In tubewell construction, a gravel pack (gravel envelope) is placed in the annular space between the borehole and the slotted well screen to prevent sand ingress and stabilize fine aquifer material. The standard recommended thickness of the gravel envelope ranges between 8 to 15 cm (approx. 3 to 6 inches). A thickness less than 7.5-8 cm may leave voids, while a thickness exceeding 15-20 cm makes well development difficult.

Vertical drainage: Relies on deep tubewells or pumping wells to extract excess groundwater from deep semi-confined or unconfined aquifers and lower waterlogged water tables -> (IV).
Stuffing box: A mechanical component on the shaft of a centrifugal pump containing packing rings to prevent liquid leakage from pump casing -> (III).
Diffuser: A stationary casing ring with expanding guide vanes fitted in deep-well turbine pumps to efficiently convert the kinetic energy of water leaving the impeller into pressure head -> (II).
Groundwater recharge: The natural or artificial replenishment of groundwater through deep percolation of surface water -> (I).

Rainguns (giant sprinkler guns) operate at high pressures ranging from 3.0 to 9.0 $\text{kg/cm}^2$ (approx. 300 to 900 kPa or 30 to 90 m pressure head). At this operating pressure, they deliver high discharge rates of 200 to 1,200 L/min and cover a wetting diameter of 50 to 120 meters.