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The Water Table

By Justin Sexton

Most people know that the "water table" has something to do with groundwater. There is also a general understanding that in times of serious drought, water table levels may drop and wells may run dry.  Water flows downward through soil and bedrock because of the force of gravity. It continues in that direction until a depth of about 3 miles is reached, where porosity and permeability cease. (Porosity is a measure of how much of a rock is open space. This space can be between grains or within cracks or cavities of the rock. Permeability is a measure of the ease with which water can move through a porous rock. The pore space above this level begins to fill progressively upward with groundwater.)

 

A Place Between The Saturation Zone & The Unsaturated Zone

The rock and soil in which all the open spaces are filled with water is called the saturation zone. As the top of the saturated zone rises toward the surface, it reaches a level of equilibrium with the overlying unsaturated zone. The unsaturated zone (or zone of aeration) is the rock and sediment in which pore spaces contain mostly air and some water and therefore are not saturated. The unsaturated zone typically starts at the surface and extends downward to the saturated zone. The contact between the saturated and unsaturated zones is called the water table.

The depth of the water table can change (rise or fall) depending on the time of year. During the late winter and spring, when accumulated snow starts to melt and spring rainfall is plentiful, water on the surface infiltrates into the ground, and the water table rises. When the plants start to grow again in the spring, and precipitation gives way to hot/dry summers, the water table falls because of evapotranspiration (the process by which water is transferred from the land to the atmosphere by evaporation from the soil and other surfaces and by transpiration from plants).

 

How Does The Water Table Affect My Home?

The groundwater table plays a role in home construction, foundation stability, and home comfort. The water table, as well as local soil conditions, and drainage can impact homes and their foundations. If soil drains efficiently and there is a relatively low water table, it may not be problematic. However, if soil is dense and absorbent and the water table is high, the ground around a home may swell and become saturated. This can exert significant pressure against the foundation walls. (CLICK HERE to learn more from Brian about how groundwater affects a home's foundation)

Even if ground water does not cause foundation cracking or shifting, it could lead to humidity issues. This can cause rust, bacteria, and mold in your home. Wood structures in a home may be compromised by a high level of humidity.

Did you know… Groundwater, which is in aquifers (a body of permeable rock which can contain or transmit groundwater) below the surface of the Earth, is one of the Nation's most important natural resources. Groundwater is the source of about 37% of the water that county and city water departments supply to households and businesses (public supply). It provides drinking water for more than 90% of the rural population.

Tags: Causes

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