Groundwater Chapter 6.3

What is Groundwater? It is hard to imagine groundwater because it is underneath our feet, but we can’t see it. Believe it or not, there is more water underneath the ground, then there is in lakes, rivers and streams. In fact, if you drank some water today or took a shower, it was most likely from groundwater. The ocean is has an abundance of water but it is mostly unusable to us as humans because it is saltwater. Groundwater moves underground through aquifers, which are permeable rock layers or sediments that allow water to flow through them freely.

Aquifers

Understanding Aquifers Underneath the ground there are two zones. The zone found under ground that does not contain groundwater is called the zone of aeration. The zone found under ground that does contain groundwater is called the zone of saturation. The line that separates these two zones is called the water table. The amount of water that can be stored in the zone of saturation depends on how much empty pore spaces there are, which is called its porosity. The porosity of an aquifer can determine how fast water can flow through it. The speed at which water can move through an aquifer is called its permeability.

Understanding Aquifers

What are Springs When the water table intersects the ground surface, a spring forms. When springs are close to magma underground, a hot spring can be formed. When a hot spring shoots up out of the ground at regular intervals and then the water drains back into the aquifer again, this can form a geyser. A well is simply a man-made hole drilled into the ground to reach the water table. An artesian well is a natural well that forms when the water table rises up against the force of gravity.

Springs and Wells

Geysers and Hot Springs

How does an artesian well form? In order to have an artesian well you have to have some unique conditions. You must have an aquifer that is contained by aquicludes (also sometimes called an aquitards). An aquiclude or an aquitard is an impermeable layer of rock or soil. You must also have an aquifer that is on a slope so that the recharge area (source of water) is higher than the discharge area (the sight of the artesian well). It is similar to using a siphon hose.

Artesian Wells

Caves and Karst Topography When rainwater that is acidic permeates into the ground and reaches areas with limestone bedrock, the acid dissolves the calcite (limestone) minerals. The empty spaces left behind when the limestone dissolves forms caves (or caverns). The water that drips into the caves leaves behind small amounts of calcite behind. This forms stalactites on the ceiling and stalagmites on the cavern floor. The ground located above caverns can form uneven ground with lots of depressions called sinkholes. This type of terrain is called Karst Topography.

Caves and Karst Topography