| A | B |
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| unconfined aquifers | In unconfined aquifers, water has simply infiltrated from the surface and saturated the subsurface material. If people drill a well into an unconfined aquifer, they have to install a pump to push water to the surface. |
| confined aquifers | Confined aquifers have layers of rock above and below it that are not very permeable to water. Natural pressure in the aquifer can exist; pressure which can sometimes be enough to push water in a well above the land surface. No, not all confined aquifers produce artesian water, but, as this picture of an artesian well in Georgia, USA shows, artesian pressure can force water to the surface with great pressure. |
| 1.7% | percent of earth's water that is groundwater |
| 30% | percent of earth's freshwater that is groundwater |
| posority | a measure of the water-bearing capacity of subsurface rock. With respect to water movement, it is not just the total magnitude of porosity that is important, but the size of the voids and the extent to which they are interconnected, as the pores in a formation may be open, or interconnected, or closed and isolated. For example, clay may have a very high porosity with respect to potential water content, but it constitutes a poor medium as an aquifer because the pores are usually so small. |
| percolation | The movement of water through the openings in rock or soil. (2) the entrance of a portion of the streamflow into the channel materials to contribute to ground water replenishment. |
| permeability | the ability of a material to allow the passage of a liquid, such as water through rocks. Permeable materials, such as gravel and sand, allow water to move quickly through them, whereas unpermeable material, such as clay, don't allow water to flow freely. |
| aquaculture | farming of plants and animals that live in water, such as fish, shellfish, and algae. |
| aquifer | a geologic formation(s) that is water bearing. A geological formation or structure that stores and/or transmits water, such as to wells and springs. Use of the term is usually restricted to those water-bearing formations capable of yielding water in sufficient quantity to constitute a usable supply for people's uses. |
| artesian water | ground water that is under pressure when tapped by a well and is able to rise above the level at which it is first encountered. It may or may not flow out at ground level. The pressure in such an aquifer commonly is called artesian pressure, and the formation containing artesian water is an artesian aquifer or confined aquifer. |
| capillary action | the means by which liquid moves through the porous spaces in a solid, such as soil, plant roots, and the capillary blood vessels in our bodies due to the forces of adhesion, cohesion, and surface tension. Capillary action is essential in carrying substances and nutrients from one place to another in plants and animals. |
| consumptive use | -that part of water withdrawn that is evaporated, transpired by plants, incorporated into products or crops, consumed by humans or livestock, or otherwise removed from the immediate water environment. Also referred to as water consumed. |
| conveyance loss | water that is lost in transit from a pipe, canal, or ditch by leakage or evaporation. Generally, the water is not available for further use; however, leakage from an irrigation ditch, for example, may percolate to a ground-water source and be available for further use. |
| desalination | the removal of salts from saline water to provide freshwater. This method is becoming a more popular way of providing freshwater to populations. |
| discharge | the volume of water that passes a given location within a given period of time. Usually expressed in cubic feet per second. |
| drainage basin | land area where precipitation runs off into streams, rivers, lakes, and reservoirs. It is a land feature that can be identified by tracing a line along the highest elevations between two areas on a map, often a ridge. Large drainage basins, like the area that drains into the Mississippi River contain thousands of smaller drainage basins. Also called a "watershed." |
| drip irrigation | a common irrigation method where pipes or tubes filled with water slowly drip onto crops. Drip irrigation is a low-pressure method of irrigation and less water is lost to evaporation than high-pressure spray irrigation. |
| domestic water use | water used for household purposes, such as drinking, food preparation, bathing, washing clothes, dishes, and dogs, flushing toilets, and watering lawns and gardens. About 85% of domestic water is delivered to homes by a public-supply facility, such as a county water department. About 15% of the Nation's population supply their own water, mainly from wells. |
| drawdown | a lowering of the ground-water surface caused by pumping |
| erosion | the process in which a material is worn away by a stream of liquid (water) or air, often due to the presence of abrasive particles in the stream. |
| estuary | a place where fresh and salt water mix, such as a bay, salt marsh, or where a river enters an ocean. |
| evaporation | the process of liquid water becoming water vapor, including vaporization from water surfaces, land surfaces, and snow fields, but not from leaf surfaces |
| evapotranspiration | the sum of evaporation and transpiration. |
| flood | An overflow of water onto lands that are used or usable by man and not normally covered by water. Floods have two essential characteristics: The inundation of land is temporary; and the land is adjacent to and inundated by overflow from a river, stream, lake, or ocean. |
| flood, 100 year | A 100-year flood does not refer to a flood that occurs once every 100 years, but to a flood level with a 1 percent chance of being equaled or exceeded in any given year. |
| flood plain | a strip of relatively flat and normally dry land alongside a stream, river, or lake that is covered by water during a flood. |
