What Is the Difference Between a Water Table and a Perched Water Table?

A water table refers to the pores and fractures within the ground that can become saturated with water. This area is also sometimes called the zone of saturation. A simple explanation would be the depth below where the ground is saturated. Understanding water tables, the different types of water tables, and how they behave is important for many different reasons.

Civil engineers use this information to help clients make good choices when planning construction projects. Let’s take a look at one type of water table, the perched water table.

Understanding Water Tables

Groundwater collects from different sources. It can collect from rain and other forms of precipitation or from the groundwater that is flowing into an aquifer. When enough precipitation is present in an area, this water will flow through all of the pore spaces in the soil. Eventually, a zone of saturation will be reached.

Beneath this zone, however, there are layers of permeable rock. This zone is called the phreatic zone. This is where aquifers can be found.

Water Tables and the Seasons

Water tables can change according to the seasons. With different seasonal changes, precipitation levels can change drastically. In areas where there has been little development, and the soil is relatively unaltered, the soil is generally more permeable. This makes it possible for the water table to naturally slope toward rivers. This natural sloping and drainage help to relieve pressure in the aquifers.

The occurrence of springs, rivers, lakes, and oases actually occurs when the water table comes to the surface.

What Is Perched Water Table?

A perched water table, also sometimes called a perched aquifer, occurs above the regional water table. This usually happens if there is an impermeable layer of rock above the main water table, but it lies below the land surface. A perched water table often creates a spring at the point at which the flow of water intersects the surface. This is often seen in a valley wall, for instance.

Changing Water Tables

Water tables can change considerably for a few different reasons. For instance, on islands, the water table can be greatly affected by tides. As mentioned earlier, the seasons can also cause the water tables to change. Depending on the area, the water tables can be much lower in the summer.

Understanding how water tables behave in a certain region is imperative to making good land development choices.

If you are planning a land development project, a civil engineer can help you better understand this type of information and how it will affect your particular project.

Categorised in: Geotechnical Engineering