What is groundwater flow?

The term groundwater refers to the water which is found beneath the earth's surface. Pores present in the soil and rocks with fractures make a passage for rainwater to enter the earth's surface and deposit as groundwater. The flow nature and direction of groundwater under the earth's surface directly impacts the strength and compressibility of the soil, which reflects its ability to support structural loads.

The groundwater table is the upper surface of groundwater, and it can fluctuate with time. The soil beneath the groundwater remains saturated, which marks an entry point for the water to get stored. The volume of groundwater beneath the earth's surface changes continuously with time and due to various factors such as rainfall, absorption, human activity, and climatic conditions. The area beneath the water table is the aquifer. Aquifers are known to be the storehouse of groundwater.

The direction of groundwater flow is a major problem for carrying out construction and rehabilitation projects, and adequate measures need to be considered to prevent the groundwater from leakage and infiltration.

Groundwater flow systems

Groundwater recharge is a term that signifies the entry of surface water into the aquifer. The surface water from the earth's surface moves downwards and gets collected into the aquifer and get stored in the form of groundwater. The part of the surface water which is present above the ground, which contributes to the refill of an aquifer is termed as the recharge area.

There are three groundwater flow systems, briefly outlined below:

Local flow systems

The recharge area covered by the local flow systems is usually within ranges of kilometers, and they rapidly respond to an increase in groundwater recharge. The availability of local flow systems is limited to areas of higher relief, like foothills, hillslopes, and ranges.

Intermediate flow systems

The intermediate flow systems have a slower response to the groundwater recharge as they have a larger capacity as compared to the local flow systems. The intermediate flow systems require a longer filling time. The availability of intermediate flow systems is limited to small catchment areas, like valleys, including streamflow between individual catchments.

Regional groundwater flow systems

They are usually characterized by one-dimensional flow along the lateral direction. Regional groundwater flow systems have the highest storage capacity and have the maximum recharge time than the local flow systems and intermediate flow systems. Regional groundwater flow systems usually occur in low relief areas like the alluvial plains. The regional flow system can also be overlain by local flow and intermediate systems. The aquifers in this flow system remain either completely or partially confined into the groundwater system.

Mechanism of groundwater circulation

In hydrogeology, the main constituents of a hydrologic cycle are surface water and groundwater. The mechanism begins with the precipitation of soil. The soil soaks the surface water which is made available above the ground by snow, rainfall, and hail. The water soaking quality depends on the soil type and intensity and length of the rainfall or snow or hail. Absorption of water is faster into the soil which is primarily composed of sand. Water that cannot be absorbed into the soil called the no-flow condition, due to poor permeability, usually flows in a specific direction forming runoff streams. As the soil becomes saturated with the surface water, it slowly moves downwards receiving a suitable downgradient and recharges the groundwater storage. The water is made available into the surface of the soil through various groundwater discharge areas.

How to contaminate groundwater?

There are many possible ways groundwater can get contaminated. Harmful liquid-based chemicals and contaminants can soak into the soil contaminating the groundwater reserves. The presence of potentiometric sources of groundwater polluting sources, such as plumes is also a major source of contamination of groundwater reserves. The movement of plumes along with groundwater forms an equipotential source for large volumes of groundwater contamination. This process leads to a polluted groundwater head which is ultimately collected by the households through discharge areas.

Factors affecting groundwater contamination

There are three primary factors that govern the factors affecting groundwater contamination, they are advection, sorption, and biological degradation. These factors are explained briefly below:

Advection

The contaminants and the pollutants initially present in a certain cross-sectional area of the groundwater reserves moves with the flow of groundwater and contaminate a fresh groundwater reserve.

Sorption

In sorption, the contaminants stick to the soil particles which making harder for the surface water to recharge the groundwater reserves. This condition also makes the contaminants harder to get cleaned.

Biological degradation

In this process, the bacteria and fungi present in the soil play a major role. They often use toxic substances for food and energy resources which intern breaks down the contaminants thus allowing a passage through the soil pores to reach the groundwater reserves.

Context and Applications

The topic of groundwater flow can be found in various undergraduate degree courses like

• Bachelors in Technology (Civil Engineering)
• Bachelors in Science (Biology)
• Masters in Technology (Civil Engineering specialized in Hydrology)
• Masters in Technology (Civil Engineering specialized in Soil Engineering)

Practice Problems

1. Which of the following is known as the storehouse for groundwater?

1. Aquitard
2. Aquifer
3. Water table
4. None of these

Correct option- b

Explanation: Aquifers are known as the storehouse for groundwater. It is found beneath the water table.

2. In which of the following groundwater flow system, the flow of water is characterized by the lateral flow?

1. Regional flow systems
2. Local flow systems
3. Intermediate flow systems
4. All of these

Correct option- a

Explanation: Regional flow systems are characterized by one-dimensional flows which are in lateral directions.

3. In which of the following factors for groundwater contamination, the contaminants stick to the soil particles?

1. Advection
2. Sorption
3. Biological degradation
4. None of these

Correct option- b

Explanation: In sorption, the contaminants or the pollutants stick to the soil particles making it harder for the surface water to pass through the soil pores and recharge groundwater reserves.

4. Which of the following is true for groundwater recharge?

1. It is the availability of water at the groundwater table.
2. It is the permeability of the soil that permits the passage of surface water into the ground.
3. It signifies the entry of surface water into the aquifer.
4. It signifies groundwater discharge areas.

Correct option- c

Explanation: Groundwater recharge signifies the entry of surface water present above the soil into the aquifers.

5. Which of the following correctly resembles a plume?

1. Plumes are the pre-collection of contaminated water.
2. Plumes are water available beneath the ground that flows with groundwater.
3. Plumes are water sources present above the earth's surface which contaminates groundwater.
4. All of these

Correct option- a

Explanation: Plumes are stagnant water areas formed beneath the ground which are the major source of contamination of groundwater. The flow of plume water along with the groundwater plays a major role in the contamination of a large volume of fresh groundwater reserves.