example: 9139-06
A deep well:
A. Is always deeper than a shallow well
B. Has more discharge than a shallow well
C. Is weaker structurally than a shallow well
D. Both (a) and (b)
Correct Answer: B
Solved Example: 9139-07
Most suitable method for drainage of fine grained soil is:
A. Well point system
B. Vacuum method
C. Electro-osmosis method
D. Deep well system
Correct Answer: C
Solved Example: 9139-08
Strainer-type tube wells are considered unsuitable for:
A. Coarse gravel
B. Fine-grained strata
C. Clean gravel
D. All of the above
Correct Answer: B
Solved Example: 9139-09
Isopiestic lines are the contours:
A. Drawn to represent water table
B. Drawn to represent piezometric heads
C. Drawn to represent piezometric surface
D. Drawn to represent points of equal rainfall
Correct Answer: C
Solved Example: 9139-10
A ground water basin consists of 1 km$^2$ area of plains. The maximum groundwater fluctuation has been observed to be 1.0 m. What is the available ground water storage if the specific yield of the basin is 10%?
A. 10,000 m$^3$
B. 100,000 m$^3$
C. 1,000,000 m$^3$
D. 10,000,000 m$^3$
Correct Answer: B
Solved Example: 9504-01
Given other circumstances constant, the relation between the level of underground water and rainfall is:
A. Simple/regular
B. Opposite
C. Proportionate
D. Inversely related
Correct Answer: A
Solved Example: 9504-02
The line joining the static water level in several wells excavated through a confined aquifer, is known as:
A. Cone of penetration
B. Piezometric surface
C. Perched water table
D. Hypsometric curve
Correct Answer: B
Drawdown
Learning Objectives:
- Recognize the factors that affect groundwater drawdown, including pumping rate, aquifer properties, well design, and regional hydrogeological conditions.
- earn about the characteristics of aquifers, including permeability, porosity, and storage coefficients, and their influence on groundwater drawdown.
Groundwater drawdown refers to the lowering of the groundwater level in an aquifer due to the extraction of water from wells, pumping stations, or other sources.
Groundwater drawdown is a common consequence of groundwater pumping, which is used for various purposes such as water supply, irrigation, and industrial processes.
Groundwater drawdown can affect ecosystems, causing harm to wetlands, streams, and vegetation that rely on groundwater.
Didiervberghe, Public domain, via Wikimedia Commons
Solved Example: 9269-01
For a well, founded in a confined aquifer, if the draw-down is doubled, the discharge 'Q' will become:
A. 0.5 Q
B. 1.5 Q
C. 2.0 Q
D. 3.0 Q
Correct Answer: C
Solved Example: 9269-02
For a well, founded in a confined aquifer, if the draw-down is doubled, the discharge 'Q' will become:
A. 0.5 Q
B. 1.5 Q
C. 2.0 Q
D. 3.0 Q
Correct Answer: C