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In subsurface hydrogeology, drawdown is the reduction in hydraulic head observed at a well in an aquifer, typically due to pumping a well as part of an aquifer test or well test. In surface water hydrology and civil engineering, drawdown refers to the lowering of the surface elevation of a body of water, the water table, the piezometric surface ...
Cross section showing the water table varying with surface topography as well as a perched water table Cross-section of a hillslope depicting the vadose zone, capillary fringe, water table, and the phreatic or saturated zone. (Source: United States Geological Survey.) The water table is the upper surface of the zone of saturation.
Measuring hydraulic head in an artesian aquifer, where the water level is above the ground surface. Hydraulic head or piezometric head is a specific measurement of liquid pressure above a vertical datum. [1] [2] It is usually measured as a liquid surface elevation, expressed in units of length, at the entrance (or bottom) of a piezometer.
In the case of fresh water where the contents are under atmospheric pressure, 1psi = 27.7 inH 2 O / 1Pa = 9.81 mmH 2 O. The basic equation for such a measurement is = where P = pressure, ρ = density of the fluid, g = standard gravity, h = height of fluid column above pressure sensor Leak testing
However, when the local water table height is within said five meters, the total stress felt five meters below the surface is decreased by the product of the height of the water table in to the five meter area, and the specific weight of water, 9.81 kN/m^3. This parameter is called the effective stress of the soil, basically equal to the ...
Specific yield (S y) is also a ratio between 0 and 1 (S y ≤ porosity) and indicates the amount of water released due to drainage from lowering the water table in an unconfined aquifer. The value for specific yield is less than the value for porosity because some water will remain in the medium even after drainage due to intermolecular forces.
In hydrogeology, an aquifer test (or a pumping test) is conducted to evaluate an aquifer by "stimulating" the aquifer through constant pumping, and observing the aquifer's "response" in observation wells. Aquifer testing is a common tool that hydrogeologists use to characterize a system of aquifers, aquitards and flow system boundaries.
The cone penetration or cone penetrometer test (CPT) is a method used to determine the geotechnical engineering properties of soils and delineating soil stratigraphy. It was initially developed in the 1950s at the Dutch Laboratory for Soil Mechanics in Delft to investigate soft soils.