Piezometer

Piezometer is a device used for the measurement of hydraulic head in aquifers. The most simple piezometer is a small diameter well in communication with the water through a filter zone on the perimeter. If the filter zone is located at a specific isolated depth, the piezometer is defined punctual, or, if the piezometer has a filter on all its length, is defined windowed. The windowed piezometer is cheaper than the punctual one, but cannot give information on vertical flows. The main problem with the piezometers is the time-lag between the variation of piezometric level in the acquifer and the respective variation in the piezometer. This time-lag is related to the piezometer (type, shape, ecc.) and the soil. Modern piezometers with little time-lag are the piezometric cells, where the pression on a membrane is measured by the pression of gas (peneumatic piezometric cells), by a vibrating thread estensimeters or by electrical estensimeters (strain gauges piezometers).