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Groundwater Storage Presentation
Transcript of Groundwater Storage Presentation
Justin Case Terry Finkbiner In groundwater storage. The water is still moving, possibly very slowly, and it is still part of the water cycle. Most of the water in the ground comes from precipitation that infiltrates downward from the land surface. The upper layer of the soil is the unsaturated zone, where water is present in varying amounts that change over time, but does not saturate the soil. Groundwater occurs only close to the Earth's surface. There must be space between the rock particles for ground water to occur, and the Earth's material becomes denser with more depth. Essentially, the weight of the rocks above condense the rocks below and squeeze out the open pore spaces deeper in the Earth. That is why ground water can only be found within a few miles of the Earth's surface. About 1.7 percent of all of Earth's water is ground water and about 30.1 percent of freshwater on Earth occurs as ground water. As the bar chart shows, about 5,614,000 cubic miles (mi3), or 23,400,000 cubic kilometers (km3), of ground water exist on Earth. About 54 percent is saline, with the remaining 2,526,000 mi3 (10,530,000 km3) , about 46 percent, being freshwater. The pumping of wells can have a great deal of influence on water levels below ground, especially in the vicinity of the well, as this diagram shows. If water is withdrawn from the ground at a faster rate that it is replenished by precipitation infiltration and seepage from streams, then the water table can become lower, resulting in a "cone of depression" around the well. Depending on geologic and hydrologic conditions of the aquifer, the impact on the level of the water table can be short-lived or last for decades, and the water level can fall a small amount or many hundreds of feet. Excessive pumping can lower the water table so much that the wells no longer supply water—they can "go dry." The top of the surface where ground water occurs is called the water table. In the diagram, you can see how the ground below the water table is saturated with water (the saturated zone). Aquifers are replenished by the seepage of precipitation that falls on the land, but there are many geologic, meteorologic, topographic, and human factors that determine the extent and rate to which aquifers are refilled with water. Rocks have different porosity and permeability characteristics, which means that water does not move around the same way in all rocks. Thus, the characteristics of groundwater recharge vary all over the world.