Water Drawdown

Water Drawdown


the temporary lowering of the level or pressure of ground water when constructing foundation pits, mining mineral deposits, driving tunnels, or constructing subways. Water drawdown is achieved by various means depending on the depths of the workings being drained and on the permeability properties of the rock. Drawdown utilizing drill holes equipped with sucker-rod or centrifugal borehole pumps makes it possible to lower the water level to as deep as 300 m. Light well points permit drawdown to depths of 4-5 m when the length of the working member of the well points is up to 8 m. For drawdown to more than 5 m, well points are installed in several tiers. The best results using light well points are obtained in water-bearing sands of uniform composition and with seepage coefficients of 1-5 m per day. Drawdown by means of ejector pumps is possible up to a depth of 22 m. The pump consists of ejector well points, centrifugal pumps, and distributing and collector pipelines. Each well point has a water-jet lifter or ejector at the bottom of the installation. The ejector well points are recommended for use in water-bearing sands of uniform composition and structure that have a seepage coefficient of up to 0.1 m per day. A vacuum-concentric well drawdown device was developed in the USSR in 1967 for the complex conditions of draining alternating seams of water-bearing and water-resistant rock. The vacuum-concentric well device consists of an ejection well point with a filter jacket running the entire height of the water-bearing horizon. All water-bearing strata revealed by the well are drained by this device, and vacuuming is done by means of the ejector, which speeds the draining process. Open-drainage pumping equipment is used to pump ground water that flows into foundation pits at construction projects.

In cases where mining operations cut across an entire water-bearing stratum it is necessary to supplement draw-down with drainage.


Vodoponiihenie v stroitel’stve. Moscow, 1971.


References in periodicals archive ?
According to studies when the reservoir water drawdown rate increases, drains impact on upstream crust pore water pressure reduction and finally, dam stability will increase.
Limit analysis of submerged slopes subjected to water drawdown.
The fact that root systems are branched and that the water drawdown of individual roots overlap in geometrically complicated patterns necessitates the extension of the Gardner model to the whole root model.
Root D is actually 2 roots touching each other and will be regarded here as 1 root with regard to water drawdown.
Water extraction between 15-mm-spaced roots Water drawdown in the inter-root area usually shows a convex shape from the root surface to the region of moist soil (Fig.
An interesting observation is the shape and magnitude of the water drawdown curve of inter-root areas that occurs in almost all pots (Fig.
The lake bed has been exposed by an eight-foot water drawdown.
There are many pieces to the Salmon Puzzle, dams, habitat, stream conditions, water drawdown, over fishing, El-Nino, pollution, interceptions and politics.
In contrast, water drawdown by plant roots grown at low soil water potential (<-30 kPa) has received much less attention from researchers.
Newman's conclusion has been supported by CAT studies on water drawdown by lupin and radish plants at high water potentials (Hamza and Aylmore 1992a).
Understanding the nature and extent of the overlapping between the drawdown areas and the beam hardening-altered bulk density area is thus important in studying water drawdown by plant roots growing at low soil water content.
Elucidation of these uncertainties requires the ability to study soil water drawdowns around plant roots quantitatively in situ in a non-destructive, non-invasive, and continuous fashion using a high resolution technique, such as computer-assisted tomography, applied to the attenuation of X- and gamma-radiation (CAT scanning) (Aylmore 1993).