Hydraulic head measures energy in groundwater, shown in feet or meters of water height. Piezometers measure hydraulic head in aquifers for pumping or tracking water flow. Unconfined water tables connect to surface water, while confined aquifers are not directly connected. Wells require knowledge of hydraulic head and flow rates, and groundwater can vary due to human effects.
Hydraulic head is a measure of the amount of energy available in groundwater due to pressures in a water table or the height of the water level in the ground. Often called a head, the measurement is shown in feet or meters of water height, usually referred to as sea level to provide a standard measurement. A piezometer, which is a small diameter pipe open only at the top and bottom, can be used to measure the height of the water resulting from the hydraulic head in an aquifer. These measurements can be used to determine the water available for pumping operations or to measure and track water flow in underground supplies.
There are two types of underground water supply. An unconfined water table connects to a lake, stream, or other ground-level water source. Water can move freely between the lake and the underground aquifer based on rainfall or water use. Confined aquifers are layers of aquiferous sands or rocks contained between layers of solid rock and are not directly connected to surface waters. Wells are often drilled into confined aquifers because they may not be easily disrupted by drought or surface water loss and can provide more consistent water supplies.
Providing a well water supply requires knowledge of underground aquifers, available hydraulic head and available flow rates. Companies will first place piezometers in selected locations that confirm water availability and allow for hydraulic head measurements. Once the piezometric survey is complete, well locations can be chosen and drilled to the depth needed to provide the best hydraulic head. Groundwater pressure can be important, because low pressure requires larger pumps to provide adequate lifting force to get water. A final test is to run the well at full flow for a specified amount of time, which confirms that the aquifer accessed by the well can provide adequate water.
Groundwater or aquifers can vary greatly from season to season, due in part to different amounts of precipitation. A major effect on groundwater supplies are human effects, mostly caused by agriculture or ranching. In some parts of the world, growing crops requires large amounts of water, and surface water resources are often unavailable or unreliable for consistent crop quality. Wells provide a more substantial supply, but large water demands can deplete or deplete groundwater aquifers that cannot be recharged quickly.
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