How do you measure groundwater flow?

Engineers, hydrogeologists, environmental specialists, and government agencies are interested in groundwater, given its influence on the environment, human health, and how it affects the design and construction of infrastructure such as dams, bridges, and buildings.

Groundwater flow

Understanding groundwater flow rate and trends help engineers design structures that are safe, effective, and practical. Assessing and measuring groundwater flow is essential for effective management and protection of water resources, as well as for understanding the impact of human activities on the environment.

Why measure groundwater flow?

Measuring groundwater flow can provide vital information for managing and protecting groundwater resources and for understanding the interactions between groundwater and the environment. It can indicate the following information:

• Groundwater velocity (the rate at which water moves through the subsurface) - this can be used to estimate the time it takes for water to travel from one location to another.
• Direction of flow - important for understanding the movement of contaminants and the location of recharge areas.
• Recharge rates (the amount of water that enters the groundwater system) - important for managing water resources and predicting the effects of changes in land use or climate.
• Aquifer properties (such as hydraulic conductivity and transmissivity) - these properties are important for understanding how water moves through the subsurface.
• Groundwater-surface water interactions – to estimate the amount of groundwater that discharges to streams, lakes, and wetlands and the interactions between groundwater and surface water.

How is it measured?

There are various methods engineers, hydrogeologists, and environmental specialists, deploy to measure groundwater flow.

1. Pumping tests

This involves pumping water from a well at a constant rate or decreasing rates (step down) and measuring the water level response in nearby monitoring wells.

The data collected can be used to calculate hydraulic conductivity (the ability of fluid to pass through the pores and fractured rocks) and estimate the hydraulic properties of aquifers and evaluate the performance of a well of groundwater.

2. Tracer tests

Tracers are introduced into the groundwater system and their movement is tracked over time. By analysing the concentration of the tracer at different points, the velocity and direction of groundwater flow can be determined.

3. Geophysical methods:

Methods such as electrical resistivity and seismic surveys, can be used to measure the properties of subsurface materials that control groundwater flow.

Electrical resistivity measures the ability of a material to resist the flow of electrical current. Groundwater is typically more conductive than surrounding rock and soil, so variations in electrical resistivity can be used to map the location and depths of aquifers and the flow of groundwater.

Seismic surveys use seismic waves (generated and sent through the ground using special equipment) to observe the speed at which seismic waves travel through the ground and bounce back to the surface at different speeds, depending on the properties of the soil and rock layers they encounter. The speed can infer the properties of the subsurface materials and map the location of aquifers, faults, and other subsurface features.

4. In-situ methods:

In-situ techniques, such as the heat pulse method, use temperature sensors to measure the velocity of groundwater flow.

5. Modelling:

Groundwater flow can also be simulated using computer models, which consider the physical properties of the subsurface and the flow of water through the porous media. Models should be based on site specific field data and supplemented with general parameters if needed.

Groundwater models can be designed to predict the response of the groundwater system to changes in conditions, such as changes in pumping rates, recharge rates, land use, or climate. They are used to identify potential impacts of human activities on groundwater resources, to evaluate the effectiveness of management strategies, and to guide decision-making.