Irrigation, Drainage & Pumping Systems

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).

Step-by-step hydraulic calculation:
Discharge $Q = 450\text{ L/min} = \frac{450}{60} = 7.5\text{ L/s}$
Total head $H = 50\text{ m}$
Pump efficiency $\eta_p = 65\% = 0.65$
Metric Water Horse Power (WHP):

$$\text{WHP} = \frac{Q (\text{L/s}) \times H (\text{m})}{75} = \frac{7.5 \times 50}{75} = 5.0\text{ hp}$$

Shaft Horse Power (SHP) required:

$$\text{SHP} = \frac{\text{WHP}}{\eta_p} = \frac{5.0}{0.65} = 7.692\text{ hp}$$

Selecting standard commercial electric motor sizing among the given options gives 7.50 hp (Option 2).

Irrigation terminology:
Delta (

\(\Delta\))\lt /strong\gt : The total depth of irrigation water required by a crop during its entire base period in the field. Because it represents a linear depth/thickness of water layer, it is measured and expressed in units of length: \lt strong\gt centimeters (cm)\lt /strong\gt or meters (m). \[\Delta = \frac{864 \cdot B}{D}\]

where \(B\) is base period (days) and \(D\) is duty (hectares/cumec).
cm/hr is a unit of rainfall intensity or infiltration rate.
Poise is a unit of dynamic viscosity.
Lux is a unit of illuminance.

Therefore, Delta is expressed in (A) only.