Beneath us, groundwater can be found in both soils, sediments, and solid rock. Soils and sediments are considered to be unconsolidated material, which is comprised of loose sediments and particles like sand and silts that are not cemented together by minerals. Rocks and bedrock are consolidated materials, which have grains of sediment cemented and bound together in a more compactmanner. Whether or not groundwater gets into unconsolidated and consolidated materials depends on some of the characteristics of those materials.
The flow of water downward from the land surface into and through the upper soils layers is called infiltration, or sometimes percolation. This water can be from precipitation, melting snow, human sources, and in some cases, small streams or ponds. Gravityand water properties are natural forces encouraging infiltration. There in an attraction between soil particles and water that exerts a tension and attraction that draws moisture readily downward into the soil.
Once water infiltrates into the soil, it will move downward through an unsaturated zone or vadose zone. In this layer of soil, some of the spaces between soil particles are filled withwater, and some are filled with air. While the pull of gravity tends to draw water downward, some water does remain between soil particles because of some properties of water cohesion and adhesion. There is an attraction of water molecules to one another and an attraction of water molecules to soil particles. Often there in a film of water that exists around soil particles called hygroscopic water,which can be absorbed by plant roots.
If gravity exerts a force sufficient enough to overcome cohesion and adhesion, the excess water (that is not hygroscopic water) will flow further downward. This water is called gravitational water or free water and the process is called gravity drainage.
Gravitational water that travels downward will eventually reach a soil/rock layer that is completely fullof water. This is the saturated zone. In this zone, all the pore spaces and voids in the soil and rock are filled with water. The upper boundary of the saturated zone is called groundwater table or simply water table. If a hole was drilled below the water table into the saturated zone, water from the surrounding saturated zone would flow into the hole and fill it to the level of the water table.The saturated zones and beds of material underground that can carry and store water are called aquifers. Aquifers can act as storage units able to supply sufficient quantities of water for municipal or household wells. Aquifers can have many different names and characteristics, usually relating to the types of soil and rock that compose them.
As expected, water in saturated zones and aquifersdoes not stay still. It can move further downward or it can flow horizontally though the satured zone. There are many factors that influence this water movement underground and the quantity of water stored in these various zones. Some of these factors that influence groundwater movement are discussed below.
The main factor in the amount of space available between particles, sediments, and rocks inthe soil layers and spaces between particles in rocks and rock layers. The amount of pore space in soil, sediments, and rock is called porosity, which can also be defined as the percentage of a material’s total volume that is taken up by pores. This “empty” space has a fantastic ability to hold water that seeps down from the land surface. Material with good porosity can be called “porous”.Mathematically, porosity can be expressed as the ratio of the volume of pore space to the total volume of the material as given by the following formula:
Dissolve them causing openings within the rocks to widen, possibly wide enough to become caves.
Keep in mind, sediments that have high porosity and permeability tend to form rocks with the same characteristics; for instance, sands form sandstones...