| flood stage | The elevation at which overflow of the natural banks of a stream or body of water begins in the reach or area in which the elevation is measured. |
| flowing well/spring | a well or spring that taps ground water under pressure so that water rises without pumping. If the water rises above the surface, it is known as a flowing well. |
| gage height | the height of the water surface above the gage datum (zero point). |
| gaging station | a site on a stream, lake, reservoir or other body of water where observations and hydrologic data are obtained. |
| geyser | a geothermal feature of the Earth where there is an opening in the surface that contains superheated water that periodically erupts in a shower of water and steam. |
| glacier | a huge mass of ice, formed on land by the compaction and recrystallization of snow, that moves very slowly downslope or outward due to its own weight. |
| greywater | wastewater from clothes washing machines, showers, bathtubs, hand washing, lavatories and sinks. |
| groundwater | (1) water that flows or seeps downward and saturates soil or rock, supplying springs and wells. The upper surface of the saturate zone is called the water table. (2) Water stored underground in rock crevices and in the pores of geologic materials that make up the Earth's crust. |
| headwater(s) | (1) the source and upper reaches of a stream; also the upper reaches of a reservoir. (2) the water upstream from a structure or point on a stream. (3) the small streams that come together to form a river. Also may be thought of as any and all parts of a river basin except the mainstream river and main tributaries. |
| hydrologic cycle | the cyclic transfer of water vapor from the Earth's surface via evapotranspiration into the atmosphere, from the atmosphere via precipitation back to earth, and through runoff into streams, rivers, and lakes, and ultimately into the oceans. |
| impermeable layer | a layer of solid material, such as rock or clay, which does not allow water to pass through. |
| infiltration | flow of water from the land surface into the subsurface. |
| leaching | the process by which soluble materials in the soil, such as salts, nutrients, pesticide chemicals or contaminants, are washed into a lower layer of soil or are dissolved and carried away by water. |
| levee | a natural or manmade earthen barrier along the edge of a stream, lake, or river. |
| clay | 0.00024-0.004 millimeters (mm); the diameter, in millimeters, of suspended sediment or bed material. |
| silt | 0.004-0.062 mm;the diameter, in millimeters, of suspended sediment or bed material. |
| sand | 0.062-2.0 mm; and the diameter, in millimeters, of suspended sediment or bed material. |
| peak flow | the maximum instantaneous discharge of a stream or river at a given location. |
| per capita use | the average amount of water used per person during a standard time period, generally per day. |
| percolation | (1) The movement of water through the openings in rock or soil. (2) the entrance of a portion of the streamflow into the channel materials to contribute to ground water replenishment. |
| permeability | the ability of a material to allow the passage of a liquid, such as water through rocks. Permeable materials, such as gravel and sand, allow water to move quickly through them, whereas unpermeable material, such as clay, don't allow water to flow freely. |
| porosity | a measure of the water-bearing capacity of subsurface rock. |
| potable water | water of a quality suitable for drinking. |
| precipitation | rain, snow, hail, sleet, dew, and frost. |
| recharge | water added to an aquifer. For instance, rainfall that seeps into the ground. |
| reservoir | a pond, lake, or basin, either natural or artificial, for the storage, regulation, and control of water. |
| runoff | (1) That part of the precipitation, snow melt, or irrigation water that appears in uncontrolled surface streams, rivers, drains or sewers. Runoff may be classified according to speed of appearance after rainfall or melting snow as direct runoff or base runoff, and according to source as surface runoff, storm interflow, or ground-water runoff. (2) The total discharge described in (1), above, during a specified period of time. (3) Also defined as the depth to which a drainage area would be covered if all of the runoff for a given period of time were uniformly distributed over it. |
| sediment | usually applied to material in suspension in water or recently deposited from suspension. |
| sedimentary rock | rock formed of sediment, and specifically: (1) sandstone and shale, formed of fragments of other rock transported from their sources and deposited in water; and (2) rocks formed by or from secretions of organisms, such as most limestone. |
| storm sewer | a sewer that carries only surface runoff, street wash, and snow melt from the land. |
| stream | a general term for a body of flowing water; natural water course containing water at least part of the year. In hydrology, it is generally applied to the water flowing in a natural channel as distinct from a canal. |
| stream flow | the water discharge that occurs in a natural channel. |
| subsidence | a dropping of the land surface as a result of ground water being pumped. Cracks and fissures can appear in the land. |
| surface water | water that is on the Earth's surface, such as in a stream, river, lake, or reservoir. |
| tributary | a smaller river or stream that flows into a larger river or stream. Usually, a number of smaller tributaries merge to form a river. |
| unsaturated zone | the zone immediately below the land surface where the pores contain both water and air, but are not totally saturated with water. |
| watershed | the land area that drains water to a particular stream, river, or lake. |
| xeriscaping | a method of landscaping that uses plants that are well adapted to the local area and are drought-resistant. |
