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rSPRING DEVELOPMENTS

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Springs, in geology, natural flow of water from the ground or from rocks, representing an outlet for the water that has accumulated in permeable rock strata underground. Some of the water that falls as rain soaks into the soil and is drawn downward by gravity to a depth where all openings and pore spaces in the rock or soil have become completely saturated with water. This region is called the zone of saturation, and the water it holds, groundwater. The upper surface of the zone of saturation is called the water table. Above the water table lies the zone of aeration, where the pore spaces in the soil are quite dry and are filled with air. When the upper surface of the groundwater (water table) intersects a sloping land surface, a spring appears. The occurrence of springs is closely related to the geology of an area. If an impervious layer of rock, such as a clay deposit, underlies a layer of saturated soil or rock, then a line of springs will tend to appear on a slope where the clay layer outcrops. Igneous rocks are also impervious to water, yet they are often extensively fractured, and springs commonly appear where these fractures come to the surface. Fractures in limestone are often enlarged by the dissolving action of groundwater, forming small underground channels and caves.

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Where these channels outcrop, springs are likely to be found. Springs are common along major faults because groundwater reaches the surface along the fault plane. Lines of springs help locate the position of faults such as the San Andreas of California. Springs can be a valuable water resource, and improvement in flow can often be accomplished simply by driving a pipe into the ground at the point where water seeps from the ground. Sometimes it is advisable to divert the spring water into a cistern or other storage reservoir from which the water can be pumped at will. When the water, because of the geological structure of the strata, issues under pressure, the spring is called artesian (see artesian well). Another type of spring is the geyser. Hot springs occur when the water issues from great depths or is heated by near-surface hot volcanic rock, as in Yellowstone National Park, Iceland, and New Zealand. Mineral springs are those with a high mineral content, usually silica or lime, dissolved from the rocks through which the water has passed (see mineral water). Many ancient city-states, such as Troy, had their sites determined by springs. Pioneer farmhouses often were located in the same way

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rGravity springs, which include

*depression springs;

*contact springs; and

*fracture or tubular springs.

Artesian springs, which include

*Artesian fissure springs; and

*Artesian flow springs.

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rDepression springs are formed when the land surface dips (forms a depression) and makes contact with the water table in permeable material. Water yield will be good if the water table is high, but the amount of available water may fluctuate seasonally. A gravity depression spring may not be suitable for a drinking water source since it may dry up.

Contact springs are formed when downward movement of underground water is restricted by an impervious underground layer and the water is pushed to the surface. This type of spring usually has a very good flow throughout the year and is a good water source

Fracture and tubular springs are formed when water comes from the ground through fractures or joints in rocks. Often the discharge is at a single point and protection is relatively easy. Fracture and tubular springs also offer a good source of water for a community supply.

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Holes up or Holes down?Half-perforated pipes are laid 'holes up' or 'holes down' depending on their intended use - see diagram. In most applications, the pipes are laid with the holes to the bottom of the pipe; the hydrostatic gradient discussed above ensures that the pipe functions as a conduit for groundwater. For collector drains, however, or for systems that are connected to conventional drainage systems, the pipes should be laid with the holes uppermost.

Collector DrainHoles at top

Dispersal DrainHoles at bottom